Antifeeding effect of cypermethrin and permethrin at sub-lethal levels against Pieris brassicae larvae

An antifeeding (feeding deterrent) response by first- and fifth-instar larvae of Pieris brassicae was shown to be significant at sub-lethal levels of cypermethrin and permethrin, using leaf-discs treated with the pyrethroids by dipping. Permethrin was slightly more effective than cypermethrin both as an insecticide and as an antifeedant against fifth-instar larvae, but the reverse order of effectiveness was observed, with a marked difference in mortality, against newly-hatched larvae. When 1-day-old fifth-instar larvae were continuously given leaf discs treated with a solution of the pyrethroid (1 mg litre^?1), up to the time of pupation, both cypermethrin and permethrin induced a significant extension of the larval period, with a reduction in the maximum larval and pupal weights, as well as a reduction in the total leaf-area consumed. However, at higher levels of both pyrethroids, lowering the temperature induced some irritancy, as indicated by regurgitation and frequent uncoordinated wriggling movements of the fifth-instar larvae. The advantages of cypermethrin as a protectant and as an antifeedant over permethrin are discussed.     

Association between insecticide use and greenhouse whitefly (Trialeurodes vaporariorum westwood) resistance to insecticides in hawaii

Susceptibility to acephate, methomyl, and permethrin was determined with laboratory bioassays for adults of greenhouse whitefly, Trialeurodes vaporariorum Westwood, from 12 to 14 sites in Hawaii. Comparisons at LC₅₀ showed up to 42-fold resistance to acephate, 36-fold resistance to methomyl, and 8-fold resistance to permethrin. Higher levels of resistance to acephate and methomyl than to permethrin are consistent with greater use of organophosphates and carbamates than pyrethroids by growers. Insecticide use varied from 1 to 98 insecticide sprays per site per season. Significant positive associations between LC₅₀ for each insecticide and frequency of application of the same insecticide were found across sites. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.     

Adipokinetic hormone (Pyrap‐AKH) enhances the effect of a pyrethroid insecticide against the firebug Pyrrhocoris apterus

BACKGROUND: Adipokinetic hormones (AKHs) are insect neuropetides controlling stress situations including those elicited by insecticide treatment. The effect of Pyrap‐AKH on the mortality of the firebug Pyrrhocoris apterus (L.) treated with the insecticide permethrin (Ambush 25 EC) was studied. RESULTS: Coinjection of 50 ng permethrin with 80 pmol Pyrap‐AKH induced a significant 2.3‐fold increase in bug mortality compared with the insecticide alone. The results were confirmed by topical coapplication of both agents (400 ng and 80 pmol respectively). Injections of 50 and 100 ng permethrin elicited a significant increase in the AKH level in CNS and the haemolymph. The results indicate an involvement of AKH in stress response to permethrin. The enhanced effect of insecticide by AKH treatments probably results from the stimulatory role in bug metabolism: carbon dioxide production was increased 3.5‐ and 2.5‐fold respectively 1 and 3 h after permethrin treatment, and 4.3‐ and 3.4‐fold after the permethrin plus AKH cotreatment, compared with the control. CONCLUSION: The elevation of metabolism could intensify the permethrin action by its faster penetration into tissues and by stimulation of biochemically active cells, and could be a reason for enhanced action of permethrin after its cotreatment with Pyrap‐AKH. Copyright © 2009 Society of Chemical Industry     

Thermal behaviour and biological activity against Aedes aegypti (Diptera: Culicidae) of permethrin and pyriproxyfen in a smoke‐generating formulation

BACKGROUND: The most common ways to control dengue vector Aedes aegypti (L.) are larval source reduction in domestic habitats and ground application of small quantities of aerosol insecticide (ultralow volume). Nevertheless, these actions have been shown repeatedly to be ineffective in controlling Ae. aegypti populations. RESULTS: The efficacy of a new smoke‐generating formulation containing pyriproxyfen and permethrin was evaluated in the laboratory. Smoke‐generating tablets containing each insecticide individually or combined were prepared, and the recovery of the insecticides from the smoke was determined. Recovery values of over 90% were obtained for pyriproxyfen, and around 50% for permethrin. The biological efficacy of pyriproxyfen released in the smoke was evaluated in the laboratory, on late third‐instar or early fourth‐instar Ae. aegypti larvae, using different concentrations of pyriproxyfen and exposure times. Adult emergence inhibition (EI) values of 100% were obtained at 30 min, and a dose‐dependent effect was observed at 5 min. The effect of pyriproxyfen released in the smoke was due to direct contact with the larvicide in the water rather than by inhalation of the fumes. The efficacy of permethrin released in the fumes was also evaluated as knockdown effect (KT₅₀) on adults for a tablet containing permethrin alone or permethrin plus pyriproxyfen. There was no significant difference in KT₅₀ values obtained for permethrin (KT₅₀ = 19.9 min) and permethrin plus pyriproxyfen (KT₅₀ = 19.4 min). CONCLUSION: The excellent laboratory performance of this new formulation on immature stages and adults indicates that a smoke‐generating tablet containing pyriproxyfen and permethrin could be a new tool for controlling mosquitoes. Copyright © 2009 Society of Chemical Industry     

Evolutionary plasticity of monooxygenase-mediated resistance

The cytochrome P450 monooxygenases are an important metabolic system involved in the detoxification of xenobiotics, and are thus one of the major mechanisms by which insects evolve insecticide resistance. However, comparatively little is known about the evolutionary constraints of this insecticide resistance mechanism. We investigated the genetic basis of resistance in a strain of house fly (NG98) from Georgia, USA that had evolved 3700-fold resistance to the pyrethroid insecticide permethrin, and compared this to other permethrin resistant strains of house flies from the US and Japan. Resistance in NG98 was due to kdr on autosome 3 and monooxygenase-mediated resistance on autosomes 1, 2, and 5. These results indicate that the genes which evolve to produce monooxygenase-mediated resistance to permethrin are different between different populations, and that the P450 monooxygenases have some degree of plasticity in response to selection. Monooxygenase-mediated resistance appears to evolve using different P450s, and possibly different regulatory signals controlling P450 expression, even in strains selected with the same insecticide.     

Effects of residues of fenvalerate and permethrin on the feeding behaviour of Tetranychus urticae (Koch)

The effects of synthetic pyrethroids on the feeding behaviour of the two-spotted spider mite Tetranychus urticae (Koch) were studied using a modified leaf disc technique. Four different concentrations of the pyrethroids fenvalerate and permethrin and of the organophosphorous insecticide phosmet were sprayed on to Henderson lima bean plants in the laboratory. A water spray was used as a control. Leaf discs were taken from each treatment, including the control, at 2h, 1, 2, 4, 7, 11 and 14 days after treatment. One mite was placed on each disc, allowed to acclimatise and then observed for 1 h. Experiments were conducted under laboratory light at 25 (±1.5)°C and 30 (±2)% r.h. Mites on untreated and phosmet-treated discs spent an average 70–95% of the time feeding; mite behaviour appeared to be unaffected by phosmet. In contrast, mites often spent only 5–40% of the time feeding on discs treated with fenvalerate or with the higher rates of permethrin. In response to pyrethroid residues mites exhibited hyperactivity, longer search periods and reduced feeding, reduced oviposition and a preference for areas with lower residues. These changes in mite behaviour may partially explain mite outbreaks in the field on apple trees following treatment with pyrethroids.     

The use of [3H] permethrin to investigate the mechanisms underlying its differential toxicity to adult and larval stages of the sheen blowfly Lucilia sericata

Observations suggest that more than one mechanism is responsible for the increased tolerance to permethrin in the larval stage of Lucilia sericata. While the penetration rate of permethrin was much reduced in larvae, they remained more tolerant than adults when this compound was injected. Following the injection of sublethal amounts of [³H]-(1 RS)-trans-permethrin, a substantial proportion of the dose was accumulated and retained in the larval fat body. In adults, less permethrin was absorbed and retained in the tissues. However, compared to the larvae, detoxication was faster, haemoplasm levels were lower, and substantially more breakdown products were excreted. The injection of sublethal amounts of permethrin into the larva led to severe disruption of sensory function. These findings suggest that an important difference may exist between adults and larvae in either the sensitivity of vital sites within the nervous system, or in the sequence of events which follow nervous system disruption and lead to death.     

Efficacy of insecticide mixtures against larvae of Culex quinquefasciatus (Say) (Diptera: Culicidae) resistant to pyrethroids and carbamates

The efficacy of insecticide mixtures of permethrin (pyrethroid) and propoxur (carbamate) was tested by larval bioassays on two strains of Culex quinquefasciatus (Say), one resistant to pyrethroids and the other resistant to carbamates. The method consisted in combining one insecticide at the highest concentration causing no mortality (LC0) with increasing concentrations of the second one. The concentration-mortality regression lines were determined for permethrin and propoxur alone and in combination, and synergism ratios (SR) were calculated in order to determine the magnitude of an increase or decrease in efficacy with use of the mixtures. With the pyrethroid-resistant strain (BK-PER), the results showed that propoxur at LC0 significantly enhanced the insecticidal activity of permethrin (SR50 = 1.54), especially on the upper range of the concentration-mortality regression. Conversely, when permethrin at LC0 was tested with propoxur against the carbamate resistant strain (R-LAB), an antagonistic effect was observed (SR50 = 0.67). With the BK-PER strain, an increased oxidative detoxification (MFO) appeared to be the main mechanism responsible for the synergistic interaction. Nevertheless, antagonism in the R-LAB strain is probably due to a physiological perturbation implying different target sites for pyrethroid (ie sodium channel) and carbamate insecticides [ie acetylcholinesterase (EC 3.3.3.7) and choline acetyltransferase (EC 2.3.1.6)].     

Susceptibility of standard clones and European field populations of the green peach aphid, Myzus persicae, and the cotton aphid, Aphis gossypii (Hemiptera: Aphididae), to the novel anthranilic diamide insecticide cyantraniliprole

BACKGROUND: Parthenogenetic clones of the green peach aphid, Myzus persicae (Sulzer), and the cotton aphid, Aphis gossypii Glover, were tested with the anthranilic diamide insecticide cyantraniliprole (i.e. DuPont^? Cyazypyr^?) in systemic‐uptake bioassays to investigate potential for cross‐resistance conferred by mechanisms of insecticide resistance to organophosphates, carbamates and pyrethroids and, in the case of M. persicae, reduced sensitivity to neonicotinoids. These data were compared with the response of field samples of M. persicae and A. gossypii collected from around Europe. RESULTS: Cyantraniliprole was not cross‐resisted by any of the known insecticide resistance mechanisms present in M. persicae or A. gossypii. The compound was equally active against resistant and susceptible aphid strains. The responses of the M. persicae field samples were very consistent with a maximum response ratio of 2.9 compared with a standard laboratory clone. The responses of the A. gossypii field samples were more variable, although a majority of the responses were not statistically different. CONCLUSION: Cyantraniliprole is currently the only anthranilic diamide (IRAC MoA 28) insecticide targeting aphid species such as M. persicae and A. gossypii. There is no evidence to suggest that the performance of this compound is affected by commonly occurring mechanisms that confer resistance to other insecticide chemistries. Cyantraniliprole is therefore a valuable tool for managing insecticide resistance in these globally important pests. Copyright © 2011 Society of Chemical Industry     

Cross‐resistance between azinphos‐methyl and acetamiprid in populations of codling moth,Cydia pomonella (L.) (Lepidoptera: Tortricidae), from Washington State

BACKGROUND: Codling moth, Cydia pomonella (L.), has been intensely managed with the organophosphate insecticide azinphos‐methyl for 50 years, and populations have developed resistance. New management programs have been developed and implemented that rely more heavily on other classes of insecticides. A prerequisite for developing effective resistance management strategies for these compounds is to establish their current levels of effectiveness. Adult and neonate larval assays were conducted to assess the response of field‐collected codling moth populations from apple in Washington State. RESULTS: Male codling moth populations exhibited a range of responses to a discriminating concentration of azinphos‐methyl in a survey of 20 populations. Populations from certified organic orchards were more susceptible than those from conventional orchards. Mean fecundity was inversely related to azinphos‐methyl tolerance. Male responses to azinphos‐methyl and acetamiprid varied significantly among populations and were correlated. The residual effectiveness of field applications of both insecticides varied significantly against neonate larvae. Neonate bioassays with insecticide‐dipped fruit found significant differences among populations with azinphos‐methyl, acetamiprid, methoxyfenozide and spinosad, but not with esfenvalerate. CONCLUSION: These results support a concern that alternation of insecticides with different modes of action may not be a sufficient strategy to avoid the evolution of broad‐spectrum insecticide resistance by codling moth. Published 2010 by John Wiley & Sons, Ltd.     

Investigation of a permethrin-induced antifeedant effect in Drosophila melanogaster: An ethological approach

A permethrin-induced antifeedant effect was demonstrated in Drosophila melanogaster topically treated with a dose of 1.25 ng per fly (LD₅₀ and LD₁₀ were 18.5 and 7.4 ng of permethrin per fly, respectively). The reduction in food consumption in treated flies was due to a decrease in the frequency of feeding and not to the duration of individual meals. These results suggested that the sublethal effect occurred before the process of ingestion. Furthermore, a time-sampling study of individual flies, 30 min after treatment, revealed that the relative frequency of the components of general behaviour were altered. Specifically, locomotory behaviour and inactivity were significantly decreased in contrast to preening, which increased. Continuous observation for 30 min revealed that whilst the length of preening bouts was unaltered, their frequency of occurrence was significantly increased in permethrin-treated flies. The length of bouts of locomotory activity was significantly reduced in treated individuals, but the frequency was increased. The length of rest periods was reduced in treated flies, but no influence of the insecticide could be detected on their bout frequency. Sequential analysis of the transition frequencies of the behavioural components suggested that an underlying disorganisation of general behaviour resulted from the insecticide treatment. Further analysis, of the behaviour of those flies that had fed, indicated that the probability of tasting leading to feeding was decreased by permethrin. The increase in preening behaviour was thought to cause the reduction in locomotor activity, that ultimately resulted in the reduction in feeding. This is discussed in relation to the physiological basis of pyrethroid action and a subsequent irritation response to low doses.     

The persistence of insecticide spray deposits on woven polypropylene and jute sacking

In a trial, simulating the spray treatment of bags, the persistence and biological activity of insecticide spray deposits on jute and woven polypropylene sheets have been compared; in addition, the build-up of residues in thin layers of maize under the sprayed sheets has been measured. The insecticides were found to have a much shorter persistence on polypropylene than on jute and this was coupled with higher residues on the grain. However, the deposits on polypropylene retained equal or greater activity against Sitophilus zeamais Motsch. and Tribolium castaneum (Herbst) than the deposits on jute, despite the loss of surface deposit. Wettable powder formulations had a slightly greater surface persistence than emulsifiable concentrates and resulted in smaller residues in the grain. There would seem to be more usefulness in using insecticide sprays on woven polypropylene than on jute bags, and a wettable powder formulation of a non-volatile insecticide of low mammalian toxicity would be the best choice. Of the insecticides tested, the pyrethroid permethrin (cis: trans ratio= 25:75) was the most effective and gave the least residue in the grain.     

Laboratory evaluation of fipronil,a phenylpyrazole insecticide,against adult Anopheles (Diptera: Culicidae) and investigation of its possible cross‐resistance with dieldrin in Anopheles stephensi

Adult mosquitoes from two strains of Anopheles gambiae and from three strains of Anopheles stephensi were exposed to 0.25% fipronil‐treated papers in WHO test kits or to 500 mg fipronil m⁻² impregnated mosquito netting in bioassay spheres. For comparison, tests were also carried out with the pyrethroid permethrin, using the same methods and doses, and on papers treated with 0.4 and 4% of the cyclodiene insecticide dieldrin. Compared with the same doses of permethrin, fipronil showed less and delayed activity. Two of the An stephensi strains were resistant to fipronil and dieldrin. To investigate whether this was due to a resistance mechanism in the An stephensi strains acting against both insecticides, the most fipronil‐ and dieldrin‐tolerant strain was further selected in two separate lines with one of the insecticides, followed by tests with the insecticide that the line had not been selected with. This indicated a concomitant rise of resistance to dieldrin in the fipronil‐selected line and vice versa. Repeated back‐crossing of the two lines with a susceptible strain and re‐selection with either dieldrin or fipronil gave evidence for the involvement of a single resistance mechanism to both insecticides. Permethrin resistance in both lines declined with selection for dieldrin or fipronil and confirms the absence of cross‐resistance between fipronil and pyrethroids. © 2001 Society of Chemical Industry     

Response of citrus peelminer Marmara gulosa Guillén and Davis (Lepidoptera: Gracillariidae) stages to various insecticides

BACKGROUND: Egg and larval stages of citrus peelminer Marmara gulosa Guillén and Davis infesting zucchini squash Cucurbita pepo L. var ‘Revenue’ were exposed in the laboratory to a wide range of insecticide classes used in California citrus (organophosphate, carbamate, pyrethroid, neonicotinoid, insect growth regulator, fermentation products and sulfur) to determine peelminer response with and without a non‐ionic adjuvant or oil. RESULTS: All of the insecticides tested except sulfur reduced egg hatch and mine initiation. When the larval stage was treated, only buprofezin failed to reduce larval and pupal development. Cyfluthrin and spinosad, with the addition of adjuvant or oil, and abamectin combined with oil allowed no survivors at 7 days after treatment (DAT). The slower‐acting insect growth regulators pyriproxyfen and diflubenzuron applied in combination with adjuvant or oil allowed no survival of peelminer 21 DAT. A field trial showed 62.6–68.5% reduction in mined citrus fruit after two applications of diflubenzuron and no significant improvement of control with the addition of cyfluthrin. CONCLUSION: Bioassays indicate that M. gulosa is relatively susceptible to a wide range of insecticide classes in the laboratory. Lack of efficacy experienced in field trials would then be due to characteristics of the fruit or canopy that limit coverage, rather than to the effectiveness of the insecticides. Copyright © 2008 Society of Chemical Industry     

Insecticide resistance patterns among colorado potato beetle,leptinotarsa decemlineata (Say) (Coleoptera: chrysomelidae), populations in north carolina

A residual bioassay was used to determine insecticide susceptibility in populations of Colarado potato beetle, Leptinotarsa decemlineata (Say), in eastern North Carolina. Mean bioassay mortalities were subjected to correlation analysis to assess patterns of resistance among tested insecticides. Within insecticide classes, cross-resistance patterns were observed between carbaryl and carbofuran (carbamates), fenvalerate and permethrin (pyrethroids), and among azinphosmethyl, methamidophos, and phosmet (organophosphates). Significant associations between insecticides from different insecticide classes were concluded to be due to multiple resistance. Knowledge of multiple and cross-resistance patterns are discussed in relation to the bioassay as a tool for monitoring insecticide resistance.     

Foraging mode: a factor affecting the susceptibility of spiders (Araneae) to insecticide applications

Field experiments have revealed that some species of spiders are more sensitive to insecticides than others. Among many factors influencing their susceptibility, foraging mode seems to play an important role. Aspects of foraging mode that appear to be relevant are whether the spider is diurnal or nocturnal, a hunter or a web-maker. Six spider species, Araniella opisthographa, Clubiona neglecta, Dictyna uncinata, Pardosa agrestis, Philodromus cespitum and Theridion impressum were used in the study. P agrestis and P cespitum are diurnal hunters that may come into direct contact with insecticide. C neglecta is nocturnal and so is exposed to residues only. The remaining three species are web-makers building webs that vary in the extent to which they can protect the spider from direct spray. The effect of sprays was tested under laboratory conditions (Potter tower) with three commercial insecticides, an insect growth regulator (hexaflumuron), a selective organophosphorus (phosalone) and a non-selective pyrethroid insecticide (permethrin) using a four-day exposure period. Data were analysed using bootstrap method and randomization tests. The results obtained showed that hunting spiders were more susceptible to the insecticides tested than web-makers (in their webs). Diurnal hunting spiders (Philodromus and Pardosa) were severely affected only by permethrin. A high mortality was observed for the nocturnal hunter, Clubiona, after application of phosalone and permethrin. This species appears to be very sensitive to residues of both insecticides. Comparing the effect on web-making spiders, with and without webs, it was observed that the sparse orb-web of Araniella did not protect its owner at all, but the dense cribellate and frame-webs of Dictyna and Theridion, respectively, reduced the mortality caused by permethrin significantly in comparison with specimens without webs. Of other factors studied, posture (normal and upside-down position) did not influence the susceptibility. Mortality increased slightly with body size after permethrin application. © 1999 Society of Chemical Industry     

Evaluation of food sprays and relay strip crops for enhancing biological control of bollworms and cotton aphids in cotton

Studies were conducted at the Texas Agricultural Experiment Station research farms located at Munday (1996 test) and Chillicothe (1997 test) to evaluate relay strip crops in combination with a food spray to enhance biological control of bollworms, Helicoverpa zea (Boddie), and cotton aphids, Aphis gossypii Glover, in cotton. The relay crops included fall plantings of hairy vetch, Vicia villosa Roth, and canola, Brassica napus L., and a spring planting of grain sorghum, Sorghum bicolor L. Cotton, Gossypium hirsutum L., was planted between the relay crops or was isolated from the relay crops. Treatments within the two cotton systems included an untreated check plot, a plot sprayed with sugar+yeast (food spray) during summer to attract and hold predator insects, a plot sprayed with biological ('soft') insecticides for bollworm and cotton aphid control (Bacillus thuringiensis and pymetrozine, respectively), and a plot sprayed with harsh insecticides for bollworm and cotton aphid control (zeta cypermethrin and dicrotophos or profonofos, respectively). A split-plot experimental design, with three replications, was used where whole plots included relay and isolated cotton systems and subplots were the four food/chemical treatments. Predator numbers were monitored with a vacuum sampler once a week in relay crops and cotton. Bollworms and cotton aphids were monitored visually once a week in cotton during July and August. Total predator numbers were higher in cotton adjacent to relay crops in 1996, but not in 1997. The food spray did not enhance attraction and retention of predators either year. Bollworm larval numbers were significantly higher in relay cotton, food spray plots in 1996. Bollworm larval numbers were similar in relay and isolated cotton, and larval numbers were significantly reduced only in the plot where zeta cypermethrin (harsh insecticide plot) was used. In 1996, cotton aphid numbers in the relay cotton system were significantly higher in the untreated check plots in relation to numbers in the food spray, soft insecticide, and harsh insecticide plots, which were statistically similar. In the isolated cotton system, aphid numbers were highest in untreated plots, intermediate in food spray and soft insecticide plots, and lowest in the harsh insecticide plots. Aphid numbers increased more rapidly in the harsh insecticide plots that had been treated previously for bollworm control. The food spray and pymetrozine treatments reduced cotton aphids more effectively in the relay cropping system than in the isolated cotton system. Bollworms and cotton aphids did not reach pest status in 1997. The combination of a relay cropping system with a food spray did not enhance predator numbers and did not aid in retention of predators in cotton during August. Sucrose in the food spray attracted high numbers of bollworms in 1996.     

The Experimental Application of Insecticides from a Helicopter for the Control of Riverine Populations of Glossina tachinoides in West Africa. IV. Evaluation of Insecticides Applied as Aerosols

Abstract

The effects of aerosol dosages of different categories of insecticide were tested against Glossina tachinoides when applied by helicopter to riverine forest habitats of the River Komoe, Upper Volta, West Africa. The method of application, droplet characteristics of the aerosols and meteorological conditions are described in accompanying papers. Comparative trials based on field dosages calculated initially from dosage mortality curves obtained from topical application studies in the laboratory were carried out. Endosulfan applied at 5.4 g a.i./ha and 9.0 g a.i./ha reduced G. tachinoides populations (determined by Challier/Laveissière traps) by more than 90% in all age and sex categories and evidence is presented which indicates a residual effect at the higher of these dosages. Good results were also obtained with the synthetic pyrethroid decamethrin at a dosage of 0.36 g a.i./ha; another synthetic pyrethroid, permethrin, gave promising results at a dosage of 1.9 g a.i./ha. At the higher dosage of 4.3 g a.i./ha disappointing results were obtained, which were considered to be more attributable to a weakness in the application technique under challenging field conditions, than to a limitation of the insecticide. The organophosphate compounds tested, fenthion, azamethiphos and tetrachlorvinphos although known from laboratory tests to be appreciably toxic to G. tachinoides, performed poorly under field conditions. This was thought to be due to the formulations employed and the authors feel that further small-scale field testing of different formulations of these compounds is warranted. The compounds considered most worthy of larger scale field evaluation were endosulfan and permethrin. Although decamethrin was also very toxic to G. tachinoides it was considered inadvisable to field test this compound on a larger scale, until more information was available on its impact on aquatic food chains. The trials demonstrated that it is not always possible to extrapolate from laboratory-obtained comparative dosage/mortality data (in ng/fly) the field dosages of insecticides (in g a.i./ha) required to produce a certain level of mortality in target populations of G. tachinoides.     

Responses of striped stem borer,Chilo suppressalis (Lepidoptera: Pyralidae), from Taiwan to a range of insecticides

BACKGROUND: Information on the insecticide susceptibility of striped stem borer, Chilo suppressalis (Walker), is essential for an effective pest management programme. An early detection of resistance development can prompt the modification of current control methods and increase the lifespan of insecticides through the rotation of chemicals with different modes of action. In this study, the susceptibility of this pest in Taiwan to four classes of insecticides has been examined. RESULTS: Over 1000‐fold resistance to carbofuran was detected in C. suppressalis collected from Chiayi and Changhua prefectures, with estimated LC₅₀ values of > 3 mg cm^?2. In addition, 61‐fold resistance to cartap was found in the Chiayi population. On the other hand, all tested populations of rice stem borer were still relatively susceptible to chlorpyrifos, fipronil and permethrin, with LC₅₀ values ranging from 30 to 553 ng cm^?2. Chilo suppressalis populations collected from the central parts of Taiwan have a higher degree of resistance to the tested insecticides than those from northern areas. CONCLUSION: The occurrence of high resistance to carbofuran in the Chiayi and Changhua areas suggests that this compound should be replaced with chemicals having a different mode of action, such as chlorpyrifos, fipronil and permethrin, to which low cross‐resistance has been detected. Copyright © 2010 Society of Chemical Industry