by
B.M. Pawson & R.E. Gold

ABSTRACT

Two baits, hydramethylnon (American Cyanamid Company) and hexaflumuron (DowElanco – Sentricon Colony Elimination System), were evaluated for the control of subterranean termites in Texas. Hydramethylnon bait was tested for one year at four structures infested with subterranean termites. Control of termites was not achieved; however, colony suppression, as indicated by the number of wood stakes attacked by termites, may have occurred at two locations. Hexaflumuron bait was tested for two years at seven structures infested with subterranean termites. Control of termites occurred at one location where more than 17 Baitubes were consumed. Colony suppression, as indicated by the number of monitoring stations attacked by termites, appears to have occurred at two structures. With both hydramethylnon and hexaflumuron, lack of termite activity at bait stations might indicate a reduction in colony population size (or elimination); however, independent monitoring stations (wooden stakes and wood blocks) used during these tests indicated that termites were present even though termites were not detected in the bait stations.

INTRODUCTION

  Interest and support in the development and evaluation of baits for termite control has increased markedly in the past ten years. The concept of using baits for subterranean termite control program dates back to 1968 (Esenther & Grey 1968). Beard (1974) advocated the use of baits and recognized the need for a slow acting active ingredient  (A.I.). Li et al. (1976) evaluated mirex (dechlorane) for the control of the Australian subterranean termite (Macrotermes darwiniensis Froggatt). The concept of utilizing a bait rather than the more traditional chemical barrier methods has great appeal to those that are concerned about the potential problems associated with the use of large quantities of termiticide in and around structures where people live and work. Through the use of baiting systems, it may be possible to either reduce or eliminate termite populations (colonies) with the use of very small amounts of pesticide (g instead of Kg). This concept is based on termites accepting the bait matrix. There has been some controversy over the terminology associated with bait acceptability (Grace 1991, Grace et al. 1989). Some commercial manufacturers of potential baits are interested in the development and marketing of baits which are attractive to foraging termites or that arrest them to the point where they will feed on the bait matrix. Other manufacturers are merely interested in the development of baits which are not repellent to foraging termites and that are tolerated or preferred over existing sources of cellulose.

One of the key elements in the development of a bait appears to be creating a matrix to which an insect growth regulator (IGR), or a slow acting toxicant can be added. A number of matrices have been reported as being acceptable to termites including: rolls of toilet paper (Haverty et al. 1975), corrugated cardboard (LaFage et al. 1983), cork (French et al. 1986) and wooden blocks (French & Robinson 198 1, Su & Scheffrahn 1990). Most of the early work with monitoring termite populations has involved the use of simple wooden stakes or blocks of wood which have proved to be acceptable to foragers (Esenther & Gray 1968, Esenther & Beal 1974, 1978, Ostaff & Gray 1975, Jones 1988, Su 1991). Esenther et al. (196 1) utilized decayed wood baits to create a chemical gradient which they believed recruited termite foragers. A review of the literature associated with semiochemical. attractants for termites is provided by Grace (1991).

Considerable work with various insect growth regulators and slow acting toxicants used as baits have been researched by Su (1994), Su & Scheffrahn (1988, 1989, 1991, 1993), and Su et al. (1987, 1991b, 1994, 1995a, and 1995b). Based on these reports, it appears that there have been successes in controlling termite populations with baits, and the commercial interest in this approach has expanded to include at least two federally registered products.
The purpose of this study was to provide an independent evaluation of various baiting systems. which are used for termite control. We utilized products from DowElanco and American Cyanamide in replicated field trials.

MATERIALS AND METHODS

Two different baits were evaluated for termite control. American Cyanamid’s bait uses hydramethy1non which is a slow acting toxicant. Hydramethylnon was evaluated for two years. DowElanco’s bait uses hexaflumuron which is an insect growth regulator. Hexaflumuron was evaluated for two years. For consistency, baiting strategies and protocols for each bait will be discussed separately.

American Cyanamid Company – Hydramethy1non.
During 1994-1995, four structures with, active termite infestations were used to test the effects of hydramethylnon bait against native termite populations. Three structures had infestations of Reticulitermes sp. and one structure had infestations of both Reticulitermes sp. and Coptotermes formosanus Two types of monitoring devices were used in this study. The first monitoring device was a diagnostic bait cartridge that was provided by the American Cyanamid Company. The second monitoring device was a modified wooden stake. The wooden stake was a 5 x 5 x 15cm piece of pine that had a 1.9cm hole drilled length-wise through the stake. In addition, 3mm holes were drilled through the sides of the stake. After being installed in the ground, pieces of cardboard were placed in the hollow of the wooden stake. A rubber stopper was inserted into the hole of the stake to serve as a cover.

A series of locations for monitoring devices were selected around the perimeter of each structure. At each locations, both monitoring devices, a placebo bait cartridge and a wooden stake, were installed in the ground. Distance between bait cartridge and wooden stakes was about 10cm while the distance between stations was about five meters. Distance between the monitoring devices (bait cartridges and wooden stakes) and the structure was about 20cm. The number of stations around the 4 structures were 37, 46, 20 and 45, respectively. Upon initial installation, all bait cartridges and wooden stakes/ cardboard were moistened with 30 – 40ml of water.

All four structures were visited on a monthly basis. On each visit, each placebo bait cartridge was pulled from the ground and visually inspected for termite activity and the amount of bait consumed. All wooden stakes were checked for termite activity at the same time; however, wooden stakes were not pulled from the ground. Instead, the rubber stoppers were removed exposing the cardboard in the center hole. Soil crusts (similar to feeding tubes) under the rubber stoppers indicated the presence of termites. Soil “crusts” were broken to make positive sightings If termites were present at either the placebo bait cartridge or the wooden stake, the bait cartridge was removed and an active bait cartridge was placed at the station. Any placebo bait cartridge that was discolored or moldy was discarded and a new placebo bait cartridge was installed. All newly installed cartridges were moistened with 30 – 40ml of water after placement.

During each monthly visit, the presence or absence of termites was recorded at each monitoring station along with the amount of bait consumed. If termites were present, the following termite population scale was used: 0 – no termites, no feeding; 1- no termites, but feeding occurred; 2 – 1 to 10 termites; 3 – 11 to 100 termites; 4 – 101-1000 termites; 5 – >1000 termites.

During 1995-1996, structures 3 and 4 were used to evaluate the effects of keeping active hydramethylon in bait stations on termite populations. Newly-developed housing units were installed around the two structures. Bait cartridges were screwed into these housing units. The cartridge and housing unit were covered with a plastic lid that clipped into the bait cartridges. Covered placements of bait cartridges and wooden stakes around the structures were concentrated in areas of known termite activity. Other bait cartridges and wooden stakes were placed at 15m intervals around the rest of the structure and at other potential termite locations within the yard. Twenty-six bait cartridges (paired with wooden stakes) were placed at both structures 3 and 4.

During monthly visits, all bait cartridges and wooden stakes were inspected for termite activity. After the bait cartridges were inspected, they were discarded. New cartridges were installed at each inspection. If a wooden stake was attacked, it was removed and a new wooden stake put in its place. The number of termites infesting the wooden stake, and the proportion of feeding damage to the stake were recorded.

DowElanco – Sentricon Colony Elimination System (Hexaflumuron).
During 1994-1995, seven urban structures (six residential and one commercial site) were selected. All structures had active termite problems. Structures were monitored using the Sentricon monitoring system with stations spaced between 3 and 5m apart. Sentricon stations were installed around the structures on May 4th and June Ist 1994.

Sentricon stations around structures were monitored on a monthly basis. After a station was attacked by termites, bucket/block traps were installed near the infested station. The bottom portion of a 17.7 x 19cm dia. plastic bucket was cut and discarded. Into the top 6.5cm of the bucket, 6mm holes (36) were drilled evenly spaced around the sides. Wood blocks consisted of six 1.9, x 8.9 x 12.7cm pieces of aged pine assembled into a rectangle having two ends and four inner pieces. The four inner pieces were separated from one another by pieces of 3mm wood applicator sticks that were held in place by staples. The four inner pieces were held together by drilling five 6mm holes through each end piece and inserting wood screws. When completely assembled, the wood block measured 8.9 x ‘ 12.7 x 12.7cm. Up to three bucket/block traps were installed at each structure. After one month, the bucket/ block traps were inspected for termite activity. If termite activity was sufficiently high (if block was completely, “sealed”), one trap was selected for marking procedures. At the selected trap site, the block of wood was removed and another block of wood put in its place. The former block of wood was returned to the laboratory where it was disassembled to obtain the termites. Termites were separated into castes and counted. Pseudergates were counted by weighing three samples of 100 individuals and then taking the overall weight. After counts, ca. 2g of termites were placed on filter paper stained with Nile Blue A. Termites remained on the filter paper for three to four days at which time they were removed from the filter paper and returned to the field and released at the trap site.

After each structure had some of its termites “marked”, the Sentricon baiting system was initiated. On a monthly basis, the stations surrounding each structure were inspected. If termites attacked a station, the termites were collected from the wooden stakes and placed inside the top of a Baitube which was placed in the station. During monthly visits, the presence/absence of termites in Baitubes and the amount of bait consumed was recorded. If, after two to three months, no termite activity was observed in a station having a Baitube it was removed, and the wooden stakes were placed back in the station.

During 1995-1996, six of the seven structures continued to be monitored using Sentricon stations. Because one site was dropped (Structure 5), one additional structure (#8) was added to the study. Forty-nine Sentricon stations were placed around this structure. A more active approach was taken during 1995-1996, and involved placing more stations around each home whenever they were needed. When new stations were installed, the newest Sentricon design station were installed.

RESULTS AND DISCUSSION

American Cyanamide Company – Hydramethy1non:
1994-1995: Structure 1. Structure 1 is a home of slab construction. It is a town house and has soil boarding on three sides. Twenty bait cartridge/wood stake stations were installed around the home on June 14th 1994. Because termites had severely attacked the right side (back) of the home, repairs/alterations were made after the study was initiated. As a result of the repairs, eight stations were removed. A total of 12 stations were monitored throughout the year.

At each inspection throughout the year, termite activity was higher in the wood stakes (12 occurrences) than in the bait cartridges (2 occurrences) (Table 1). Termite population levels at the wood stakes ranged from 2 (1 to 10 termites) to 4 (101 to 1000 termites), but were usually below 100 termites (scale= 3). Termites were encountered only twice in bait cartridges, once in a placebo bait cartridge and once in an active bait cartridge. In both cases, termites numbered less than 100 individuals (scale = 3). Of the12 stations installed around Structure 1, eight (67%) were attacked by termites (Reticulitermes sp.). Termites were active during the summer and fall of 1994 and the early summer of 1995. During the first sampling period, two of the eight stations were attacked, a placebo bait cartridge at one station and a wood stake at another station. Another four stations were attacked during the second sampling period (August 30th). The seventh station was attacked during the September 22nd sampling period. The last station attacked occurred during the May 17th visit (Table 1).

Although eight stations were attacked, termites only fed on bait cartridges at seven stations, and termite activity was observed in only one. The other six stations were considered attacked because it appeared.- tunneling had occurred in the bait cartridges. The amount of placebo and active bait consumed during each sampling period throughout the year is listed in Table 2. The total estimated amount of placebo bait consumed was just over one bait tube (1.09 tubes). All placebo bait consumption occurred during the months of July and August. The total estimated amount of active bait consumed was just under one bait tube (0.96 tube). Active bait consumption occurred over a four month period from August to November.

Termites were not controlled at Structure 1. Even though termite activity decreased markedly in all stations from January through May, the presence of termites during the May 17th and June 21st visits indicated termite control was not achieved.

Structure 2. Structure 2 is a home of slab construction with ca. 238m2. Forty-five bait cartridge/wood stake stations were installed around the home on June 14th 1994. Termites were encountered in the front of the house after an addition was made to the home. Swarming occurred in the spring of 1994.

As with Structure 1 termite activity was higher in the wood stakes (8 occurrences) than in the bait cartridges (4 occurrences) (Table 1). Only five stations around this home were attacked by termites (Reticulitermes sp.) Termite activity  occurred from July 1994 through January 1995. One station had termite activity during the first month of installment, and both the bait cartridge and the wood stakes were attacked.

Table 1. Summary of 1994-1995 & 1995-1996 field results using Hydromethylnon bait around structures in Texas. The numbers represent bait cartridges and wood stakes with active termites.

During all inspections, termite population levels were between 11 and 100 individuals (scale 3) or 101 to 1000 individuals (scale = 4). Termites were never encountered in active bait cartridges; however, they were found in placebo bait cartridges four times. It was estimated that termites fed on the placebo and active bait cartridges 6 and 10 times, and consumed 1.70 and 1.26 cartridges of bait, respectively (Table 2). Feeding on active bait cartridges appeared to be constant through seven months.

Although no termite activity was recorded at any station after the March 1995 visit, control of termites was not achieved. Two-thirds of the active bait consumed was prior to the return of termites in January 1995.

Table 2. Summary of 1994-1995 & 1995-1996 field results using Hydramethylnon bait around structures in Texas. The numbers represent bait cartridges attacked and the mean percentage of bait consumed by termites at the indicated time.

When the termites returned, they were in higher numbers than before the active bait cartridges were installed (scale of 4 compared to a scale of 2). Only one-third of the estimated active bait consumed occurred after January 1995. Because no termites were observed in the active bait cartridges, the amount of active bait actually consumed by termites is only an estimation. It appeared that termites may have detected hydramethylon in the bait. Termites attacked the placebo bait cartridge, but disappear when an active bait cartridge was used. Then, when a new placebo bait cartridge is put in place of the active bait cartridge, the termites return. This behavior appears to indicate that the active bait with hydramethylnon is not a preferred/ compatible bait. Placebo bait cartridges were attacked so active bait cartridges were placed in the ground in August. After two months of little to no feeding, they were replaced with placebo bait cartridges (October). After another two months (January), these cartridges were again attacked by termites.

Structure 3. Structure 3 is a home of pier and beam construction with ca. 208 M2 . Thirty-seven bait cartridge/wood stake stations were installed around the home on June 14th, 1994. Termite swarming has occurred from the eaves in the front of the house and along the back left side of the house.

Monthly inspections indicated that termites were more frequently encountered at wood stakes (18 occurrences) than at bait cartridges (12 occurrences) (Table 1). Of the 37 stations placed around this structure, 13 stations were attacked by termites (Reticulitermes sp.). Termite activity was recorded from August through November, during February and again during April. Most termite activity was recorded in late summer/fall period. One station (a wood stake) was attacked during the first sampling period (August).

Termites were encountered in both the bait cartridges and wood stakes at the same sampling period five times throughout the year. Of the 13 stations attacked during the year, wood stakes were attacked 11 times. Initial termite population estimates ranged from a scale of 3 (11 to 100 termites) to 4 (101 to 1000 termites). During subsequent inspections of the I I wood stakes that were attacked, termites either left the wood stake and did not return (6 occurrences) or left and returned at a later date (5 occurrences). Termites were encountered in bait cartridges 12 times during the year at 9 stations. Termites were usually found in the placebo bait cartridges (10 occurrences) when compared with active bait cartridges (2 occurrences) Even though termites were encountered in bait cartridges 12 times, termite feeding was estimated to have occurred 34 times (Table 2). Of these 34 times, feeding occurred 16 times in placebo bait cartridges and 18 times in active bait cartridges. The total estimated amount of placebo and active bait consumed was 5.79 and 2.02 cartridges, respectively. The most bait consumed during a sampling period from placebo and active bait cartridges was 70% and 15%, respectively.

It appears that a partial reduction in termite population may have occurred due to the baiting procedure. The termite foraging area appears to have decreased and is now concentrated between stations 8 through 15. Complete control has not be achieved.

Structure 4. Structure 4 is a home of slab construction with ca. 370m1. The back right hand corner of the home was backfilled. Termites (Coptotermes formosanus) have been at the home for several years. Spot treatments have been made in the kitchen area and outside walls in the recent past. Swarming has occurred during the first week of June for the last two years. Swarmers were found in the front right hand corner of the home (from the eaves – outside) and in back right hand corner of the home (garden room inside). Forty-six bait cartridge/ wood stake stations were installed around the home on June 14th, 1994.

Even though the home was being treated for Coptotermes formosanus, Reticulitermes sp. was encountered along the right front area of the home. Reticulitermes sp. attacked 3 of the 46 stations during the year (Table 1). Interestingly, Reticulitermes sp. was encountered in the bait cartridges (3 occurrences) more than the wood stakes (1occurrence): However, Reticulitermes sp. occupied the wood stake at station #1 almost continuously from November 1994 through June 1995. As with the other homes, Reticulitermes sp. consumed more of the placebo bait than the active bait (Tables 2). The estimated amount of placebo and active bait consumed by termites was 0.56 and 0.20 cartridges, respectively (Table 2).

Coptotermes formosanus attacked 17 of the 46 stations placed around this home, and activity was recorded continuously throughout the year (Table 1). Termite activity levels were high during the late summer (August/September) then decreased in the winter months before becoming very high in the spring. Coptotermes formosanus were encountered in 18 bait cartridges and 80 wood stakes throughout the year.

The number of placebo and active bait cartridges attacked was different during the year. The number of placebo bait cartridges attacked during the year  was 12, while the number of active bait cartridges  attacked was 33. The  amount of placebo and active bait consumed was 3.71 and 3.78, respectively. The amount of active bait consumed was almost twice as much as the amount consumed at any of the other homes. The high number bait cartridges attacked (45) is an indication of the severity of the termite problem at this home.

The termites have not been controlled at Structure 4. The high number of bait cartridges and wood stakes attacked throughout the year indicates that the termites were foraging for food. The increase in the termite population during the spring of 1995 is an indication that the termites were preparing to swarm. It also indicated the active bait had no effect on the termite population.

1995-1996: Structure 3. Termites were present throughout the year, but at low levels (Table 2). Over the course of the year, eight bait cartridges had been attacked, but only 25% of one bait cartridge was estimated to have been consumed during the year. Of the 26 paired stations around Structure 3, only two stations had termite activity during the year. Termites were present at these stations at the end of the year (Table 1).

Termites at Structure 3 have not been controlled. There has been no change in the number of locations attacked or the numbers of termites encountered throughout the second year of the study. Even though a new bait formulation was placed in the ground, insufficient time was given to determine if the new formulation had an effect on the termite population.

Structure 4. Reticulitermes sp. was present on the wood stakes throughout the year. During the summer (July and August), Reticulitermes sp. occurred at the same location they occupied during the 1994-1995 year. Even though practically no bait was consumed (less than 0.05% of one cartridge), the termites disappeared. In December, Reticulitermes sp. was present at another station about 20m away from the former station. Two additional bait cartridges were placed around the wood stake in an attempt to make the bait cartridges more accessible; however, even though more cartridges were in place, termites have not fed on any of the bait cartridges.

Coptotennes formosanus was active at both the bait cartridges and wood stakes throughout the year (Tables 1 & 2). An average of five bait cartridges were attacked by C. formosanus during each visit throughout the year. Even though many bait cartridges were attacked by C. formosanus, less than one half of one bait cartridges was consumed. An average of nine wood stakes were attacked by  C. formosanus during each visits throughout the year. Damage to the wooden stakes by C.formosanus ranged from 5 to 85%.

Reticulitermes sp. and C. formosanus were not controlled at this structure. Termites have remained very active throughout the year. Because termites did not fed to any great extent on the bait cartridges, and they fed continuously on the wood stakes, wood stakes were modified in an attempt to deliver more bait material to the termites. Modifications to the wood stake included securing a piece of plastic around the bottom of the wood stake. Then, bait was poured into the center of the wood stake surrounding one piece of cardboard. Again, a rubber stopper served as its cover. Modified wooden stakes were placed in the ground on April 23rd and only in locations previously attacked by C. formosanus. The two following sampling periods showed that termites were no longer actively feeding on the wooden stakes. Damage to the wooden stakes was superficial, just surface etching (1 to 2% damage) and little to no bait was consumed. Before the wooden stakes were modified, damage ratings approached 70 to 80% during a sampling period.

DowElanco-Sentricon Colony P-Elimination System Hexaflumuron
1994-1995:Structure1. 
Structure 1 is a home of slab construction with ca. 215M2. One year prior to Sentricon* installation, the home was treated with Isofenphos. Upon initial inspection, no termites were encountered around the foundation of the home although extensive termite damage could be seen. Termites were discovered in wood debris near the home. Sixteen Sentricon stations were installed around the home on May 4th, 1994. Stations were spaced ca. 14m apart.

Termites found 2 of the 16 stations within the first month. As a result, two bucket/block traps were installed near the attacked stations on June 1, 1994 (Table 3). Both traps were inspected on June 29th, and both were attacked by termites. Another Sentricon station was attacked so another bucket/block trap was installed on June 29th, The wood block was returned to the laboratory for separation. After the block of wood was disassembled, the termites engaged in mortal combat among themselves. Of the 2000+ termites recovered from the wood block, only 150 termites were marked with Nile Blue A. The marked termites were released on the block of wood on July 8th 1994.

Three stations were baited for termites during the July visit (Table 4). Baitubes remained in place for four months with over 2.5 Baitubes being consumed. Feeding occurred primarily at two stations. Once baited, one station had a Baitube present for 8 of the remaining 10 months of the year. After the contents of 1.78 Baitubes had been consumed during the first two months, less than Q. 10 Baitubes were consumed during the rest of the year. Termites were encountered at one and two stations during the April and May visits, respectively. Termite activity on the wood blocks in the bucket traps indicated that termites were present almost continuously from June 1st, 1994 through May 11, 1995.

Termites have not been controlled.Although  termites fed on the bait and then were not detected for a period of time, they came back. Termites remained on the wood block for most of the year, and termites swarmed after the April inspection.

Structure 2. Structure 2 is a home of pier and beam construction with ca. 110m2. Termites had swarmed the year before the study started (1993). Swarmers were identified as termites, but no treatment was performed at the time. Upon initial inspection, no termites were encountered around the foundation of the home. The crawl space under the home was sealed off and too low for thorough inspection. No alternative food sources were identified near the home. Fifteen Sentricon stations were installed around the home on May 4th, 1994. Stations were spaced ca. 10m apart.

Termites were encountered only once, during the September visit (Table 4). A bucket/block trap was installed, but termites never attacked the wood block in the trap (Table 3).

Since termite baits were never installed, baiting can not be evaluated. It is speculated that the termite colony is rather small because swarming did not occur on a yearly basis. The Sentricon monitoring system indicated that termites were in the area, but the termites did not encounter the monitoring stations at high enough levels or frequency for baiting to be initiated.

Structure 3. Structure 3 is a home of pier and beam construction with ca. 105m2 . No termite treatment has been made in the recent past. Upon initial inspection, termites were encountered in many locations in the backyard (under cardboard debris and wood branches). Termites were found along the foundation (back steps) during the initial inspection. Seventeen Sentricon stations were installed around the home and were spaced about 10m apart.

Termite activity was recorded at 5 of the 17 stations during the year. Bucket/block traps were installed at the same time as the Sentricon stations because termites were present in the nearby vicinity. Termites attacked four stations within one month of installation. Termites attacked two of three wood blocks within two to three months (Table 3). After marking 2753 termites with Nile Blue A, the first Baitube was placed during the September visit (Table 4). Two other stations received Baitubes during the year. Total bait consumption for the year was estimated to be about 20% of one Baitube.

Termites have not been controlled. Termites encountered the monitoring stations, but fed on very little bait. Termites remained on wood blocks for almost year. Additionally, swarm tubes appeared from the eaves at the back right corner of  the home during April and May.

Structure 4. Structure 4 at the back right corner is a commercial site with three buildings, designated A, B, and C. All three structures are of pier and beam construction. Building A and B are portable buildings with ca. 57 and 27m2, respectively. Building C is a renovated home converted to a business with ca. 158m2 . Building A and C have siding which did not permit inspections underneath. Building was open so visible inspections were possible

Table 3. Termite activity at wood blocks placed around structures in conjunction with Sentricon stations during 1994-1995 & 1995-1996.

Termites swarmed from the front door frame of building A during the spring of 1994. Inspection under building B found termite tubing in several location. No evidence of termites was observed around the foundation of building C; however, termites were observed in wood beams holding up the porch. No professional termite control has been performed at this site for several years. No alternative food sources were noted in the nearby area. Nine, seven and fourteen Sentricon stations were installed around building A, B and C, respectively. Spacing between stations around building A and B was ca. 10m, while spacing between stations around building C was about 15m.

Termites attacked seven Sentricon stations within the first month of placement, and stations around all three buildings were attacked. Four bucket/block traps were placed at stations with high numbers of termites. Within two weeks, three of the four wood blocks were attacked by termites (Table 3). Two blocks of wood were recovered and returned to the laboratory for termite extraction. After marking the termites, ca. 4319 and 3750 termites were returned to their respective locations at building B and C where they were collected. Six Baitubes were placed during July and August (Table 3). Practically all bait consumption occurred during the month of August. Total estimated bait consumption at buildings A, B and C was 100 (one complete Baitube, 280 (almost three complete Baitubes) and 80% (almost one complete Baitube ), respectively. Of the four wood blocks placed around Buildings A, B & C, three blocks showed termite activity during the year. Locations where termites were collected, marked and released (blocks #2 and #4) showed activity during July and August. After which time, no termite activity was detected for the rest of the year. One wood block (#3) had termite activity continuously throughout the year. This bucket/block trap was located at building C on the opposite side of block #4. Even though Baitubes” were placed twice in the station by block #3, little bait was consumed either time.

It appears that control was achieved at buildings A and B. After a couple months of baiting at these buildings in which several Baitubes” were consumed, presence of termites was not detected for the remainder of the study. Furthermore, termites did not swarm during the spring of 1995. Although termites fed on some bait at building C, termites remained on block #3 throughout the year. It appears that either a partial reduction in the size of the colony occurred, or that two different termite colonies were encountered. The group of termites on one side of the building appears to have been eliminated, however, the group on the opposite side of the building continues to be active.

Table 4. Summary of 1994-1995 field,results using Sentricon stations around structures in Texas.

Asterisk indicates termites were encountered at one station. Station was not baited because termites never attacked the bucket/block trap for coloration.

Structure 5. Structure 5 is a home of slab construction with ca. 90M2. No professional control had been done for several years. Upon initial inspection, termites were found along wood borders of flower beds in the front of the house. The borders were within 0.5m of the foundation. No termites were observed around the foundation. Termites had swarmed in the spring of 1994 and alates were collected along the sill of the front porch window. Thirteen Sentricon stations were installed around the home and were spaced about 10 m apart.

Termite activity was recorded at two stations during the year. Termites were encountered within two months after stations were installed. One bucket/block trap was installed and was attacked within one month (Table 3). After marking, ca. 2182 termites were released. Baiting began in September and continued throughout the year (Table 4). However, termites only consumed about 10% of one Baitube. Termites were active in the wood block from July through October and again during March and April. Termites could be seen in foraging tubes along side the front of the house throughout most of the year.

Termites were not controlled. Termites consumed only I0%of one Baitube and remained on the wood,block for many months. Even when the termites disappeared  from the block of wood, termites were present along the right front side of the home. Termites built a foraging tube along the frame and if broken, termites could be seen. The study at Structure 5 ended prematurely (one month) because the home was sold.

Structure 6. Structure 6 is a home of slab construction with ca. 213 sq. ft. Termite swarming occurred in the bathroom/wash room during the spring of 1994. No known termite control had been done on this home. Upon initial inspection, no termites were encountered around the foundation of the home. No alternative food sources were noted in the surrounding area. Fourteen Sentricon stations were installed around the home and were spaced about 14m apart.

Two Sentricon stations were attacked within one month of installation. Two bucket/block traps were installed and one wood block was attacked the next month (Table 3). After ca. 1454 marked termites were released in July, baiting began (Table 4). A total of four Sentricon stations were baited, but bait consumption was low, a total of only 20% of one Baitube. Termites remained on the wood block from June through August, at which time, they were not detected again during the year.

It is difficult to determine if the termites have been controlled. It appears that the colony of termites was fairly small even though they attacked four Sentricon stations at four distant points fairly quickly. Termite swarming did not occur during the spring of 1995. Control was doubtful because of the low amount of bait consumed.

Structure 7. Structure 7 is a home of slab construction with ca. 137m2 . It had been treated for termites yearly for the past three years. The home was treated with foam in 1993. Upon initial inspection, no termites were encountered although, termite damage was readily apparent. Sixteen Sentricon stations were installed around the home and were spaced ca. 10m apart.

Termites attacked six Sentricon stations within one month. Three bucket/block traps were installed during June (Table 3). Two wood blocks were attacked within one month. After marking, ca. 2209 termites were released at the location they were collected. At the same time, I I of the 16 stations were baited (Table 4). Numbers of termites placed in the Baitubes for recruitment purposes ranged from 20 to over 200 individuals. After two weeks, Baitubes were checked and 9 of the 11 Baitubes needed to be replaced. Amount of bait consumed during the two week period ranged from 50 to 97% of one Baitubes. As with wood stakes, termites (25 to 125) were collected out of each Baitube and placed in the new Baitube for recruiting purposes. While placing the termites in the new Baitubes, many marked termites were encountered. Six of the nine stations receiving new Baitubes had marked termites.

During the next visit (August), I I new Baitubes were placed in the Sentricon stations. Termites consumed between 70 and 100% of these Baitubes. Only 2 of the 11 stations had termites present. At both stations, over 100 termites were placed in the new Baitube for recruitment purposes. Termites were found on only two blocks. During the September visit, only 2 of the 11 Baitubes had signs of feeding. Bait consumption was low, less than 5% in each Baitube. No termite activity was detected at any of the bucket/block traps. After the October visit, no termite activity was detected at any of the Sentricon stations or bucket/block traps for the rest of the year.

Termites appeared to have been controlled. No swarming occurred during the spring of 1995. The dramatic decrease in the termite population was indicative of how hexaflumuron brings about termite control. Termites fed on a large quantity of bait (over 17 Baitubes), and after a couple months of feeding, they disappeared. Termites that were brought in from the field behaved in a similar manner, only it took a month longer for the termites to die. The longer time for the termites to die in the laboratory can be attributed to the lower temperature.

1995-1996: Structure 1: Seventeen additional Sentricon stations were placed around Structure1 making a total of 33 Sentricon stations (Table 5). Termites continued to attack the stations placed during 1994 through 1995-1996. Total bait consumption was low, only 0.18 of one Baitube. The new Sentricon stations placed in 1995 were attacked only once throughout the year. However, over one complete Baitube (1.30) was consumed by termites. Termites were found on wood blocks from June through September, 1995, after which time, they were not encountered again.

Termites have not been controlled at Structure 1. Although they have not been encountered at the bucket/block traps since September, termites have encountered Sentricon stations at other locations around the home, and one station was attacked during the April visit.

Table 5. Summary of 1994-19958,1995-1996 field results using Sentricon stations around structures in Texas.

Notes: Hyphenated numbers indicate that termites were present at a station but numbers were not sufficient for baiting purposes. Asterisks indicate that founding pairs of termites were encountered in a station. Number of asterisks indicate number of founding pairs.

Structure. 2: An additional 10 Sentricon stations were placed at Structure 2 making a total of 25 Sentricon stations. Termite activity was not detected at any station until the April visit. One station, placed June 1995, was attacked by twenty termites. Because the number of termites was low, a Baitube was not installed at the station. During the May inspection, termites were encountered at the same station as in April as well as another Sentricon’s station, however, no Baitubes were placed because the study was being terminated at this structure.

As in 1994-1995, results for 1995-1996 were not obtained. Since no Baitubes were installed in the Sentricon stations, an evaluation of hexaflumuron could not be made. However, it appears the Sentricon “system” failed to produce results. Because this structure had termites, and the number of Sentricon’t stations around the home was high (spaced every five meters), termites should have come in contact with more of the stations.

Structure 3: Seven additional Sentricon stations were installed when the 1995-1996 study started (Table 5). An additional two stations were added during the year. As a result, a total of 26 Sentricon stations were around Structure 3. Termites attacked two of the Sentricon stations placed during 1994 from August through November, 1995; however, bait consumption was low. No termites were encountered throughout the year on the new Sentricon stations. Termites were present on the wood blocks (# 1 and #3) for several months of the year (Table 3). The last termite activity was recorded in March 1995.

Termites were not controlled at Structure 3. For all practical purposes, no bait consumption occurred during the 1995-1996 year, and termites remained on the wood block in the bucket traps.

Structure 4: Buildings A & B were portable buildings. At the beginning of the 1995 study, both buildings were relocated about 20 in away. Twelve Sentricon stations were installed around these buildings. Because termites were being encountered only at one location at building C, only two new stations were installed. Termites were encountered once around building A & B (Table 5). One Baitube was placed at the station, but little to no feeding occurred. At building C, no termite activity occurred at any Sentricon’t station until the April inspection. One station was attacked, but the number of termites present was insufficient to place a Baitube. Termites were not encountered at either block placed around building C.

It was difficult to ascertain whether the termites at buildings A & B and building C were controlled. It appeared that some degree of suppression occurred at buildings A & B during the 1994-1995 year. Because the buildings were moved, a new colony may have been encountered. In any event, termites were encountered, and because little bait was consumed, probably no suppression occurred in this new colony. At building C, the one station attacked by termites occurred in April and was within 15 m of wood block #3 which had termites on it throughout the 1994-1995 year. It was not known whether these termites are from the same colony that was present in 1994 or from a new colony.

Structure 5: Dropped from study in April 1995.

Structure 6: In 1995, seven addition Sentricon stations were installed near the stations that were attacked during 1994. A total of 21 stations monitored Structure 6. There was no termite activity at any station or any bucket/block trap throughout the 1995-1996 year (Tables 3 & 5).

It appeared that the termite population may have been suppressed. Even though no termite activity occurred during 1995-1996, termites were encountered four distant points during the 1994-1995 year. Because little bait was consumed during 1994-1995, it was not known whether control or suppression occurred. The inability to detect termites using 21 Sentricon stations placed in locations where termite activity has occurred may indicate a failure in the Sentricon system to detect termites (similar to the results obtained at Structure 2).

Structure 7: No additional Sentricon stations were installed around Structure 7. During the 1995-1996 year, the original station were monitored for the return of termite activity. No termite activity was encountered at any Sentricon station or bucket/block traps (Tables 3 and 5).

It appeared that the colony of termites at Structure 7 were eliminated. Many Sentricon station were attacked. Over 17 Baitubes (<500 grams of hexaflumuron) were fed upon by termites. No termite activity has been detected at Structure 7 for 1 1/2 years.

Structure 8: It took only one month for termites to attack three of the Sentricon stations. Two bucket/block traps were installed at locations of highest termite activity (Table 3).- Three Baitubes were placed during the July visit (Table 5). Two of the three Baitubes had high bait consumption (75% of one Baitube). Bait consumption by termites continued for several months and then subsided. Additional Sentricon stations were placed during the December, February, March and April visits because termites were encountered either at stations or in the structures. Termites were encountered on wood blocks continuously from August through April (Table 3).

Termites were not controlled at Structure 8. It appeared that there are many foraging sites around these structures. Bucket/block traps were installed at the same locations where the termites consumed the majority of the bait. Termites remained on one block until March, and returned to the second block during the April visit. Because of the close proximity of Baitubes and bucket/block traps, it appeared that hexaflumuron had little to no effect on the termite population.

DISCUSSION

The bait containing  hydramethylon developed by American Cyanamid Company, did not appear to control termite populations at any test location. Of the four structures studied in 1994-1995, suppression of termite populations appeared to have occurred at two structures (Structures 1 and 3). However, termites were still present at Structures 1, 3, and 4  when the study  was terminated.

American Cyanamid Company made several improvements in their delivery system during the 1995-1996 study. One major improvement was the addition of a housing unit that allows for the easy removal/ replacement of bait cartridges. The housing unit minimized the disturbance to the surrounding areas allowing for the establishment of continual feeding sites. The bait cartridge was re-designed and now has thin slits in its side that enables termites to enter the bait cartridge but deters other organisms from tunneling in the cartridge. The last modification in the delivery system was that active bait cartridges were placed in the housing units continuously so when termites feed, they will consume active bait.

During 1994-1995. termites fed intermittentIv on baits. Termites would feed on the placebo bait, but would not feed on the placebo bait, but would not feed, to any great extent, on the active bait. in 1995-1996 when hydramethylnon bait was placed in the wood stakes, C.formosanus abruptly ceased feeding on the wood stakes. These occurrences indicated that both Reticulitermes spp and C. formosanus were capable of detecting hydramethylnon and thus avoided the bait. A more palatable/preferred material is needed so that termites will feed continuously on baits.

During 1994-1995 and 1995-1996, termites encountered wood stakes more frequently than they encountered bait cartridges at all structures. Therefore, it appeared the termites had a distinct preference for feeding on natural products as opposed to a formulated product. If either the wood stakes themselves are dipped/soaked in hydramethylnon or the cardboard strips that are placed in the wood stakes are so treated, the termites may acquire more toxic material to reduce/control the termite colony. If the termites are able to detect hydramethylnon, this procedure would not work. Therefore, studies should be conducted to determine if and at what dosage levels hydramethylnon can be detected by termites.

The bait containing hexaflumuron, develop by DowElanco, appeared to have achieved control at one of the eight structures (Structure 7). It appeared that termite populations may have been suppressed at Structure 6 and possibly building A and B of Structure 4. Termites were not controlled at Structures 1, 2, 3, 5, 8 or at building C at Structure 4. It appears the ability of hexaflumuron (or the Sentricon system) to control a termite infestation may lie in the size of the termite population; the larger the colony size the better the chances for colony suppression.

Termites were capable of locating the Sentricon stations rapidly and reflects station design. Termites located Sentricon stations within one month after installation at six of the eight test locations. Termites required two months to encounter a Sentricon station at another test location and required four months at the last test location. Collectively, termites attacked 18.7% of the monitoring stations during the first year they were installed around structures. Even though the termites found the stations quickly, they may not continually forage to a specific station. The attack rate dropped to 7.6% for these monitors during the second year. This emphasizes the importance of control stations (bucket/block traps). Lack of termite activity (or our ability to detect it) does not necessarily indicate that termites have been controlled. Blocks of wood at Structures 1, 4 (building C) and 5 indicated that termites were present even though termites were not encountered at the Sentricon stations. Therefore, independent monitors (wood blocks or wood stakes) need to be placed at each structure to help assess whether termite control has been achieved.

The addition of more Sentricon stations around each structure had no apparent effect on termite encounters at structures started in 1994 and continued through 1996, only one structure had the newly placed Sentricon stations attacked. And, only one station at that structure was attacked. The attack rate of additional stations placed around structures already being monitored was 2.2%. The Sentricon stations placed around the new (eighth) structure were attacked quickly, three stations within the first month. However, after the initial attack, termites only attacked one other station during the rest of the year. From our data, it appears that increasing the number of Sentricon stations around a structure will not increase the number of termite encounters with stations. As a result, using the number of stations attacked after a couple of months after installations, may indicate whether control can be achieved and how fast control may be achieved through the use of the Sentricon elimination system.

A very interesting event occurred during the April and May visits in 1996. It appeared that the Sentricon stations around structures offered a location conducive for colony founding. In Table 5, the number of founding pairs found during the April and May inspections are indicated with an asterisk. Founding pairs were encountered six times at four of the seven test structures in April and in May. As an added note, more than one founding pairs occurred together at stations. Of the six occurrences in April, one pair of primary reproductives were encountered four times, two pairs of primary reproductives were encountered one time and three pairs of primary reproductives were encountered one time. All founding pairs were located at the bottom and between the wood stakes in the stations. Therefore, if the wood stakes were not removed for inspection, the founding pairs would never have been encountered.

Because termites are cryptic individuals, control is never certain. If the amount of bait needed to control a certain number of termites is known, it would help indicate whether enough bait has been consumed to reduce field populations. Field populations can be estimated into small, medium, large, mega-colonies using mark-release-recapture studies or simply by the number of stations attacked, time to attack and the number of termites attacking each station. Seventeen Baitubes was probably an overkill. But, it was probably the overkill that eliminated the colony at Structure 7. Fungus, bacteria and mites develop on dead and dying termites rendering the entire foraging network of the colony unsuitable for survival. As a result, all termites (including the reproductives) died. Furthermore, studies are needed to determine the role trophallaxis and cannibalism play in distributing baits (both hydramethylnon and hexaflumuron) throughout a colony.

More research is needed to “make” these systems work. Since hexaflumuron is a IGR, what is the effect of hexaflumuron on reproductives? Since they do not molt, hexaflumuron will not kill reproductives. Since the reproductives are capable of substantial movement (being physogastic does not restrict mobility), is the colony just suppressed until numbers can build back up or does hexaflumuron have an effect on the egg or sperm production of both? Lastly, methods to enhance the delivery, the appeal of the bait and the retention of termites at feeding sites needs investigating for all baits.

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