Activity of abamectin against larval stages of Spodoptera littoralis boisduval and Heliothis armigera hübner (Lepidoptera: Noctuidae) and possible mechanisms determining differential toxicity

Marked changes in the relative toxicity of topically-applied abamectin were found between larval instars of Spodoptera littoralis, toxicity decreasing up to the fifth instar but increasing over 500-fold (at LD₅₀ level) in the sixth instar. By contrast, the toxicity of abamectin remained constant from fifth to sixth instar Heliothis armigera and there was an increase in the toxicity of two chemically unrelated insecticides, malathion (4-fold) and lambda-cyhalothrin (2.5-fold), from fifth to sixth instar S. littoralis. Prior topical application or injection of the microsomal oxidase inhibitor, piperonyl butoxide (PB) increased the toxicity of abamectin (6–8 and 16-fold respectively) against fifth instar S. littoralis, while topically-applied PB increased the proportion of radioactivity present as abamectin in the ventral nerve cord of this instar following topical application with [³H]abamectin. Topically-applied PB also enhanced the toxicity of abamectin against third (4-fold) and fourth instar (5-fold) S. littoralis but had no significant effect on sixth instar S. littoralis, fifth instar H. armigera, or on the toxicity of malathion and lambda-cyhalothrin against fifth instar S. littoralis. Topical application of the esterase inhibitor, S,S,S-tributyl phosphorothioate (DEF) significantly increased the toxicity of abamectin at the LD₅₀ level (3-fold) against fifth instar S. littoralis. The toxicity of injected abamectin against fifth instar S. littoralis was greater (20-fold) than with topical application but injected abamectin was less toxic (2-fold) against sixth instar S. littoralis and had no significant effect on fifth instar H. armigera. It is suggested that differential toxicity of abamectin is due in part to greater metabolism and reduced penetration in fifth instar S. littoralis than in sixth instar S. littoralis or fifth instar H. armigera.     

Toxicity of chlordimeform and amitraz to the egyptian cotton leafworm (Spodoptera littoralis) and the tobacco budworm (Heliothis virescens)

The relative toxicity (μg a.i. g^?1 body wt) of the formamidine insecticide chlordimeform (CDM) and the triazapentadiene insecticide amitraz was examined in two species of noctuid moth Spodoptera littoralis and Heliothis virescens. When applied topically, there was an unexpected and marked difference in the toxicity of CDM base and its hydrochloride to adults of both species, the salt being appreciably more toxic. For H. virescens at least, this difference in toxicity could not be explained by differences in penetration. This trend was reversed for larval instars of S. littoralis; while there was relatively little difference in the toxicity of the base to adult and larval stages, the salt was at least 1000-fold more toxic to adults than to larvae. N¹-Demethylchlordimeform (DCDM) was the only metabolite of CDM to show biological activity against either species, but was much less toxic than the parent compound. Amitraz was far less toxic than either CDM or DCDM; like the CDM salt, it appeared to be more toxic to adult than larval stages of S. littoralis. Application of piperonyl butoxide significantly increased the toxicity of the CDM salt, DCDM and amitraz to adult H. virescens, the synergist being particularly effective with DCDM and amitraz. In contrast, piperonyl butoxide had no significant effect on the toxicity of DCDM, and slightly antagonised the toxicity of DCDM to fourth-instar larvae of S. littoralis.     

烟芽夜蛾囊泡病毒3h株对草地贪夜蛾幼虫的感染特性及对其生长发育的影响

为寻找有效防控外来入侵物种草地贪夜蛾Spodoptera frugiperda的技术,以烟芽夜蛾囊泡病毒3h株(Heliothis virescens ascovirus 3h,HvAV-3h)为研究对象,通过测定不同龄期草地贪夜蛾幼虫口服或针刺感染HvAV-3h后的死亡率、存活时间、取食量及体重,分析该毒株对草地贪夜蛾幼虫的感染特性及对其生长发育的影响。结果显示,草地贪夜蛾1、2龄幼虫口服HvAV-3h后的校正死亡率分别为9.22%和0,3～6龄幼虫针刺感染HvAV-3h后的校正死亡率则高达100.00%,感染HvAV-3h的幼虫均在幼虫期或蛹期死亡。3～5龄幼虫针刺感染HvAV-3h后的存活时间明显长于健康幼虫;3～6龄幼虫针刺感染HvAV-3h后其体重和取食量均受到不同程度的抑制作用,体重抑制率分别为67.79%、41.68%、16.31%和10.30%,总取食量抑制率分别为57.80%、33.90%、17.42%和41.82%;其中3龄幼虫针刺感染HvAV-3h后的体重和取食量被显著抑制,且蜕皮困难,最终在幼虫期死亡;部分4～6龄感染HvAV-3h幼虫能够完成化蛹,但是均无法羽化。表明HvAV-3h感染能够有效控制草地贪夜蛾幼虫,有望开发为草地贪夜蛾的生防制剂。     

Entomopathogenic nematodes for the management of Agrotis ipsilon: effect of instar, nematode species and nematode production method

BACKGROUND: Previous laboratory studies have indicated the potential of some entomopathogenic nematode (EPN) species for the control of larvae of the black cutworm (BCW). To determine the most promising EPN species and the most susceptible BCW stages, a more in‐depth evaluation of seven EPN species against different BCW instars was carried out, the efficacies of in vitro‐ and in vivo‐produced EPNs were compared and the suitability of BCW instars for EPN reproduction was examined. RESULTS: Heterorhabditis megidis was the most virulent species, irrespective of larval stage in small arenas, followed most often by H. bacteriophora. In pots with grass, Steinernema carpocapsae tended to be the most virulent species, followed by H. bacteriophora, H. megidis and S. riobrave. Fourth and/or fifth instars were the most susceptible stages to most EPN species, and pupae the least susceptible. Furthermore, H. bacteriophora, H. megidis and S. carpocapsae successfully reproduced in fifth and sixth instars and pupae. In vivo‐produced H. megidis and S. carpocapsae controlled fifth instars better than the corresponding in vitro‐produced products; production method did not affect H. bacteriophora and S. riobrave efficacy. CONCLUSIONS: Several in vitro‐produced commercial EPN strains were highly virulent to BCW and warrant further testing under field conditions, along with some in vivo‐produced strains. Copyright © 2011 Society of Chemical Industry     

Laboratory and field evaluations of rhodojaponin-III against the imported cabbage worm Pieris rapae (L.) (Lepidoptera: Pieridae)

The activity of rhodojaponin-III (R-III), a grayanoid diterpene compound isolated from Rhododendron molle G. Don flowers, was determined under laboratory and field conditions as an antifeedant, stomach poison, contact toxicant and insect growth inhibitor against Pieris rapae (L.) larvae. The median antifeedant concentration (AFC(50)) values in no-choice leaf disc tests were 1.16 and 15.85 mg L(-1) at 24 h after treatment when tested against third and fifth instars respectively. The median lethal concentration (LC(50)) values in leaf disc tests were 2.84 and 9.53 mg L(-1) at 96 h after treatment against third and fifth instars respectively. R-III showed an almost 30 times higher contact toxicity against third instars than for fifth instars, and the median lethal dose (LD(50)) values for topical application were 1.18 and 34.09 mg kg(-1) at 72 h after treatment respectively. R-III disrupted the development of larvae to pupae or adults with median concentration for inhibiting growth (IC(50)) values of only 1.36 mg L(-1) for third instars and 11.28 mg L(-1) for fifth instars. In field trials, a greater than 80% reduction in the adjusted larval numbers was obtained against P. rapae 14 days after treatment when Rhodo 0.1% EC, a commercial botanical insecticide based on R-III, was applied at both 937.5 and 625 mL ha(-1). These results suggest that further research to develop R-III, and extracts from R. molle, as biorational pesticides or as lead compounds for integrated pest management deserve consideration.     

Why does DDT toxicity change after a blood meal in adult female Culex pipiens?

The toxicity of topically applied DDT to adult female anautogenous mosquitoes (Culex pipiens L.) showed dramatic variations in blood-fed insects. It decreased very rapidly about twofold to a minimum at 24 hr after a blood meal, then increased within 72 hr back to values typical of non-blood fed insects. A comparison of the metabolism of [¹⁴C]DDT in vivo revealed an increase in DDT dehydrochlorination to DDE at 72 hr after a blood meal, but this increase was not responsible for the variations in DDT toxicity at 24 hr. Changes in penetration rates were not observed and changes in the distribution of DDT could likewise not be related to the short period of decreased toxicity of DDT. Fenvalerate and trans-permethrin, two pyrethroid insecticides which are believed to have a mode of action similar to that of DDT, were also significantly less toxic 24 hr after a blood meal. By contrast, the cyclodiene insecticide aldrin and the carbamate insecticide propoxur were not less toxic 24 hr after a blood meal. The results suggest that after a blood meal an unidentified and transient change in C. pipiens specifically decreases DDT/pyrethroid toxicity. A hypothesis concerning this transient change is advanced. The results illustrate the difficulties in explaining physiological changes in insecticide toxicity.     

Insecticide resistance status of Aedes aegypti (L.) from Colombia

BACKGROUND: To evaluate the insecticide susceptibility status of Aedes aegypti (L.) in Colombia, and as part of the National Network of Insecticide Resistance Surveillance, 12 mosquito populations were assessed for resistance to pyrethroids, organophosphates and DDT. Bioassays were performed using WHO and CDC methodologies. The underlying resistance mechanisms were investigated through biochemical assays and RT‐PCR. RESULTS: All mosquito populations were susceptible to malathion, deltamethrin and cyfluthrin, and highly resistant to DDT and etofenprox. Resistance to lambda‐cyhalothrin, permethrin and fenitrothion ranged from moderate to high in some populations from Chocó and Putumayo states. In Antioquia state, the Santa Fe population was resistant to fenitrothion. Biochemical assays showed high levels of both cytochrome P450 monooxygenases (CYP) and non‐specific esterases (NSE) in some of the fenitrothion‐ and pyrethroid‐resistant populations. All populations showed high levels of glutathione‐S‐transferase (GST) activity. GSTe2 gene was found overexpressed in DDT‐resistant populations compared with Rockefeller susceptible strain. CONCLUSIONS: Differences in insecticide resistance status were observed between insecticides and localities. Although the biochemical assay results suggest that CYP and NSE could play an important role in the pyrethroid and fenitrothion resistance detected, other mechanisms remain to be investigated, including knockdown resistance. Resistance to DDT was high in all populations, and GST activity is probably the main enzymatic mechanism associated with this resistance. The results of this study provide baseline data on insecticide resistance in Colombian A. aegypti populations, and will allow comparison of changes in susceptibility status in this vector over time. Copyright © 2011 Society of Chemical Industry     

The biochemistry of insecticide resistance in Anopheles sacharovi: Comparative studies with a range of insecticide susceptible and resistant Anopheles and Culex species

Fourth instar larvae, the progeny from wild-caught Anopheles sacharovi females, were subjected to a number of biochemical tests and the results were compared to those from similar tests on laboratory insecticide resistant and susceptible strains of anopheline and culicine mosquitoes. DDT resistance in An. sacharovi is associated with the ability to rapidly metabolise DDT to DDE. The organophosphorus and carbamate resistance was not associated with quantitative changes in esterases, multifunction oxidases, or glutathione S-transferase. The acetylcholinesterase was less sensitive to malaoxon and propoxur than laboratory susceptible An. albimanus, and plots of inhibition suggest that the population was polymorphic for more than one form of acetylcholinesterase. Metabolism studies on malathion and pirimiphos methyl did not indicate resistance due to increased metabolism. There was no evidence of penetration barriers contributing to resistance to either DDT or malathion, and there was no indication of any resistance to pirimiphos methyl in our tests.     

Mechanisms of DDT resistance in larvae of the mosquito Aedes aegypti L

Larvae of eight strains of Aedes aegypti were exposed to DDT and compared for resistance, DDT uptake, in-vivo breakdown of DDT and residual unmetabolised DDT. Resistance varied widely between strains, three being fully susceptible, two almost immune and three of intermediate resistance. Breakdown of DDT by dehydrochlorination to 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (pp'-DDE) occurred in all strains and was greater in the five resistant types, but there was no significant correlation between the extent of breakdown in the resistant strains and the level of resistance. Moreover the overall difference between susceptible and resistant strains disappeared when they were compared at a low, almost sublethal, concentration of DDT. Larvae of resistant strains carried a greater absolute quantity of unmetabolised DDT in the body and were able to tolerate levels of DDT that were lethal to susceptible larvae. However the two most resistant strains (T8 and B51) contained significantly less DDT plus pp'-DDE than strains of intermediate resistance (T30 and BSJ) from which they had been derived. Addition of the synergist chlorfenethol to DDT increased its knockdown effect on all resistant strains, suggesting that dehydrochlorination was a factor in resistance. Three strains, two DDT-resistant and one DDT-susceptible, were tested with 1,1-bis(4-ethoxyphenyl)-2,2-dimethylpropane (I), an insecticide that cannot be dehydrochlorinated. All the strains were relatively tolerant to it although the DDT-susceptible strains were less tolerant. Addition of the synergist sesamex decreased the level of tolerance to I in all strains which suggested that microsomal oxidation made some contribution to it. It is concluded that three factors contribute to larval DDT resistance in A. aegypti; (a) increased metabolism to pp'-DDE; (b) increased tolerance to unmetabolised internal DDT; and (c) reduced content of DDT+pp'-DDE (only in the most resistant strains and due either to reduced absorption or increased excretion). These factors are discussed in relation to known larval resistance genes R^DDT1 and y.     

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     

Glutathione Depletion and Insecticide Synergism in Triatoma infestans produced by the Butyl Ester of Buthionine Sulfoximine

The butyl ester of buthionine sulfoximine (BBSO) applied topically to the nymph V stage of Triatoma infestans (Klug) caused glutathione depletion which was maintained for four days after treatment. Topical pre-treatment of nymph V with BBSO significantly synergised the toxicity of DDT and fenitrothion to T. infestans.     

Insecticide resistance in the tropical bedbug Cimex hemipterus

Insecticide resistance in the bedbug Cimex hemipterus was investigated using 4211 bedbugs collected from three districts of Sri Lanka. Insecticide bioassays were carried out with discriminating dosages of deltamethrin, permethrin, DDT, malathion, and propoxur. Activity levels of insecticide metabolizing enzymes and the insecticide target site acetylcholinesterase were monitored using biochemical assays. Percentage survivals after DDT, malathion, and propoxur exposure were 41-88%, 18-64%, and 11-41%, respectively. For deltamethrin and permethrin, KT₅₀/KT₉₀ (time to knock-down 50%/90% of the population) values were 0.5-24/1.0-58 and 1.3-10/2.5-47 h, respectively. Both elevated esterase and malathion carboxylesterase mechanisms were present in bedbug populations. Monooxygenase levels were heterogeneous. Organophosphate and carbamate target site acetylcholinesterase, was insensitive in 29-44% of the populations. High DDT resistance was probably due to glutathione S-transferases. Malathion carboxylesterases are mainly responsible for high malathion resistance. High tolerance to both DDT and pyrethroids suggests the presence of ‘kdr’ type resistance mechanism in one population.     

Effect of pyriproxyfen,a juvenile hormone mimic,on egg hatch,nymph development,adult emergence and reproduction of the Asian citrus psyllid,Diaphorina citri Kuwayama

BACKGROUND: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is a vector of bacteria presumably responsible for huanglongbing (HLB) disease in citrus. In this laboratory study, an investigation was made of the activity of pyriproxyfen, a juvenile hormone mimic, on ACP eggs, nymphs and adults to evaluate its potential as a biorational insecticide for inclusion in an integrated pest management (IPM) program for ACP. RESULTS: Irrespective of egg age, timing or method of treatment, a significantly lower percentage of eggs (5–29%) hatched after exposure to 64 and 128 µg mL^?1 of pyriproxyfen. Only 0–36% of early instars (first, second and third) and 25–74% of late instars (fourth and fifth) survived to adults following exposure to 16, 32 and 64 µg mL^?1 of pyriproxyfen. However, 15–20% of adults that emerged following treatment as late instars exhibited morphological abnormalities. Furthermore, pyriproxyfen adversely affected reproduction (fecundity and fertility) of adults that emerged from treated fifth instars or that were treated topically with 0.04 µg as adults. CONCLUSIONS: Application of pyriproxyfen at 64 µg mL^?1 resulted in greater inhibition of egg hatch and suppression of adult emergence compared with lower rates. Pyriproxyfen also markedly reduced female fecundity and egg viability for adults that were exposed either as fifth instars or as newly emerged adults. The ovicidal, larvicidal and reproductive effects against ACP suggest that pyriproxyfen is suitable for integration into an IPM program for ACP. Copyright © 2009 Society of Chemical Industry     

Toxicity of selected insecticides to the two-spot ladybird <Emphasis Type="Italic">Adalia bipunctata</Emphasis>

The toxicity of pirimicarb, imidacloprid, dimethoate, lambda-cyhalothrin, flonicamid and spinosad to the two-spot ladybird, Adalia bipunctata, was evaluated in a laboratory study. Susceptibility of fourth instars and female adults was assessed by measuring toxicity via residual contact and ingestion through feeding on contaminated green peach aphids (Myzus persicae). Flonicamid and spinosad had no lethal effects on larvae and female adults. Pirimicarb was harmless to the predator by ingestion exposure but showed some residual toxicity at high concentrations to both larval and adult stages. Imidacloprid was highly toxic to the larval stage by residual and ingestion exposure but caused very low adult mortality when ingested through contaminated prey. Dimethoate and lambda-cyhalothrin were highly toxic to both the larval and adult stages of the ladybird. Our findings indicate that pest management programs in agricultural crops using dimethoate, lambda-cyhalothrin and, to a lesser degree, imidacloprid, are detrimental to A. bipunctata, whereas pirimicarb, flonicamid and spinosad are more compatible with the use of this predator.     

Synergism of insecticidal action and effects on detoxifying enzymes in vivo of lambda-cyhalothrin and malathion by some nitrogen heterocycles in resistant and susceptible strains of Tribolium castaneum

The interactions of the synthetic pyrethroid, lambda-cyhalothrin and malathion were studied with purines, pyrimidines, caffeine and some other related nitrogenous compounds in resistant and susceptible strains of Triboliurn castaneum (Herbst.) The results were compared with those obtained with a known synergist, piperonyl butoxide (PBO) and precocene I. Adenine, cytosine, guanine, thymine and uracil synergised lambda-cyhalothrin, especially in the susceptible strain, with maximum effect at a 1:1 mass ratio, with the effect decreasing with increasing proportion of the heterocycle. The order of synergism of lambda-cyhalothrin was; precocene I > PBO > the nitrogenous compounds, in both resistant and susceptible strains. On the other hand, caffeine (lethal effect increased about twice), barbital (about twice), isobarbituric acid (less than twice) and bromacil (up to eight times) synergised malathion in malathion-resistant strains and antagonised in the susceptible strains. Total in-vivo esterases, carbox-ylesterases and cytochrome P₄₅₀ of susceptible and resistant strains showed significantly increased activity or content when treated with either insecticide plus a heterocyclic compound. Exceptions were with bromacil and malathion and for the malathion-specific strain, Kano-C with malathion and the N-heterocycles.     

Effect of the acylurea insect growth regulator teflubenzuron on the endo-larval stages of the hymenopteran parasitoids Cotesia plutellae and Diadegma semiclausum in a susceptible and an acylurea-resistant strain of Plutella xylostella

The toxicity of the acylurea, teflubenzuron, was assessed against larval stages of the hymenopteran parasitoids, Cotesia plutellae Kurdjumov and Diadegma semiclausum Hellén in a susceptible laboratory strain and a teflubenzuron-resistant field strain of the diamondback moth, Plutella xylostella L. In fourth-instar hosts (L4), when both parasitoid species were in their final larval instar, teflubenzuron significantly (P < 0.05) reduced emergence of adult D. semiclausum but had no significant (P > 0.05) effect on C. plutellae, although a small proportion of the latter were unable to reproduce. Treatment of L4 hosts with teflubenzuron ( > LD₅₀) had no significant (P > 0.05) effect on the fecundity of surviving females of D. semiclausum. Similar differential toxicity with teflubenzuron was observed in L2 hosts, when parasitoids were at the egg or early larval instar stage. There was no apparent increased effect of teflubenzuron on either species of parasitoid when highly resistant (c. 4000-fold) L2 hosts (field strain) were treated with concentrations of teflubenzuron two to three orders of magnitude greater than in equivalent experiments with the susceptible host strain. This suggests that host resistance to teflubenzuron confers some protection to both species of parasitoid. Uptake experiments with [¹⁴C]teflubenzuron showed that accumulation of radioactivity was much greater in D. semiclausum than in C. plutellae and this may account for the differential toxicity observed. The results are discussed in relation to the field status of these parasitoid species. The influence of insecticide resistance in the host on endo-larval parasitoids is also considered.     

An electrophysiological investigation of the susceptible (cooper) and resistant (kdr; super-kdr) strains of the adult housefly,Musca domestica L

The electrical activity of abdominal nerves of the housefly, Musca domestica L., was used as a bioassay to study nerve sensitivity to DDT and deltamethrin in susceptible (Cooper) and resistant (kdr, super-kdr) strains. By this technique the resistant strains were less sensitive (approximately 10 000-fold) than Cooper, but the bioassay could not distinguish between super-kdr and kdr in their responses to either compound and so could not account for the greater resistance shown by flies with super-kdr above kdr flies when these insecticides are applied topically. Although factors other than nerve insensitivity may be involved, the compounds were applied to the preparation in aqueous saline solutions at, or close to, their solubility limits and this could have masked differences in responses of nerves from the resistant strains.     

Membrane partitioning of organophosphorus and organochlorine insecticides and its implications for mechanisms of toxicity

Partition coefficients of organophosphorus and organochlorine insecticides were determined in several types of membrane. Insecticide partitioning varied among the membranes under study, depending on temperature, cholesterol content and on the physico-chemical profiles of membrane components and the insecticides themselves. The maximal partitions for DDT, lindane, parathion and malathion in egg phosphatidylcholine bilayers over the temperature range from 10 to 37°C (at which the lipid is in the liquid-crystalline state) were about 260000, 2000, 1000 and 120, respectively. Incorporation of 50 mol% cholesterol in egg phosphatidylcholine bilayers dramatically decreased the partition and almost abolished the temperature effect. First-order phase transitions of dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines (DMPC, DPPC and DSPC) were accompanied by a sharp increase in insecticide partition. Furthermore, the insecticides under study were more easily accommodated in bilayers of short-aliphatic-chain lipids, since higher values of partition were obtained in DMPC bilayers. Partition values in native membranes depended considerably on the membrane type and composition and were higher in sarcoplasmic reticulum (SR) and mitochondria than in brain microsomes, myelin and erythrocytes. Identical results were obtained in related liposomes of total extracted lipids, although the absolute partitions showed decreased values. In general, the incorporation of insecticides correlated reasonably with the cholesterol content of the membranes. The order of partitioning of the above insecticides did not run parallel with their toxicity to mammals and, both in model and in native membranes, followed the sequence: DDT ? lindane > parathion > malathion.     

杀虫剂对甜菜夜蛾不同世代及幼虫龄期的毒力变化

甜菜夜蛾 ( Spodoptera exigua Hübner)属鳞翅目夜蛾科 ,是一种世界性的农业害虫。该虫为杂食性 ,寄主范围广[1 ] 。自 80年代以来 ,由于种植结构及栽培管理方式不当、气候条件、农药对天敌的影响、抗药性、迁飞性等各方面的因素 ,致使甜菜夜蛾发生呈上升趋势。目前 ,对甜菜夜蛾的研究主要局限在生物学、生态学、防治等方面 ,而对其抗药性规律尚缺乏深入研究。作者主要研究了杀虫剂对甜菜夜蛾的不同发生世代和不同幼虫龄期的毒力变化 ,对该虫的化学防治有一定指导意义。1　材料与方法1 .1　供试药剂氟啶脲 ,92 .5 %原药 (日本石原产业株式…     

Knockdown by pyrethroids: Its role in the intoxication process

Using techniques for treating the insects unanaesthetised, knockdown of aduit Musca domestica by pyrethrin I applied topically to or injected into the thorax was assessed by measuring the ED₅₀s on 13 occasions 1 min-48 h after treatment. From 1 min to approximately 1 h after treatment, ED₅₀s for topical application decreased quickly with increasing time. During this “knockdown phase” ED₅₀ values were probably determined mainly by rate of penetration of the insecticide into the insect, but the rate of elimination of the insecticide probably determined the increasing ED₅₀ values during the “recovery phase” which followed. ED₅₀s for injected pyrethrin I were initially much smaller than after topical application but increased continuously until 24 h after treatment. From 100 min onwards ED₅₀s by topical application and injection were similar. These results indicate (1) that the site affected during knockdown is within the insect rather than superficial, and (2) that detoxication and excretion processes determine the ultimate toxicity of the insecticide apparently independently of the method of treatment. Additional tests with a strain of flies having the penetration delaying factor and with the cockroach Periplaneta americana L. supported these conclusions. Speed of knockdown after topical treatment was also affected by the site of application and the solvent in which pyrethrin I was applied. Bioresmethrin was about as effective as pyrethrin I in knocking down flies when applied topically or when injected, but because the ED₅₀ increased very little during the recovery phase it was ultimately much more toxic.