Surface contact toxicity and synergism of several insecticides against different stages of the tropical bed bug, Cimex hemipterus (Hemiptera: Cimicidae)

BACKGROUND: Five formulated insecticides (lambda‐cyhalothrin at 10 mg m^?2, bifenthrin at 50 mg m^?2, fipronil at 10 mg m^?2, fenitrothion at 50 mg m^?2, imidacloprid at 5 mg m^?2) and one active ingredient (DDT at 500 mg m^?2) were evaluated using a surface contact method against early and late instars and adults of two strains of the tropical bed bug, Cimex hemipterus (F.). Synergism of lambda‐cyhalothrin and fipronil using piperonyl butoxide (PBO) was also assessed. RESULTS: The order of susceptibility of different stages of bed bugs was as follows: early stage ? lambda‐cyhalothrin > bifenthrin = imidacloprid > fipronil > fenitrothion > DDT; late stage—lambda‐cyhalothrin > bifenthrin > fenitrothion > imidacloprid > fipronil > DDT; adult—lambda‐cyhalothrin > imidacloprid > bifenthrin > fenitrothion > fipronil > DDT. The late instars exhibited significantly higher LT₅₀ among the life stages. The addition of PBO to fipronil increased the susceptibility of the insects. CONCLUSIONS: Lambda‐cyhalothrin, bifenthrin, fenitrothion and fipronil at the recommended application rates were effective against C. hemipterus. Although imidacloprid demonstrated good initial response against C. hemipterus, the insects showed substantial recovery 72 h post‐treatment. The late instars (fourth and fifth instars) should be used as the model for toxicological evaluation. Copyright © 2011 Society of Chemical Industry     

Comparative acute toxicity of neonicotinoid and pyrethroid insecticides to non‐target crayfish (Procambarus clarkii) associated with rice–crayfish crop rotations

BACKGROUND: Most insecticides used to control rice water weevil (Lissorhoptrus oryzophilus Kuscel) infestations are pyrethroids. However, pyrethroids are highly toxic to non‐target crayfish associated with rice–crayfish crop rotations. One solution to the near‐exclusive reliance on pyrethroids in a rice–crayfish pest management program is to incorporate neonicotinoid insecticides, which are insect specific and effective against weevils but not extremely toxic to crayfish. This study aimed to take the first step to assess neonicotinoids as alternatives to pyrethroids in rice–crayfish crop rotations by measuring the acute toxicities of three candidate neonicotinoid insecticides, clothianidin, dinotefuran and thiamethoxam, to juvenile Procambarus clarkii (Girard) crayfish and comparing them with the acute toxicities of two currently used pyrethroid insecticides, lambda‐cyhalothrin and etofenprox. RESULTS: Neonicotinoid insecticides are at least 2–3 orders of magnitude less acutely toxic (96 h LC₅₀) than pyrethroids to juvenile Procambarid crayfish: lambda‐cyhalothrin (0.16 µg AI L^?1) = etofenprox (0.29 µg AI L^?1) ? clothianidin (59 µg AI L^?1) > thiamethoxam (967 µg AI L^?1) > dinotefuran (2032 µg AI L^?1). CONCLUSION: Neonicotinoid insecticides appear to be much less hazardous alternatives to pyrethroids in rice–crayfish crop rotations. Further field‐level neonicotinoid acute and chronic toxicity testing with crayfish is needed. Copyright © 2009 Society of Chemical Industry     

Organophosphorothioates and synergised synthetic pyrethroids as grain protectants on bulk wheat

Organophosphorothioates and synergised synthetic pyrethroids were used in duplicate field trials carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays using malathion-resistant strains of insects were carried out on samples of treated grain at intervals over 9 months. These established that all treatments were generally effective. Deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ fenvalerate (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ phenothrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) and pirimiphos-methyl (4 mg kg^?1)+ permethrin (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) controlled common field strains of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.). Against a highly resistant strain of S. oryzae, deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) was superior to the remaining treatments. All treatment combinations completely prevented progeny production in Tribolium castaneum (Herbst), T. confusum Jacquelin du Val and in Ephestia cautella (Walker). Residues of deltamethrin, fenvalerate, permethrin and phenothrin were determined and shown to be highly persistent on stored wheat. During milling, residues accumulated in the bran fractions and were reduced in white flour. They were not significantly reduced during baking.     

Combinations of pirimiphos-methyl and carbaryl for stored grain protection

In laboratory experiments, whole wheat was treated with pirimiphos-methyl or carbaryl or combinations of these two insecticides; the treated grain was then adjusted to a 12% moisture content and stored at 25°C for bioassay at various intervals over a period of 39 weeks. Pirimiphos-methyl at 5.1 mg kg^?1 effectively controlled Sitophilus granarius (L.) and Tribolium confusum Jacquelin du Val but was ineffective against Rhyzopertha dominica (F.) CRD 118, a strain showing malathion resistance. Conversely, carbaryl at 6.5 mg kg^?1 (but not at 3.1 mg kg^?1) was effective against R. dominica, but ineffective against the other two species. A combination of pirimiphosmethyl + carbaryl, at 1.8 + 5.1 mg kg^?1, controlled S. granarius and R dominica but not T. confusum, whilst a 4.2 + 3.4 mg kg^?1 combination was relatively more effective against T. confusum but less so against R. dominica. In a separate experiment, whole wheat was treated with carbaryl at 2.5, 5.0 and 7.5 mg kg^?1 (nominal rates). Samples were stored and, at various times after the treatments, were bioassayed with R. dominica CRD 2, at 20, 25, 30 and 35°C. The results were comparable with those for the CRD 118 strain, but efficacy was reduced at higher temperatures. The combination of pirimiphos-methyl at 4–5 mg kg^?1 and carbaryl at 5–6 mg kg^?1 is suggested as a potentially useful grain protectant where R. dominica is a problem and long term storage is required. These results are discussed in relation to the protection of stored grain in Australia.     

A laboratory evaluation of the effectiveness of diflubenzuron against Dermestes maculatus De Geer and other storage insect pests

The chitin synthesis inhibitor diflubenzuron, applied as a wettable powder spray to woven polypropylene at 100–500 mg m^?2, was effective against Dermestes maculatus De Geer for at least 12 weeks. D. maculatus was unable to develop on ox hide dipped in a suspension of diflubenzuron (125 mg litre^?1), or on fishmeal dusted at 1–10 mg of active ingredient kg^?1. Diflubenzuron prevented the development of infestations of Callosobruchus maculatus (L.) on peas and of Acanthoscelides obtectus (Say) on beans dusted at 1–5 mg kg^?1. The compound was also very effective against early instar larvae of Trogoderma granarium Everts on wheat. The persistence and activity of diflubenzuron at low dosage rates against D. maculatus appear to justify larger scale trials.     

双委夜蛾幼虫对不同类别杀虫剂的敏感性及中毒症状

为筛选防治农业新发害虫双委夜蛾Athetis dissimilis（Hampson）的有效药剂,采用浸叶法测定了其不同龄期幼虫对8类18种常用杀虫剂的敏感性,并观察了幼虫对不同药剂的中毒症状。结果表明:3~6龄双委夜蛾幼虫对辛硫磷、联苯菊酯、高效氯氟氰菊酯、溴氰菊酯、甲氨基阿维菌素苯甲酸盐、氯虫苯甲酰胺和溴氰虫酰胺的敏感性较高,LC50值为0.138 1~27.40 mg/L;3龄及4龄幼虫对毒死蜱、高效氯氰菊酯、氟啶脲、茚虫威和虫螨腈敏感性较高,LC50值小于22.63 mg/L,而5龄和6龄幼虫对上述药剂的敏感性均有所降低,LC50值大于38.13 mg/L;各龄期幼虫对甲基嘧啶磷、灭幼脲及新烟碱类杀虫剂的敏感性均较低,LC50值大于40.83 mg/L。双委夜蛾幼虫对不同类别杀虫剂的中毒症状存在差异,其中,经有机磷类、新烟碱类、吡咯类及齅二嗪类杀虫剂处理后,幼虫表现为体表干燥、体壁皱缩;而经拟除虫菊酯类杀虫剂处理后幼虫表现为体壁柔软、充满体液。就生物活性测定结果而言,推荐溴氰虫酰胺、氯虫苯甲酰胺、辛硫磷、联苯菊酯、高效氯氟氰菊酯、溴氰菊酯及甲氨基阿维菌素苯甲酸盐等药剂可用于双委夜蛾的应急防治。     

Resistance of Pakistani field populations of spotted bollworm Earias vittella (Lepidoptera: Noctuidae) to pyrethroid,organophosphorus and new chemical insecticides

BACKGROUND: The spotted bollworm Earias vittella (Fab.) is a serious pest of cotton and okra in Pakistan. Owing to persistent use of insecticides, this pest has developed resistance, especially to pyrethroids. The present studies aimed at determining the extent of resistance to pyrethroid, organophosphorus and new chemical insecticides in Pakistani populations of E. vittella. RESULTS: Field populations of E. vittella were monitored at Multan, Pakistan, from 1999 to 2007 for their resistance against six pyrethroid, four organophosphorus and six new chemical insecticides using a leaf‐dip bioassay. Of the pyrethroids, resistance was generally low to zeta‐cypermethrin and moderate to high or very high to cypermethrin, deltamethrin, esfenvalerate, bifenthrin and lambda‐cyhalothrin. Resistance to organophosphates chlorpyrifos, profenofos, triazophos and phoxim was recorded at very low to low levels. Among new chemicals, E. vittella had no or a very low resistance to spinosad, emamectin benzoate and methoxyfenozide, a very low to low resistance to abamectin, a very low to moderate resistance to indoxacarb and a moderate resistance to chlorfenapyr. CONCLUSION: The results indicate a lack of cross‐resistance between pyrethroid and organophosphorus insecticides in E. vittella. Rotation of insecticides showing no, very low or low resistance, but belonging to different insecticide classes with unrelated modes of action, may prevent or mitigate insecticide resistance in E. vittella. Copyright © 2009 Society of Chemical Industry     

A new resistance to pyrethroids in tribolium castaneum (herbst)

The characteristics of a new high-level, field-derived resistance to pyrethroids in Tribolium castaneum (Herbst) were investigated using impregnated-paper and treated-grain assays. Piperonyl butoxide almost completely suppressed the resistance, suggesting that the major resistance mechanism was microsomal oxidation. Resistance extended to all pyrethroids tested and to carbaryl but not to organophosphorus insecticides or to methoprene. Resistance was strongest against α—CN phenoxybenzyl cyclopropanecarboxylate pyrethroids and was correlated with structural modifications of the pyrethroid molecule, results also consistent with oxidative resistance. This resistance will ultimately result in failures to control T. castaneum if pyrethroids, such as deltamethrin, cypermethrin or cyfluthrin, are used in the field, even if they are synergised with piperonyl butoxide. The resistance does not jeopardise organophosphorus materials (e.g. fenitrothion, chlorpyrifos-methyl, pirimiphos-methyl, methacrifos) or methoprene.     

The cross-resistance to pyrethrins and eight synthetic pyrethroids,of an organophosphorus-resistant strain of the rust-red flour beetle Tribolium castaneum (herbst)

Comparisons with standard susceptible insects showed that a strain of Tribolium castaneum, with a specific resistance to malathion and its carboxylic ester analogues, had no cross-resistance to topical applications of natural pyrethrins. Another strain of T. castaneum, showing resistance to many organophosphorus (OP) insecticides, was cross-resistant to pyrethrins ( × 34) and eight synthetic pyrethroids also applied topically; least cross-resistance occurred with resmethrin ( × 2.2), bioresmethrin ( × 3.3) and phenothrin ( × 4.0). Generally larger resistance factors were recorded with formulations synergised by piperonyl butoxide (PB). The greatest cross-resistance encountered was with unsynergised tetramethrin ( × 338). Apart from tetramethrin, factors of synergism did not exceed 5.7 with either the susceptible or multi-OP resistant strains. PB antagonised six of the nine pyrethroids against the multi-OP resistant strain. Antagonism also occurred with two of these six, permethrin (cis: trans ratio 1:3) and 5-prop-2-ynylfurfuryl ( 1RS)-cis,trans-chrysanthemate (‘Prothrin’), against the susceptible strain. Considering only formulations without the synergist, the most effective compounds against the susceptible strain, relative to pyrethrins, were bioresmethrin (2.7) and permethrin (2.4). Similarly with the multi-OP resistant strain the most effective compounds were bioresmethrin (28), resmethrin (14) and permethrin (6.6). Thus the LD₅₀ (the dose required to kill 50% of the test species) for bioresmethrin against the resistant strain (0.14 μg) only slightly exceeded the LD₅₀ for pyrethrins against the susceptible strain (0.12 μg).     

Synergised cyfluthrin and cypermethrin as grain protectants on bulk wheat

Duplicate field trials were carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays on samples of treated grain at intervals over 8 or 9 months storage using malathion-resistant strains of insects established that treatments were generally effective. Cyfluthrin (2 mg kg^?1) plus piperonyl butoxide (10 mg kg^?1) and cypermethrin (4 mg kg^?1) plus piperonyl butoxide (10 mg kg^?1) completely controlled two strains of Sitophilus oryzae L. Control of a third strain by the cypermethrin combination was incomplete after 11/2 months and neither controlled a multi-resistant laboratory strain. Both combinations were effective against Rhyzopertha dominica F., Tribolium castaneum Herbst and Ephestia cautella Walker. No natural infestation developed in the treated grain in any silo. Mean residues of cyfluthrin and cypermethrin after 9 months storage were 58% and 52% of the calculated application rates, respectively. Compared with overall concentrations in the wheat, residue levels were higher in bran and pollard and lower in white flour. During baking, residues decreased by up to 29%. Operators experienced respiratory irritation associated with exposure to both combinations and alternative formulations would be required for use of these materials in grain storage.     

Permethrin as a residual insecticide against cockroaches

The pyrethroid permethrin was shown to be active against Blattella germanica, Periplaneta americana and Blatta orientalis. In laboratory tests on plywood panels the best formulation was a 25% wettable powder which showed an initial LC₅₀ of 10 mg m^?2 against B. germanica and lost activity at the weekly rate of 1.9 mg m^?2. An initial deposit of 108 mg m^?2 gave 50% kill after one year. The synergist piperonyl butoxide diminished residual performance. In one field trial, good control was maintained for more than four months with an initial deposit of 50 mg m^?2, the smallest dose used. From this and other trials, the recommended rate of application for general use in long-term control is 100 mg m^?2. A distinctive slow expellent action against B. germanica was seen in field trials.     

Fenitrothion plus (1R)-phenothrin,and pirimiphos-methyl plus carbaryl,as grain protectant combinations for wheat

Duplicate field trials were carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays on samples of treated grain at intervals over 9 months, using malathion-resistant strains of insects, established that treatments were generally effective. Fenitrothion (12 mg kg^?1)+ (1R)-phenothrin (2 mg kg^?1) was more effective than pirimiphos-methyl (6 mg kg^?1) + carbaryl (10 mg kg^?1) against Sitophilus oryzae (L.) and Ephestia cautella (Walker); the order of effectiveness was reversed for S. granarius (L.). Against Rhyzopertha dominica (F.), Tribolium castaneum (Herbst), T. confusum Jackquelin du Val and Oryzaephilus surinamensis (L.), both treatments effectively prevented the production of progeny. The order of persistence was pirimiphos-methyl> (1R)-phenothrin>carbaryl or fenitrothion. During processing from wheat to white bread, residues were reduced by 98% for carbaryl, >44% for (1R)-phenothrin, 98% for fenitrothion and 85% for pirimiphosmethyl.     

Accumulation of malathion residues in grain stored on malathion-treated wood surfaces

Laboratory studies were conducted to determine whether insecticides applied to storage structures are able to move past a single layer of grain kernels to give adequate control of stored-grain insects. The extent of uptake of insecticides was assessed on three layers of wheat in contact with wood surfaces treated with malathion 836 g litre^?1 e.c. at 1–0 g a.i. m^?2 using chemical and biological methods at predetermined time intervals. There was a progressive uptake of malathion beyond the layer directly in contact with the treated surfaces and the uptake depended on the duration of storage. After 8 weeks a sufficient amount of malathion accumulated on the top layer of grain kernels to cause 100% mortality of adult Tribolium castaneum (Herbst).     

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     

昆虫对拟除虫菊酯类杀虫剂的代谢抗性机制研究进展

随着拟除虫菊酯类杀虫剂在卫生和农业害虫防治中的广泛应用,昆虫对此类杀虫剂产生抗性的报道越来越多。目前已明确昆虫对拟除虫菊酯类杀虫剂的抗性机制包括表皮穿透率下降、靶标抗性以及代谢抗性,其中代谢抗性机制较为普遍,而且其与昆虫对多种杀虫剂的交互抗性关系密切。目前,随着基因组、转录组以及蛋白质组学等新技术的发展及应用,昆虫对拟除虫菊酯类杀虫剂的代谢抗性机制研究也取得了很多新进展。昆虫体内细胞色素P450酶（P450s）、羧酸酯酶（CarE）及谷胱甘肽S-转移酶（GSTs）等重要解毒酶系的改变均与昆虫对拟除虫菊酯类杀虫剂的代谢抗性有关,其中这3类解毒酶的活性及相关基因表达量的变化是昆虫对此类杀虫剂产生代谢抗性的主要原因。明确昆虫对拟除虫菊酯类杀虫剂的代谢抗性机制,对合理使用此类杀虫剂及延缓抗药性的产生均具有重要意义。本文在总结拟除虫菊酯类杀虫剂代谢路径及相关生物酶研究概况的基础上,综述了近年来有关昆虫对此类杀虫剂代谢抗性机制研究的主要进展。     

防治金银花尺蠖幼虫高效药剂的筛选及应用评价

为筛选防治金银花尺蠖Heterolocha jinyinhuaphaga Chu幼虫的高效、低残留杀虫剂,采用浸虫法和浸叶法分别测定了13种杀虫剂对金银花尺蠖幼虫的触杀毒力和胃毒毒力,筛选出高活性药剂,并对筛选的药剂进行田间防效试验及检测其在金银花中的农药残留量。毒力测定结果表明,甲维盐对金银花尺蠖2龄和4龄幼虫的毒力最高,触杀毒力LC_ct50分别为0.291、0.391 mg/L,胃毒毒力LCst50分别为0.081、0.275 mg/L;多杀菌素、氟铃脲、氯虫苯甲酰胺药剂对金银花尺蠖幼虫也表现出较高的致毒作用。田间药效试验表明,有效成分用量2.25 g （a.i.）/hm²的甲维盐、有效成分用量11.25 g （a.i.）/hm²的多杀菌素对金银花尺蠖幼虫均有极好的防治效果,药后7 d防治效果分别为96.39%和93.13%,表明甲维盐和多杀菌素是防治金银花尺蠖幼虫的特效药剂。残留检测分析结果表明,有效成分用量6、12 g （a.i.）/hm²的甲维盐喷雾处理3 d后,金银花中农药残留量分别为0.0219、0.0725 mg/kg,7 d后分别为0.0070、0.0168 mg/kg。     

The role of glutathione S-transferases in the detoxification of some organophosphorus insecticides in larvae and pupae of the yellow mealworm,Tenebrio molitor (Coleoptera: Tenebrionidae)

The correlation between the natural levels of glutathione S-transferase (GST) and the tolerance to the organophosphorus insecticides parathion-methyl and paraoxon-methyl, as well as the interaction of affinity-purified enzyme and the insecticides were investigated in order to collect further information on the role of the glutathione S-transferase system as a mechanism of defence against insecticides in insects. The studies were carried out on the larvae and pupae of the coleopteran Tenebrio molitor L, which exhibit varying natural levels of GST activity. Stage-dependent susceptibility of the insect against insecticides was observed during the first 24 h. However, 48 h after treatment, the KD₅₀ value increased significantly due to the recovery of some individuals. Simultaneous injection of insecticide with compounds which inhibit GST activity in vitro caused an alteration in susceptibility of insects 24 or 48 h post-treatment, depending on stage and insecticide used. Inhibition studies combined with competitive fluorescence spectroscopy revealed that the insecticides probably bind to the active site of the enzyme, thus inhibiting its activity towards 1-chloro-2,4-dinitrobenzene in a competitive manner. High-performance liquid chromatography and gas chromatography revealed that T molitor GST catalyses the conjugation of the insecticides studied to a reduced form of glutathione (GSH). From the above experimental results, it is considered that GST offers a protection against the organophosphorus insecticides studied by active site binding and subsequent conjugation with GSH. © 2001 Society of Chemical Industry     

A comparison of permethrin and methomyl insecticides for the control of a multiresistant strain of houseflies (Musca domestica)

A methomyl sugar bait formulation and permethrin residual spray were compared for the control of a multi-insecticide resistant strain of housefly in a UK pig farm. The methomyl was applied as a granular scatter bait at the manufacturer's recommended rate of 25 mg m^?2 active ingredient (a.i.) to the treated floor area. Permethrin was applied at 32, 64 and 128 mg m^?2 a.i. to structural surfaces. The highest deposit rate of permethrin used was four times that recommended by the manufacturer for the control of flying insects. The methomyl bait gave effective control but the permethrin spray failed at all deposit rates tested. The use of permethrin increased resistance to this compound at the KD50 level from x 13 to x 560 within 10 weeks and significantly increased the proportion of flies resistant to natural pyrethrins synergised with piperonyl butoxide (P<0.01).     

The effects of temperature and humidity on the toxicity of three organophosphorus insecticides to adult Oryzaephilus surinamensis (L.)

The toxicities, to a laboratory susceptible strain and to a resistant strain of Oryzaephilus surinamensis (L.), of water-dispersible powder formulations of pirimiphos-methyl, fenitrothion or chlorpyrifos-methyl under constant conditions of 25°C and 70% r. h. were compared to the toxicities when the insects were exposed to a diurnal cycle of 12.5–20–12.5°C and 70–50–70% r. h. to simulate grain store conditions in the UK during spring and autumn. All the insecticides were more effective at 25°C and 70% r. h. The LD₅₀ values for the susceptible strain were low, being 4.4 and 1.4 mg m^?2 at 12.5-20°C and 25°C, respectively, for chlorpyrifos-methyl, 18.3 and 4.1 mg m^?2, respectively, for pirimiphos-methyl, and 4.0 and < 1.O mg m^?2, respectively, for fenitrothion. The LD₅₀ values obtained from the two sets of environmental conditions for a resistant strain (484) differed by factors of 1.8 for chlorpyrifos-methyl, 4.8 for pirimiphos-methyl, and 7.3 for fenitrothion. Toxicity studies were also made with chlorpyrifos-methyl under various constant conditions of temperature and humidity from 5–30°C (5°C intervals) and 30, 50, 70 and 90% r. h., and also at O°C and 60% r. h. Chlorpyrifos-methyl was very effective and there was little or no cross resistance to chlorpyrifos-methyl in the resistant strain. From 15 to 30°C, mortality was high, and differences in mortality at the LD₅₀ level for the various humidities were slight, but there was a decrease in mortality with decreasing humidity at any one temperature, in particular, at 5°C, 50 and 70% r. h., and 10°C and 50% r. h. Chlorpyrifosmethyl was more toxic to both strains at the highest humidity (90%) throughout the whole temperature range. The LD₅₀ values for each strain decreased at each temperature as the water vapour concentration was increased. At O°C and 60% r. h., all the insects from both strains died but the cause of death was not clear.     

Residue behaviour of fenvalerate,tau-fluvalinate,lambda-cyhalothrin and monocrotophos in eggplant (Solanum melongena L.) fruits

The persistence patterns of three synthetic pyrethroids—fenvalerate, tau-fluvalinate, lambda-cyhalothrin—and an organophosphorus insecticide, monocrotophos, on eggplant (Solanum melongena L.) have been evaluated. The extractable residues ranged from 0.05 to 0.45, 0.01 to 0.40, 0.003 to 0.09 and 0.09 to 0.32 μg g^?1 for fenvalerate, tau-fluvalinate, lambda-cyhalothrin and monocrotophos, respectively. Fenvalerate was the most persistent among the four, followed by monocrotophos, lambda-cyhalothrin and tau-fluvalinate. The Maximum Residue Limit (MRL) of these pesticides on S. melongena has not yet been documented. The present data may be useful for establishing MRL and assessing the amount of pesticide residues in this vegetable.