Laboratory evaluations of insecticide product efficacy for control of Cimex lectularius

A susceptible, laboratory strain of bed bug, Cimex lectularius L., was used to determine the efficacy of insecticide products labeled or possessing a site label for bed bug control. Field strain bed bugs also were used to evaluate one insecticide product. The lethal time (LT),, values calculated for the laboratory strain bed bugs indicated that all of the pyrethroid products killed significantly faster than chlorfenapyr (0.5% [AIl; Phantom: BASF; LT50 = 10 d and 9 h). lamda-Cyhalothrin (0.03%; Demand CS; Syngenta) was the fastest acting insecticide (LT50 = 20 min), followed by bifenthrin (0.02% [AI]; Talstar One, FMC; LT50 = 53 min), deltamethrin (0.06% [AI]; Suspend SC; Bayer; LT50 = 61 min), and permethrin (0.05%; Dragnet SFR; FMC; LT50 = 88 min). The field strain bed bugs exposed to deltamethrin had an LT50 value of 14 day 8 h, indicating that the field strain was significantly less susceptible to deltamethrin than the laboratory strain. Chlorfenapyr exposure did not prevent the laboratory strain bed bugs from mating and laying eggs, nor did it prevent the eggs from hatching during the 2-wk exposure period. Surprisingly, none of the insecticides tested, including the pyrethroids, were repellent to laboratory strain bed bugs. Bed bugs rested on pyrethroid-treated panels and remained in contact with the panels until they died (2 h). Chlorfenapyr was also not repellent to bed bugs, but it caused no mortality during the 2-h test period. This study suggests that although pyrethroids were effective for controlling laboratory strain bed bugs, there is the potential for significant resistance in field strains. This study also determined that pyrethroid products were not repellent to bed bugs and would not cause bed bug aggregations to scatter or avoid treated surfaces.     

Assessment of Potential Sublethal Effects of Various Insecticides on Key Biological Traits of The Tobacco Whitefly,Bemisia tabaci

The tobacco whitefly Bemisia tabaci is one of the most devastating pests worldwide. Current management of B. tabaci relies upon the frequent applications of insecticides. In addition to direct mortality by typical acute toxicity (lethal effect), insecticides may also impair various key biological traits of the exposed insects through physiological and behavioral sublethal effects. Identifying and characterizing such effects could be crucial for understanding the global effects of insecticides on the pest and therefore for optimizing its management in the crops. We assessed the effects of sublethal and low-lethal concentrations of four widely used insecticides on the fecundity, honeydew excretion and feeding behavior of B. tabaci adults. The probing activity of the whiteflies feeding on treated cotton seedlings was recorded by an Electrical Penetration Graph (EPG). The results showed that imidacloprid and bifenthrin caused a reduction in phloem feeding even at sublethal concentrations. In addition, the honeydew excretions and fecundity levels of adults feeding on leaf discs treated with these concentrations were significantly lower than the untreated ones. While, sublethal concentrations of chlorpyrifos and carbosulfan did not affect feeding behavior, honeydew excretion and fecundity of the whitefly. We demonstrated an antifeedant effect of the imidacloprid and bifenthrin on B. tabaci, whereas behavioral changes in adults feeding on leaves treated with chlorpyrifos and carbosulfan were more likely caused by the direct effects of the insecticides on the insects'' nervous system itself. Our results show that aside from the lethal effect, the sublethal concentration of imidacloprid and bifenthrin impairs the phloem feeding, i.e. the most important feeding trait in a plant protection perspective. Indeed, this antifeedant property would give these insecticides potential to control insect pests indirectly. Therefore, the behavioral effects of sublethal concentrations of imidacloprid and bifenthrin may play an important role in the control of whitefly pests by increasing the toxicity persistence in treated crops.     

Evidence of Field-Evolved Resistance to Bifenthrin in Western Corn Rootworm (Diabrotica virgifera virgifera LeConte) Populations in Western Nebraska and Kansas

Pyrethroid insecticides have been used to control larvae or adults of the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, a key pest of field corn in the United States. In response to reports of reduced efficacy of pyrethroids in WCR management programs in southwestern areas of Nebraska and Kansas the present research was designed to establish a baseline of susceptibility to the pyrethroid insecticide, bifenthrin, using susceptible laboratory populations and to compare this baseline with susceptibility of field populations. Concentration-response bioassays were performed to estimate the baseline susceptibility. From the baseline data, a diagnostic concentration (LC₉₉) was determined and used to test adults of both laboratory and field populations. Larval susceptibility was also tested using both laboratory and field populations. Significant differences were recorded in adult and larval susceptibility among WCR field and laboratory populations. The highest LC₅₀ for WCR adults was observed in populations from Keith 2 and Chase Counties, NE, with LC₅₀s of 2.2 and 1.38 μg/vial, respectively, and Finney County 1, KS, with 1.43 μg/vial, as compared to a laboratory non-diapause population (0.24 μg/vial). For larvae, significant differences between WCR field and laboratory populations were also recorded. Significant differences in mortalities at the diagnostic bifenthrin concentration (LC₉₉) were observed among WCR adult populations with western Corn Belt populations exhibiting lower susceptibility to bifenthrin, especially in southwestern Nebraska and southwestern Kansas. This study provides evidence that resistance to bifenthrin is evolving in field populations that have been exposed for multiple years to pyrethroid insecticides. Implications to sustainable rootworm management are discussed.     

Relationship between toxicity of selected insecticides and expression of stress proteins (HSP, GRP) in cultured human cells: effects of commercial formulations versus pure active molecules

Three carbamate (formetanate, methomyl, pyrimicarb) and one pyrethroid (bifenthrin) insecticides were investigated both as pure chemicals and as commercial formulations in order to unveil possible toxic effects of additives and solvents present in the commercial formulations and to evaluate the cellular stress response as a defense mechanism. Toxic effects were evaluated on A549 cells, derived from a human lung carcinoma, by measuring (1) threshold concentrations leading to a decrease of the growth rate (LOEC), (2) sublethal concentrations (SC) which arrested growth without killing the cells, and (3) expression levels of several stress proteins, i.e., HSP27, HSP72/73, HSP90, GRP78, and GRP94. As compared to the pure active molecule, LOEC appeared at lower concentrations when using the commercial formulations, i.e., Dicarzol (formetanate), Lannate20 (methomyl) and Talstar or Kiros EV (bifenthrin). Propylene glycol and propylene glycol monomethyl ether, respectively, present in Talstar and kiros, do not account for the high toxicity of these commercial formulations and do not potentiate the toxicity of bifenthrin. Additive but not synergistic adverse effects were observed when cells are exposed to a mixture of 4 different commercial formulations. Our results show that the concentrations of active molecules recommended in flori-cultural general use or for spray preparations are much higher than SC concentrations, as determined on A549 pulmonary cells. GRP78 was up-regulated by all the insecticides, commercial preparations being more efficient to trigger the stress reaction. This suggests that insecticides and additives present in commercial formulations disrupt ER functions. Conversely, HSP72/73 was found to be down-regulated by all the insecticides. This seems to be related with a decrease of protein synthesis in the cytosol, as a result of the ER unfolded protein response. Indeed, tunicamycin, known to inhibit N-linked glycosylation in the ER, was found to induce a similar inverse correlation between GRP78 overexpression and HSP72/73 under-expression. Expression of GRP94 was found to be increased and HSP27 lowered by the highest concentrations of bifenthrin commercial formulations. Methomyl and Lannate20 only induced an under-expression of HSP90.     

Comparative susceptibility of western corn rootworm (Coleoptera: Chrysomelidae) adults to selected insecticides in Kansas

Susceptibility of adult populations of the western corn rootworm, Diabrotica virgifera virgifera LeConte, to several insecticides was evaluated in seven Kansas counties, including Dickinson, Ford, Finney, Pottawatomie, Republic, Riley, and Stevens, between 1996 and 2002. All populations surveyed were highly susceptible to methyl parathion with the largest difference in susceptibility of only three-fold based on 16 complete bioassays for the populations from six counties over a 5-yr period. Noticeable decreases in carbaryl susceptibility were found in populations collected from Republic County between 1997 and 2001 when the cucurbitacin-carbaryl-based bait SLAM was widely used as an areawide management approach for adult corn rootworm control. However, the lowered carbaryl susceptibility returned to previous levels 1 yr after the use of SLAM was halted in the managed (treated) cornfields. This change implies possible dispersal of insects into the relatively small managed area from surrounding untreated cornfields and / or some fitness cost associated with carbaryl resistance within the population. Relative susceptibility of western corn rootworm adults also was evaluated for seven commonly used insecticides, including bifenthrin, carbaryl, chlorpyrifos, cypermethrin, fipronil, malathion, and methyl parathion. They were tested with corn rootworm adults collected from a single cornfield. Methyl parathion and bifenthrin were highly toxic to corn rootworm adults, and cypermethrin, chlorpyrifos, carbaryl, and malathion were only slightly less toxic. Although fipronil was highly toxic to adult rootworms, its activity was much slower than that of other insecticides. Thus, bifenthrin and methyl parathion were among the most effective in killing corn rootworm adults.     

Comparative susceptibility of sweetpotato weevil (Coleoptera: Brentidae) to selected insecticides

The response of sweetpotato weevil, Cylas formicarius (F.) (Coleoptera: Brentidae), to insecticides used for its control was tested in laboratory bioassays. A glass vial bioassay technique was used to determine the susceptibility of two cohorts of sweetpotato weevil to selected insecticides. Vials were treated with methyl parathion, bifenthrin, cyfluthrin, carbaryl, and phosmet. Sweetpotato weevils demonstrated a mortality response to increasing concentrations of all insecticides tested, and our results indicated decreases in susceptibility of the Louisiana cohort of sweetpotato weevil compared with the Texas cohort for all insecticides tested. Methyl parathion was the most toxic chemical tested for both cohorts, followed by the pyrethroids, cyfluthrin and bifenthrin. Phosmet exhibited moderate toxicity compared with other chemicals tested, whereas sweetpotato weevils were least susceptible to carbaryl. Significant differences in lethal concentration (LC)50 and LC90 values for cyfluthrin and bifenthrin, the LC50 values for methyl parathion and phosmet, and the LC90 values for carbaryl were observed between the two cohorts. This study documents baseline toxicological data for five insecticides in two populations of sweetpotato weevil and demonstrates that susceptibility to all insecticides tested is lower for the Louisiana population compared with the Texas population.     

Establishment of baseline susceptibility data to various insecticides for Homalodisca coagulata (Homoptera: Cicadellidae) by comparative bioassay techniques

Homalodisca coagulata Say, adults from three locations in California were subjected to insecticide bioassays to establish baseline toxicity. Initially, two bioassay techniques, petri dish and leaf dip, were compared to determine the most useful method to establish baseline susceptibility data under laboratory and greenhouse conditions. Comparative dose-response data were determined by both techniques to endosulfan, dimethoate, cyfluthrin, and acetamiprid. Toxic values were similar to some insecticides with both techniques but not for all insecticides, revealing susceptibility differences among the three populations of H. coagulata. In subsequent tests, the petri dish technique was selected to establish baseline susceptibility data to various contact insecticides. A systemic uptake bioassay was adapted to estimate dose-mortality responses to a systemic insecticide, imidacloprid. A 2-yr comparison of toxicological responses showed all three populations of H. coagulata to be highly susceptible to 10 insecticides, including chlorpyrifos, dimethoate, endosulfan, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, acetamiprid, imidacloprid, and thiamethoxam. In general, two pyrethroids, bifenthrin and esfenvalerate, were the most toxic compounds, followed by two neonicotinoids, acetamiprid and imidacloprid. The LC50 values for all insecticides tested were lower than concentrations used as recommended field rates. Baseline data varied for the three geographically distinct H. coagulata populations with the petri dish technique. Adult H. coagulata collected from San Bernardino County were significantly more susceptible to select pyrethroids compared with adults from Riverside or Kern counties. Adults from San Bernardino County also were more sensitive to two neonicotinoids, acetamiprid and imidacloprid. The highest LC50 values were to endosulfan, which nonetheless proved highly toxic to H. coagulata from all three regions. In the majority of the tests, mortality increased over time resulting in increased susceptibility at 48 h compared with 24 h. These results indicate a wide selection of highly effective insecticides that could aid in managing H. coagulata populations in California.     

Development of neonicotinoid resistance in the cotton aphid Aphis gossypii (Hemiptera: Aphididae) in Japan

A neonicotinoid-resistant Aphis gossypii Glover population was first detected from cucumber and sweet pepper crops in Miyazaki Prefecture, Japan, in April 2012. In this study, we determined the insecticide susceptibility of five field-collected populations of A. gossypii to seven neonicotinoids. Insecticide susceptibility was determined by performing bioassays and using the seedling-treatment method. Insecticide susceptibility of a susceptible population of A. gossypii, originally collected from a cucumber field in 2008, was also determined. High mortality (96.4–100 %) was observed in the susceptible population for the seven insecticides. In contrast, the mortality rate of the five field-collected populations collected in 2012 was low for five of the seven neonicotinoid insecticides tested: imidacloprid (26.7–65.5 %), dinotefuran (0–27.3 %), clothianidin (20.0–35.7 %), thiamethoxam (7.1–42.3 %), and nitenpyram (6.7–32.1 %). Mortality was 86.2–100 % for acetamiprid and 90.2–100 % for thiacloprid. The resistance ratio in comparison with the susceptible population was the highest for clothianidin (687-fold), lowest for thiacloprid (17-fold), and ranged from 43- to 253-fold for the other five neonicotinoids. Thus, the frequency of insecticide use needs to be reduced and other insecticides need to be employed in order to prevent the development of resistance to these two insecticides in the future.     

Stink bug Agonoscelis spp. (Heteroptera: Pentatomidae) – An emerging threat for seed production in alfalfa crop (Medicago sativa L.) and their successful management

Fodder crops play an important role in sustainable agriculture as they provide feed for animals, which is ultimately converted to human food. Alfalfa is one of the most important fodder crops having high nutritive value for livestock. However, seed production of alfalfa crop is seriously affected by several factors and the highest reduction in seed yield is caused by stink bug infestation. The current study evaluated different insecticides to control stink bugs during 2016–17. The efficacy of ten insecticides, i.e., acephate, dimethoate, malathion, chlorpyriphos, bifenthrin, lambdacyhalothrin, deltamethrin, acetamiprid, imidacloprid and carbosulfan was tested on Agonoscelis spp. (Heteroptera Pentatomidae). The mortality of stink bug was recorded at one, three, five, seven, ten and fifteen days after insecticide application. Similarly, the population of pollinators was recorded before and one, three and five days after the application of insecticides. It was observed that acetamiprid (81.14%) and acephate (80.65%) caused the highest mortality of stink bug and proved most effective. Insecticides application decreased the pollinators’ population one day after spray; however, it was rehabilitated three days after insecticide application. Insecticide application increased seed yield from 28.05 kg/acre (during last four year without chemical control) to 116 kg/acre in 2016–17 (with chemical control). It is concluded that acetamiprid and acephate can be successfully used in integrated management program of increasing alfalfa seed production.     

Efficacy of mosquito nets treated with insecticide mixtures or mosaics against insecticide resistant Anopheles gambiae and Culex quinquefasciatus (Diptera: Culicidae) in Côte d'Ivoire

Only pyrethroid insecticides have so far been recommended for the treatment of mosquito nets for malaria control. Increasing resistance of malaria vectors to pyrethroids threatens to reduce the potency of this important method of vector control. Among the strategies proposed for resistance management is to use a pyrethroid and a non-pyrethroid insecticide in combination on the same mosquito net, either separately or as a mixture. Mixtures are particularly promising if there is potentiation between the two insecticides as this would make it possible to lower the dosage of each, as has been demonstrated under laboratory conditions for a mixture of bifenthrin (pyrethroid) and carbosulfan (carbamate). The effect of these types of treatment were compared in experimental huts on wild populations of Anopheles gambiae Giles and the nuisance mosquito Culex quinquefasciatus Say, both of which are multi-resistant. Four treatments were evaluated in experimental huts over six months: the recommended dosage of 50 mg m(-2) bifenthrin, 300 mg m(-2) carbosulfan, a mosaic of 300 mg m(-2) carbosulfan on the ceiling and 50 mg m(-2) bifenthrin on the sides, and a mixture of 6.25 mg m(-2) carbosulfan and 25 mg m(-2) bifenthrin. The mixture and mosaic treatments did not differ significantly in effectiveness from carbosulfan and bifenthrin alone against anophelines in terms of deterrency, induced exophily, blood feeding inhibition and overall mortality, but were more effective than in earlier tests with deltamethrin. These results are considered encouraging, as the combination of different classes of insecticides might be a potential tool for resistance management. The mixture might have an advantage in terms of lower cost and toxicity.     

Comparative efficacy of different pesticides against mango bark beetle Hypocryphalus mangiferae Stebbing (Coleoptera: Scolytidae)

Hypocryphalus mangiferae Stebbing is one of the most destructive insect pests of mango trees and is found to be associated with the transmission of causal organisms of mango sudden death disease. The present study was carried out to evaluate the toxicity of deltamethrin, bifenthrin, chlorpyrifos, emamectin benzoate, imidacloprid and spinosad in laboratory and field trials. Bioassay results showed that the toxicity of chlorpyrifos was significantly higher than deltamethrin but similar to bifenthrin. Deltamethrin and bifenthrin toxicity, however, increased significantly (P < 0.01) from day 1 to day 3. Spinosad was the least toxic compound while emamectin was the most toxic among new chemical insecticides tested, but its toxicity increased significantly from day 1 to day 5. Comparison of the efficacies of the insecticides using lethal times to produce 50% mortality (LT₅₀) and 90% mortality (LT₉₀) showed that the relative potencies of chlorpyrifos, emamectin, imidacloprid and spinosad were greater than bifenthrin and deltamethrin. The results of field trials showed the highest number of beetles emerged from the control twigs while significantly fewer beetles emerged from the twigs treated with bifenthrin (P < 0.05), which accounted for 12% for bifenthrin compared to that of the control. The present study demonstrated increased toxicities of systemic insecticides and chlorpyrifos compared to toxicities of deltamethrin and bifenthrin, suggesting these insecticides could be an alternative tool in a comprehensive H. mangiferae management program to eradicate the beetles from mango orchards.     

Biology and control of the raspberry crown borer (Lepidoptera: Sesiidae)

This study explored the biology of raspberry crown borer, Pennisetia marginata (Harris) (Lepidoptera: Sesiidae), in Arkansas and the optimum timing for insecticide and nematode applications. The duration of P. marginata's life cycle was observed to be 1 yr in Arkansas. Insecticide trials revealed that bifenthrin, chlorpyrifos, imidacloprid, metaflumizone, and metofluthrin efficacy were comparable with that of azinphosmethyl, the only labeled insecticide for P. marginata in brambles until 2005. Applications on 23 October 2003 for plots treated with bifenthrin, chlorpyrifos, and azinphosmethyl resulted in >88% reduction in larvae per crown. Applications on 3 November 2004 of metaflumizone, metofluthrin, and bifenthrin resulted in >89% reduction in larvae per crown. Applications on 7 April 2005 for metofluthrin, imidacloprid, bifenthrin, metaflumizone, and benzoylphenyl urea resulted in >64% reduction in the number of larvae per crown. Applications on 6 May 2004 did not reduce larval numbers. The optimum timing for treatments was found to be between October and early April, before the larvae tunneled into the crowns of plants. Applying bifenthrin with as little as 468 liters water/ha (50 gal/acre) was found to be as effective against larvae as higher volumes of spray. Nematode applications were less successful than insecticides. Nematode applications of Steinernemafeltiae, Steinernema carpocapsae, and Heterorhabditis bacteriophora reduced larvae counts per plant by 46, 53, and 33%, respectively.     

Baseline responses of adult Alphitobius diaperinus (Coleoptera: Tenebrionidae) to fenitrothion and susceptibility status of populations in Queensland and New South Wales, Australia

Traditionally in Australia, regular applications of insecticide to the floors and lower walls of broiler houses after cleanout periods have been used in an attempt to control lesser mealworm, Alphitobius diaperinus (Panzer). The Australian chicken meat industry has been concerned in recent years with the failure to control A. diaperinus in its broiler houses by using this method and with large beetle populations breaching farm biosecurity. Resistance to fenitrothion was suspected to be responsible for these recent control failures. In response, beetles from 13 poultry facilities were compared with an insecticide-susceptible reference population by using a topical application method. Generally, strong resistance to fenitrothion (up to 79 times that of the susceptible at the LC50) occurred in populations of A. diaperinus in long-established broiler growing areas of southeastern Queensland, where fenitrothion had been used continuously for up to 20 yr. In newly established broiler growing areas, where considerably less fenitrothion had been used (i.e., approximately 5 yr), much weaker or no resistance occurred. In addition, dose-mortality data generated for the susceptible reference beetle population over a range of fenitrothion concentrations showed that 0.15% fenitrothion at a LC(99.9) level could be used as a convenient topical dose concentration to discriminate between susceptible and resistant individuals. Using this method, the susceptibility of 27 field populations of A. diaperinus was determined. Of this total, 23 populations did not exhibit complete mortality against the discriminating concentration (mortality range 0-98.7%). Application of fenitrothion in Australian broiler houses for control of A. diaperinus has now ceased.     

Spatial and temporal variation in the control failure likelihood of the tomato leaf miner,Tuta absoluta

Insecticide resistance is frequently associated with field control failure, but such an assessment of its likelihood seldom occurs. This phenomenon is a potential cause of the control failure of the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae); therefore we surveyed insecticide resistance as the control failure likelihood for a duration of 7 years in 20 field populations of this species. The insecticide label rate was used as the discriminating concentration, and the minimum efficacy threshold required for insecticides in Brazil (i.e. 80% efficacy) was the targeted efficacy. The spatial and temporal variations of the control failure likelihood were also assessed, as was the potential influence of land topography for the area‐wide pattern observed. Most populations of T. absoluta were susceptible to abamectin, chlorfenapyr and spinosad and not to bifenthrin, triflumuron and teflubenzuron. The indoxacarb susceptibility varied in space and time. Spatial dependence was observed for abamectin and indoxacarb. The control failure likelihood of T. absoluta was higher for bifenthrin, triflumuron and teflubenzuron. A flat topography and the wind direction may favour the spread of the control failure likelihood and should be considered in designing pest management programs for T. absoluta.     

Insecticide susceptibility status in Mexican populations of Stegomyia aegypti (= Aedes aegypti): a nationwide assessment

In Mexico, mosquito vector‐borne diseases are of public health concern as a result of their impact on human morbidity and mortality. The use of insecticides against adult mosquitoes is one of the most common ways of controlling mosquito population densities. However, the use of these compounds has resulted in the development of insecticide resistance. The aim of this study was to estimate susceptibility to six pyrethroids, two carbamates and two organophosphates in Mexican populations of Stegomyia aegypti (Linnaeus, 1762) (= Aedes aegypti) (Diptera: Culicidae) mosquitoes. Bottle insecticide susceptibility tests, with 1 h exposure, were performed on adult mosquitoes from 75 localities across 28 states. At 30 min of exposure, the proportion of fallen mosquitoes was recorded. After 60 min of exposure, mosquitoes were recovered in non‐treated containers and mortality was determined at 24 h after the set‐up of the experiment. In general, the carbamate insecticides represented the most effective group in terms of the proportion of mosquitoes fallen at 30 min (72–100%) and 24‐h mortality (97–100%). High and widespread resistance to pyrethroids Types I and II and, to a lesser extent, to organophosphates was observed. Insecticide susceptibility among and within states was highly variable.     

Residual contact vial method for the rapid on-site detection of insecticide resistance in Thrips palmi

A residual contact vial plus water (RCVpW) bioassay method, in which water was supplemented to minimize control mortality, was established to monitor insecticide resistance in field populations of the melon thrips, Thrips palmi. In the RCVpW, median lethal doses (LD₅₀) of six insecticides commonly used in T. palmi control, were determined at 8 h post-treatment, using a susceptible RDA strain according to the RCVpW protocol. Diagnostic doses for on-site resistance monitoring of the six insecticides, which were determined as doses two-fold higher than required to achieve LD₉₀ in the RDA strain, were in the range of 0.299 to 164.3 μg^?1 cm². Insecticide resistance levels in five field populations of T. palmi were evaluated to test the applicability of RCVpW in monitoring the pest. Although the RDA strain exhibited 100% mortality to diagnostic doses, field populations showed a reduced mortality in response to all test insecticides, indicating different degrees of resistance. In particular, all test field populations exhibited a significantly low mortality in response to spinosad, suggesting a wide distribution of spinosad resistance. Synergistic bioassay revealed that cytochrome P450-mediated metabolic factor is involved in spinosad resistance in the Korean population. Interestingly, an apparently reduced mortality to emamectin benzoate and chlofenapyr was observed in some field populations, perhaps suggesting uneven distribution of resistance to these insecticides in field populations. Our study showed that the RCVpW protocol can be employed both as an on-site resistance monitoring method for major thrip species, and in the selection of appropriate insecticides for their control.     

Susceptibility of immature stages of Homalodisca coagulata (Hemiptera: Cicadellidae) to selected insecticides

Susceptibility of immatures of the glassy-winged sharpshooter, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), to 10 insecticides that included chlorpyrifos, dimethoate, endosulfan, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, acetamiprid, imidacloprid, and thiamethoxam was evaluated in the laboratory. All five instars were exposed to different doses of each foliar insecticide by the petri dish technique, whereas a systemic uptake method was used to assess the toxicity to imidacloprid and thiamethoxam. All test insecticides exhibited high toxicity to all immature stages of H. coagulata at concentrations below the field recommended rates of each insecticide. Although all five instars were susceptible to test insecticides, mortality was significantly higher in first instars than in the older immatures based on low LC50 values (ranging from 0.017 to 5.75 ng(AI)/ml) with susceptibility decreasing with each successive stage. Fifth instars were generally the least sensitive (LC50 values ranging from 0.325 to 216.63 ng (AI)/ml). These results show that mortality was directly related to age of the insect and suggest that chemical treatment at early stages is more effective than at late stages. Acetamiprid (neonicotinoid) and bifenthrin (pyrethroid) were the most toxic to all five instars, inducing most mortality within 24 h and showing lower LC50 values ranging from 0.017 to 0.686 ng/ml compared with other insecticides (LC50 values ranging from 0.191 to 216.63 ng(AI)/ml). Our data suggest that a diverse group of very effective insecticides are available to growers for controlling all stages of H. coagulata. Knowledge on toxicity of select insecticides to H. coagulata immatures may contribute to our understanding of resistance management in future for this pest by targeting specific life stages instead of the adult stage alone.     

Effect of insecticides used in corn, sorghum, and alfalfa on the predator Orius insidiosus (Hemiptera: Anthocoridae).

Orius insidoisus (Say) is an important predator in corn, sorghum, and alfalfa. Foliar insecticides commonly used on corn (permethrin, bifenthrin, and fipronil); sorghum (chlorpyrifos, carbofuran, dimethoate, and cyfluthrin); and both crops (A-cyhalothrin and ethyl parathion) were evaluated in 1998 and 1999 for their residual effects on O. insidiosus by caging adults on treated plants at several time intervals: at application (day 0) and 2, 3, and 6 d after application. In addition, imidacloprid, fipronil, and thiamethoxam used as seed treatments on corn and sorghum were tested for their effects on O. insidiosus by caging adults on plants in the presence and absence of greenbugs, Schizaphis graminum (Rondani). Finally, six of the same insecticides that also are used on alfalfa were evaluated in the field for their effects on O. insidiosus and other insects. On day 0, ethyl parathion. bifenthrin, and [lambda]-cyhalothrin on corn caused significantly higher mortality to O. insidiosus than permethrin and fipronil. Ethyl parathion and carbofuran on sorghum caused significantly higher mortality than chlorpyrifos, dimethoate, and A-cyhalothrin, which differed significantly from the control. Mortality with cyfluthrin did not differ significantly from that in the control. Insecticides had no significant effects on O. insidiosus 3 and 6 d after application in 1998 with the exception of permethrin on day 3. Similar patterns of mortality were observed in 1999 experiments. No significant differences in mortality of adults occurred with fipronil and thiamethoxam in the presence and absence of greenbugs. Imidachloprid caused significantly higher mortality to O. insidiosus adults than thiamethoxam or fipronil in some instances when greenbugs were not supplied as food. In alfalfa, the insecticides caused significant mortality to most of the insects evaluated. Ethyl parathion, permethrin, chlorpyrifos, and cyfluthrin caused significantly higher mortality to O. insidiosus than carbofuran and A-cyhalothrin, which differed significantly from the control in 1998. In 1999, all treatments significantly reduced O. insidiosus numbers and did not differ significantly from each other.     

Toxicity and repellency of some biorational insecticides toBemisia argentifolii on tomato plants

A mineral oil, an insecticidal soap, and a plant-derived surfactant were compared with a broad-spectrum pyrethroid for residual toxicity and repellency to silverleaf whitefly,Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) on tomatoes (Lycopersicum esculentum Miller, cv. Lanai) under greenhouse and laboratory conditions. The materials tested were: Sunspray oil (a mineral oil), M-Pede (an insecticidal soap),Nicotiana gossei extract (a sucrose ester surfactant), Garlic Barrier (repellency only), and the pyrethroid bifenthrin (Brigade 10WP), with water as a control. For toxicity studies, whiteflies were confined on leaves which had been dipped in solutions of 0.5×, 1× and 2× field rate concentrations. Insecticide residues were compared when the leaves were wet and dry. Adult mortalities were greatest with bifenthrin and Sunspray oil, followed by M-Pede,N. gossei extract and water. Mortality from dry residue of lower rates of bifenthrin and sunspray oil was greater than mortality from wet residues, whereas M-Pede lost all activity upon drying. Dual and multiple choice tests for repellency were carried out in the greenhouse or laboratory by spraying plants or individual leaves to runoff with 1 × field concentrations. Bifenthrin and Sunspray oil repelledB. argentifolii adults for up to 7 and 5 days, respectively, followed by M-Pede and extract ofN. gossei, whereas Garlic Barrier was not significantly different from the water control in all tests. Numbers of whitefly eggs were significantly reduced on bifenthrin and Sunspray oil-treated leaves, whereas egg numbers in other treatments were not different from water. Sunspray oil as a dip proved to be at least as effective as the synthetic pyrethroid for whitefly control. A multiple-choice leaf-wheel proved to be a useful device to quickly evaluate repellent effects of several different insecticides to whitefly.     

Digging behavior of Solenopsis invicta workers when exposed to contact insecticides

ABSTRACT Contact between ants and insecticides is a prerequisite for contact insecticides to be effective in the control of red imported fire ants, Solenopsis invicta Buren. Typically, passive contact occurs in the insecticide application process, but ants also may actively contact insecticides by digging in treated soil or walking on a treated soil surface. Laboratory experiments were conducted to determine whether fire ant workers would dig sand treated with contact insecticides in two different scenarios: (1) no-choice bioassays where insecticide-treated sand was the only available digging substrate, and (2) two-choice bioassays where nontoxicant sand was also available for digging. Eight insecticides that are currently registered in the United States for imported fire ant control were tested. They include acephate, bifenthrin, carbaryl, cyfluthrin, deltamethrin, gamma-cyhalothrin, permethrin, and pyrethrin. Workers dug the treated sand for every insecticide tested, even at concentrations up to 10 times of the lowest lethal concentration (LLC) which caused 100% mortality in a toxicity bioassay. However, generally, insecticides significantly reduced the digging effort, even at a concentration that did not cause any significant mortality in the toxicity bioassay.