Determining the most effective concentration of cypermethrin and the appropriate carrier particle size for fire ant (Hymenoptera: Formicidae) bait

BACKGROUND: The purpose of this study was to determine the most effective particle size of DDGS (distiller's dried grains with solubles) as fire ant bait carrier, as well as the most effective concentration of cypermethrin as a toxicant against the red imported fire ant (RIFA) Solenopsis invicta Buren under laboratory conditions. RESULTS: The DDGS particle size did not affect the fire ant's preference for the bait, but it did affect the mass of DDGS being carried back to the nest. The size of the DDGS particles and the mass of DDGS being carried back to the nest were positively correlated. The most efficient particle size of DDGS was 0.8–2 mm. The concentration of cypermethrin has a specific range for killing fire ants in an efficient manner. Neither a very low nor a very high concentration of cypermethrin was able to kill fire ants efficiently. The most effective concentration of cypermethrin was 0.13% in DDGS when mixed with 15% shrimp shell powders and 11% soybean oil. CONCLUSION: Based on its ability to kill fire ants when mixed with cypermethrin, as well as the advantage of having a larger area coverage when sprayed in the field, DDGS as the carrier and cypermethrin as the toxicant can be considered to be an efficient way to prepare fire ant bait for controlling fire ants in infested areas. Copyright © 2012 Society of Chemical Industry     

Efficacy of Beauveria bassiana against the red imported fire ant, Solenopsis invicta (Hymenoptera: Formicidae), in Taiwan

BACKGROUND: Combining biological control and chemical control could be used for controlling red imported fire ant (RIFA), Solenopsis invicta, more effectively. Beauveria bassiana F256, a local strain from Taiwan, was evaluated for its efficacy in the control of S. invicta under both laboratory and field conditions. RESULTS: The efficacies of different doses of B. bassiana (Bb) using direct application and bait formulation methods were compared. The number of RIFA workers killed by the direct application of Bb or by bait were significantly higher than those of the control, with different rates of efficacy under laboratory conditions. Under field conditions, the direct application of Bb into RIFA mounds was more efficient in inactivating the mounds than the bait application. CONCLUSION: It was shown that B. bassiana is able to control S. invicta under both laboratory and field conditions and can be used as a biocontrol agent against RIFA in Taiwan. Copyright © 2011 Society of Chemical Industry     

Development of strategies for monitoring indoxacarb and gel bait susceptibility in the German cockroach (Blattodea: Blattellidae)

BACKGROUND: Advion^® cockroach gel bait (6 g kg^?1 indoxacarb) is in widespread use for Blattella germanica (L.) control in the United States. However, baseline susceptibility levels to indoxacarb in German cockroach field populations are not known. Hence, this research sought to develop monitoring strategies to estimate the susceptibility of German cockroach populations to indoxacarb. RESULTS: Four bioassays were evaluated: topical lethal dose (LD), formulated gel bait lethal time (LT), vial lethal concentration (LC) and gel bait matrix LD. Of these methods, the vial LC and gel bait matrix LD bioassays were the most economical and relevant assessment strategies. For indoxacarb susceptibility monitoring, a two‐tiered approach was developed that utilizes diagnostic concentrations and doses in vial LC (30 and 60 µg vial^?1) and gel bait matrix LD (1.0, 1.5 and 2.5 µg insect^?1) formats. CONCLUSIONS: A two‐tiered susceptibility monitoring strategy was developed that includes testing field populations at diagnostic concentrations and doses in first‐tier vial LC bioassays and second‐tier gel bait matrix LD bioassays. The vial method facilitates rapid identification of field strains with reduced susceptibility. The feeding bioassay effectively simulates field exposure to Advion^® and therefore has utility for secondary confirmation of susceptibility shifts and identification of behavioral resistance (i.e. bait aversion). Copyright © 2010 Society of Chemical Industry     

Toxicity of formic acid to red imported fire ants, Solenopsis invicta Buren

BACKGROUND: Ants often compete with other ants for resources. Although formic acid is a common defensive chemical of formicine ants, it does not occur in any other subfamilies in Formicidae. No information on toxicity of formic acid to red imported fire ants, Solenopsis invicta, is available. This study examined its contact and fumigation toxicity to S. invicta in the laboratory. RESULTS: In a contact toxicity bioassay, 24 h LD₅₀ values of formic acid for workers ranged from 124.54 to 197.71 µg ant⁻¹. Female alates and queens were much less sensitive to formic acid than workers. At a concentration of 271.72 µg ant⁻¹, which killed 81.09 ± 16.04% of workers, the 24 h mortality was up to 39.64% for female alates and 38.89% for queens. In fumigation bioassays, 24 h LC₅₀ values ranged from 0.26 to 0.50 µg mL⁻¹ for workers, 0.32 µg mL⁻¹ for male alates and 0.70 µg mL⁻¹ for female alates. Complete mortality (100%) in queens occurred 24 h after they had been exposed to 1.57 µg mL⁻¹ of formic acid. At a concentration of 2.09 µg mL⁻¹, KT₅₀ values ranged from 23.03 to 43.85 min for workers, from 37.84 to 58.37 min for male alates, from 86.06 to 121.05 min for female alates and from 68.00 to 85.92 min for queens. CONCLUSION: When applied topically, formic acid was significantly less toxic than bifenthrin to red imported fire ants. Although its fumigation toxicity was lower than that of dichlorvos, formic acid had about an order of magnitude higher toxicity to S. invicta than to other insects studied so far. It may be worth investigating the use of formic acid for managing imported fire ants. Published 2012 by John Wiley & Sons, Ltd.     

0.2%高效氯氰菊酯粉剂对田间红火蚁种群数量及蚁巢迁移的影响

为科学评价触杀性粉剂对红火蚁Solenopsis invicta Buren的防治效果,利用0.2%高效氯氰菊酯粉剂对田间红火蚁蚁巢进行单蚁巢处理,分析粉剂施用剂量和次数对田间红火蚁种群数量及蚁巢迁移的影响。结果表明,触杀性粉剂处理可在短期内显著降低红火蚁的蚁巢数量和工蚁诱集数量,50 g/巢和100 g/巢处理1 d后,蚁巢数量降幅分别达55.17%和66.04%,工蚁诱集数量降幅分别达31.79%和51.95%,但5～9 d后基本恢复至处理前水平,第21天蚁巢增加率达86.21%和37.74%,持效性较差。增多粉剂施用次数同样也只能在短期内压低红火蚁的蚁巢数量和工蚁诱集数量,施用1、2和3次粉剂1 d后蚁巢数量降幅分别达61.44%、76.82%和80.79%,工蚁诱集数量降幅分别达55.40%、47.21%和28.36%,随着时间延长,蚁巢数量和工蚁数量很快恢复。虽然随着施药剂量增加,蚁巢增加率和分巢率明显降低,新蚁巢出现时间略有延迟,新蚁巢的体积明显减小,但整体来看蚁巢数量仍呈上升趋势,新蚁巢出现的距离和方位也没有明显差异。表明粉剂防治仅可在短期内表面上压低红火蚁种群数量,即使...     

Combined use of a synthetic trail pheromone and insecticidal bait provides effective control of an invasive ant

BACKGROUND: Except for sex pheromones, use of pheromones in pest management has been largely unexplored. A high concentration of trail pheromone disrupts ant trail following and foraging, and thus synthetic trail pheromone can be a novel control agent for pest ants. In this study, a year‐long treatment of small areas (100 m² plots of urban house gardens) with synthetic trail pheromone, insecticidal bait or both was conducted to develop a novel control method of the invasive Argentine ant Linepithema humile (Mayr). RESULTS: The ant population could be maintained lower than or similar to the initial level only by combined treatment with synthetic trail pheromone and insecticidal bait. Actually, the ant population was nearly always lowest in combination treatment plots. Throughout the study period, the ant population in plots treated with either one of synthetic trail pheromone or insecticidal bait remained similar to no‐treatment plots. CONCLUSIONS: Combination treatment may be a more effective and environmentally friendly method for controlling invasive ants than conventional methods. Extermination of ants by insecticidal bait and inhibition of re‐infestation by pheromone may be the mechanism of the combination effect. This is the first study to show a significant effect of synthetic trail pheromone on ant population. Copyright © 2011 Society of Chemical Industry     

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants,Brachyponera chinensis

BACKGROUND

The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control.

RESULTS

The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days.

CONCLUSION

The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Aerosol delivery of trail pheromone disrupts the foraging of the red imported fire ant,Solenopsis invicta

BACKGROUND: The fire ant, Solenopsis invicta, is one of the most aggressive and invasive species in the world. The trail pheromone Z,E‐α‐farnesene (91% purity) was prepared, and disruption of worker trail orientation was tested using an ethanol‐based aerosol formulation presenting a single puff of this compound by airbrush and compressed air. Trail‐following behaviour was recorded by overhead webcam and ants digitised before and after presentation of the aerosol treatment at four rates (1.6, 16, 160 and 1600 ng cm^?2). RESULTS: Ants preferred 110 ng cm^?1 over 11, 1.1 and 0.11 ng cm^?1 for trail following. Within seconds of presentation of 1600 ng cm^?2, the highest dose tested, trail disruption was observed. Disruption was evident as reduced arrival success and reduction in the trail integrity statistic (r²), as well as increased deviation from the trail (deg). The distribution of walking track angles was also flattened. CONCLUSIONS: The feasibility of using aerosol for delivery of trail pheromone was demonstrated, but the need for high purity combined with the difficulty of commercial supply makes this technique impractical. However, the commercial production of Z,E‐α‐farnesene of high purity by industrial biotechnology or from (E)‐nerolidol may be possible in future, which would facilitate further development of trail pheromone disruption of S. invicta. Copyright © 2012 Society of Chemical Industry     

A laboratory evaluation to determine the compatibility of microbiological control agents with the pollinator Bombus terrestris

BACKGROUND: This study was undertaken to identify any potential adverse side effects of the use of seven microbiological control agents (MCAs) on the bumblebee, Bombus terrestris L., in the context of combined use in integrated pest management (IPM). AQ10^® (Ampelomyces quisqualis), Binab‐T‐vector^® (Hypocrea parapilulifera + T. atroviride; 1/1), Prestop‐Mix^® (Gliocladium catenulatum J1446), Serenade^® (Bacillus subtilis QST713), Trianum‐P^® (Trichoderma harzianum T22), Botanigard^® (Beauveria bassiana GHA) and Granupom^® (Cydia pomonella granulovirus), comprising five biofungicides and two bioinsecticides, were investigated. Bumblebee workers were exposed under laboratory conditions to each MCA at its maximum field recommended concentration (MFRC) via three different routes of exposure: dermal contact and orally via either treated sugar water or pollen. RESULTS: The tested MCAs were found to be safe for workers of B. terrestris, with the exception of Botanigard^® and Serenade^®. Exposure to Botanigard^® via contact at its MFRC caused 92% mortality after 11 weeks, while the 1/10 MFRC killed 46% of exposed workers. For Serenade^®, topical contact and oral delivery via sugar water resulted in 88 and 100% worker mortality respectively. With lower concentrations (1/2, 1/5 and 1/10 MFRC) the toxicity decreased, but the effect depended on the route of exposure. In addition to lethal effects, nests were also evaluated for sublethal effects after treatment with the seven MCAs at their respective MFRCs over 11 weeks. In these bioassays, only Botanigard^® and Serenade^® gave rise to a significant (P < 0.05) decrease in drone production. Sublethal effects on foraging behaviour were also evaluated, and only Botanigard at its MFRC delivered via treated sugar water induced negative effects. CONCLUSION: The results demonstrated that most of the MCAs tested can be considered safe for use in combination with B. terrestris, based on the International Organisation for Biological Control of Noxious Animals and Plants (IOBC) classification. However, some can be harmful, such as the biofungicide Serenade^® and the bioinsecticide Botanigard^®. Therefore, it is recommended that all should be tested before use in combination with pollinators. In this context, it is also advisable that these MCAs should be evaluated in more realistic field situations for the assessment of potentially deleterious effects on foraging behaviour. Copyright © 2009 Society of Chemical Industry     

Effects of piperidine and piperideine alkaloids from the venom of red imported fire ants,Solenopsis invicta Buren,on Pythium ultimum Trow growth in vitro and the application of piperideine alkaloids to control cucumber damping‐off in the greenhouse

BACKGROUND: Pythium ultimum is a plant pathogen that causes significant yield losses on many economically important crops. Chemical treatment has been used for disease control. In searching for alternatives, venom piperidine and piperideine alkaloids from red imported fire ants were tested against P. ultimum in vitro, and piperideines were employed to control cucumber damping‐off in the greenhouse as drench treatments. Results Piperidine and piperideine alkaloids of the red imported fire ant significantly inhibited mycelium growth of P. ultimum. Piperidine alkaloids were stable at both room and elevated temperatures. The inhibitory activity positively correlated with the concentrations of piperidine alkaloids in the medium, and the EC₅₀ = 17.0 µg ml^?1. Germination of sporangia of P. ultimum was negatively correlated with the concentrations of piperidine alkaloids in the medium, and the EC₅₀ = 12.3 µg ml^?1. The piperideine alkaloid drenching treatment significantly improved seedling emergence and seedling height of cucumber. CONCLUSION: This is the first report describing the use of venom alkaloids from the red imported fire ant to inhibit P. ultimum in the laboratory and the application of piperideine alkaloids to control damping‐off disease caused by P. ultimum in the greenhouse. These findings may lead to the development of a new group of fungicides. Copyright © 2012 Society of Chemical Industry     

硫氟磺酰胺、氟虫腈和苯氧威3种饵剂对红火蚁的防效初探

在红火蚁严重发生地区进行的药效试验表明,0.5%硫氟磺酰胺饵剂投放后15d药效开始发挥,25d后处理蚁巢全部死亡,药后70d调查结果显示,其对红火蚁的校正防治效果高达94.1%;0.001%氟虫腈饵剂撒施后15d开始发挥药效,30d后蚁巢中无工蚁活动,药后70d调查显示其对红火蚁的防治效果为90.9%;0.5%苯氧威饵剂撒施后40d,在蚁巢中仍能监测到工蚁的活动,70d后调查结果表明其对红火蚁的防治效果为84.9%。统计分析结果说明,0.5%硫氟磺酰胺饵剂和0.001%氟虫腈饵剂对红火蚁的防治效果好于0.5%苯氧威饵剂。由于0.001%氟虫腈饵剂和0.5%苯氧威饵剂是实验室临时配制,虽然其对红火蚁的诱食性较差,但仍能表现较好的防治效果。0.5%硫氟磺酰胺饵剂和0.001%氟虫腈饵剂可以用于红火蚁的防治,0.5%苯氧威饵剂配方需要进一步改进。     

11种杀虫剂对草皮中红火蚁的检疫除害效果

本文试验了11种杀虫剂对草皮中红火蚁的检疫灭除效果。结果表明,40%毒死蜱乳油30000倍液2、%阿维菌素乳油30000倍液、80%敌敌畏乳油6000倍液4、.5%高效氯氰菊酯乳油3000倍液浓度可完全杀死红火蚁,且对草皮生长没有影响,满足检疫处理要求;其余7种不能达到快速灭除草皮中红火蚁的要求。同时发现,草皮中的红火蚁数量与实际诱集到的数量之间关系符合模型Y=0.0032X-0.59(R2=0.9647,P=0.01)。     

Control of Solenopsis invicta with delayed-action fluorinated toxicants

The fire ant, Solenopsis invicta Buren, was accidentally imported into the southern United States and has become a serious medical and agricultural pest of nine southeastern states and Puerto Rico. For a bait toxicant to be effective in fire ant control it must have delayed activity over a wide range of concentrations. Less than 1% of the 7500 compounds screened since 1958 has had delayed action. This paper describes several classes of fluorinated compounds that exhibit delayed activity. These compounds are used to illustrate the following three approaches to the discovery of delayed-action toxicants: (a) random screening of compounds for delayed action; (b) design of delayed activity through the synthesis of pro-insecticides; and (c) serendipity. As a result of these investigations two new classes of insecticides were discovered. A compound from one of these classes (tetrahydro-5,5-dimethyl-2(1H)-pyrimidinone (3-(4-(trifluoromethyl)phenyl)-1-(2-(4-(trifluoromethyl)phenyl)-ethynyl)-2-propenyl-idene) hydrazone, has been commercialised, while one or more compounds from the second new chemical class (fluorinated sulphonamides) are under development. Fluorinated delayed-action insecticides have made significant contributions to current fire ant control and will no doubt play a role in the future.     

Determination and management of weaver ant,Oecophylla smaragdina (Fabricius) (Hymenoptera: Formicidae), marks on mango fruit in the Northern Territory of Australia

Weaver ants, Oecophylla smaragdina (Fabricius), can be used to manage insect pests in mango orchards in the Northern Territory of Australia, but previously unidentified black marks on fruit can reduce fruit marketability. To determine the cause of the marks, and to reduce the number of fruits by such marks, field experiments were conducted in three mango orchards in the Darwin area of Australia in 2001 and 2002. The results from netting bag-rearing showed that the black marks on fruit were due to the deposition of weaver ant formic acid, and fighting between weaver ant colonies was the major cause of the deposition. In treatments without isolation of weaver ant colonies, an average of 4.8% of fruits with the ant marks were downgraded, and this damage level was reduced to 2.1% in treatments with isolation of weaver ant colonies. Because of weaver ant foraging behaviour, this small proportion of downgraded fruits was unavoidable, but the benefits of the ants as biocontrol agents against a range of pests outweighs the cost of the damage the ants cause.     

α -三联噻吩对红火蚁Solenopsis invicta觅食行为和触角功能的影响

通过研究光活化杀虫活性成分 α -三联噻吩( α -T)对红火蚁 Solenopsis invicta Buren工蚁觅食行为和触角识别功能的影响,探讨了光活化成分用于控制红火蚁的可行性。用Potter喷雾法将100 μg/mL的 α -T丙酮水溶液喷施于红火蚁中型工蚁体表,再经紫外(UVA)光照射30 min,在处理后5、10、15、20和30 min时,试蚁对火腿肠的识别率分别为20.00%、25.00%、38.33%、40.00% 和41.67%,对杀虫剂饵料的识别率分别为3.33%、0、0、3.33%和0,聚集率分别为17.50%、38.33%、 32.50%、45.00%和48.33%;经100 μg/mL的 α -T涂抹试蚁触角再经紫外光照处理30 min后,触角对丙酮反应的电位值为-0.177 mV,可正常行走的工蚁比率为75.00%;以100 μg/mL的 α -T涂抹试蚁触角并经紫外光照射30 min后10 h,红火蚁的死亡率为27.50%;上述结果均与 α -T黑暗处理、对照(CK)光照处理和CK黑暗处理结果差异显著。 α -T对红火蚁工蚁食物识别和探路行走能力均具有良好的光活化抑制作用,以其防治红火蚁具有良好可行性。     

Comparison of pheromone lures used in mass trapping to control the tomato leafminer Tuta absoluta (Meyrick, 1917) in industrial tomato crops in Kairouan (Tunisia)

An experimental trial of integrated pest management against Tuta absoluta (Meyrick) based on mass trapping with a density of 32 traps per hectare was conducted in a 5 ha open‐field tomato crop. During this trial, the efficiency of three brands of sex pheromone dispenser commercialized in Tunisia was tested. The ‘superdosed’ pheromone lure type TUA‐Optima^® (Russell IPM, Deeside, Flintshire, CH5 2LA, United Kingdom) loaded with 0.8 mg of synthetic pheromone was more attractive to males of T. absoluta, and these lures should be used with high populations. Standard lures Pherodis^® and TUA‐500^® containing 0.5 mg of pheromone were less attractive, and can be used in open‐field tomato crops with lower populations of T. absoluta. An assessment of the susceptibility of crop borders to T. absoluta, based on data collected from traps, revealed that levels of adult T. absoluta were similar between borders with either tomato or cereal crops. Particular attention should thus be paid to crop borders even when not adjacent to other tomato crops.     

Efficacy of attract‐and‐kill devices for the control of Ceratitis capitata

BACKGROUND: The control of Ceratitis capitata Wiedemann traditionally has relied on chemical control with organophosphate insecticides. The use of many of these substances has been banned by new European directives; therefore, the development of new control methods is essential to manage this pest. Bait sprays with spinosad, mass trapping and lure‐and‐kill techniques have been the base for new integrated pest management programmes. In this study, a 2 year field trial was conducted in two citrus areas to test the efficacy of attract‐and‐kill devices against mass trapping and spinosad‐plus‐bait treatments. RESULTS: The Magnet^® MED attract‐and‐kill device, Spintor^® treatments and mass trapping achieved good control of C. capitata populations, as confirmed by low percentages of damaged fruit in the assessments performed during the harvest period. On the other hand, fly population levels on plots treated with other attract‐and‐kill prototype devices increased more than threefold by comparison with the populations recorded in the rest of the treated plots. The same effect was observed for fruit damage, with 6–8 times less damage with Magnet^® MED and spinosad treatments, respectively, than with the attract‐and‐kill prototype devices. CONCLUSION: By using an effective attractant, conventional trapping systems can be replaced with cheaper and easier‐to‐handle attract‐and‐kill devices. The efficacy of these devices and their advantages over conventional mass trapping systems are discussed. © 2012 Society of Chemical Industry     

Pesticides

Abstract

The anticoagulant chlorophacinone was evaluated in the laboratory for the control of the gerbils Tatera indica Hardwicke and Meriones hurrianae (Jerdon), which are major pests of agricultural crops, grassland and reforestation projects in the arid zone of India. Millet and sorghum grain treated with chlorophacinone was offered in no‐choice feeding tests. The results showed that 100% mortality occurred after seven and five days with 0.0075% chlorophacinone and after three and four days with 0.01% chlorophacinone in T. indica and M. hurrianae respectively. The anticoagulant‐treated bait was significantly less palatable than untreated bait, except bait containing 0.0075% chlorophacinone to T. indica. It is concluded that 0.0075% chlorophacinone can be effectively used to control the gerbils, especially bait‐shy populations previously exposed to zinc phosphide bait. Chlorophacinone appears to give more effective control than warfarin and fumarin, and slightly less effective control than brodifacoum.     

氟磺酰胺毒饵使用量对红火蚁防治效果的影响

在确定了氟磺酰胺毒饵对红火蚁控制效果的基础上,就氟磺酰胺毒饵的使用量对红火蚁的控制效果进行了研究。结果表明:在5-25 g/巢的范围内,氟磺酰胺毒饵都可获得较好的防治效果,但防治效果及蚁巢的死亡程度会因施药量的不同而异。5 g/巢的剂量可在40 d内获得平均为96.7%的防效,但不能将所有的蚁巢杀死。10-25 g/巢的剂量可以在30-40 d内使蚁巢死亡,但蚁巢100%死亡所需的时间会因剂量的减少而延长。工蚁数量下降的程度不会因氟磺酰胺毒饵的使用量而产生差异。为此,建议在使用氟磺酰胺毒饵防治红火蚁时,可在10-25 g/巢的范围内根据蚁巢大小调整使用量。     

Effects of piperonyl butoxide and DEF on the metabolism of methoprene by the imported fire ant,Solenopsis invicta Buren

Studies are presented on the effects of two synergists, piperonyl butoxide and S,S,S-tributyl phosphorotrithioate, on the metabolism of methoprene [isopropyl (2E,4E)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate], an insect growth regulator, by the castes of the imported fire ant, Solenopsis invicta Buren. In adults, but not in larvae, pharate pupae, and pupae, piperonyl butoxide, a microsomal enzyme inhibitor, reduced methoprene metabolism by blocking O-demethylation. S,S,S-Tributyl phosphorotrithioate, an esterase and microsomal oxidase inhibitor, was most effective in reducing methoprene metabolism in larvae. In toxicity studies, against pharate pupae, the O-demethylated methoprene metabolite (alcohol-ester) was shown to be more toxic than methoprene. Synergists may be useful in bait formulations used for imported fire ant control to extend the effectiveness of methoprene.