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PubMed2001

Natural products as insecticides: the biology, biochemistry and quantitative structure-activity relationships of spinosyns and spinosoids.

The spinosyns, a novel family of insecticidal macrocyclic lactones, are active on a wide variety of insect pests, especially lepidopterans and dipterans. The biological activity of a mixture (spinosad; Tracer, Spin-Tor, Success) of the two most abundant spinosyns (spinosyns A and D) against pest insects is on a par with that of many pyrethroid insecticides. The spinosyns also exhibit a very favorable environmental and toxicological profile, and possess a mode of action that appears unique, with studies to date suggesting that both nicotinic and gamma-aminobutryic acid receptor functions are altered in a novel manner. Compared to pyrethroids such as cypermethrin, spinosyn A is slow to penetrate into insect larvae such as tobacco budworm larvae (Heliothis virescens); however, once inside the insect, spinosyn A is not readily metabolized. To date, more than 20 spinosyns and more than 800 spinosoids (semi-synthetic analogs) have been isolated or synthesized, respectively. Artificial neural network-based quantitative structure activity relationship (QSAR) studies for the spinosyns suggested that modification of the 2',3',4'-tri-O-methylrhamnosyl moiety could improve activity and several spinosoids incorporating these modifications exhibited markedly improved lepidopteran activity compared to spinosad. Multiple linear regression-based QSAR studies also suggest that whole molecule properties such as CLogP and MOPAC dipole moment can explain much of the biological activity observed for the spinosyns and closely related spinosoids.

Animals↗
PubMed2001

Residues of zeta-cypermethrin in bovine tissues and milk following pour-on and spray application.

The depletion of zeta-cypermethrin residues in bovine tissues and milk was studied. Beef cattle were treated three times at 3-week intervals with 1 ml 10 kg-1 body weight of a 25 g litre-1 or 50 g litre-1 pour-on formulation (2.5 and 5.0 mg zeta-cypermethrin kg-1 body weight) or 100 mg kg-1 spray to simulate a likely worst-case treatment regime. Friesian and Jersey dairy cows were treated once with 2.5 mg zeta-cypermethrin kg-1 in a pour-on formulation. Muscle, liver and kidney residue concentrations were generally less than the limit of detection (LOD = 0.01 mg kg-1). Residues in renal-fat and back-fat samples from animals treated with 2.5 mg kg-1 all exceeded the limit of quantitation (LOQ = 0.05 mg kg-1), peaking at 10 days after treatment. Only two of five kidney fat samples were above the LOQ after 34 days, but none of the back-fat samples exceeded the LOQ at 28 days after treatment. Following spray treatments, fat residues were detectable in some animals but were below the LOQ at all sampling intervals. Zeta-cypermethrin was quantifiable (LOQ = 0.01 mg kg-1) in only one whole-milk sample from the Friesian cows (0.015 mg kg-1, 2 days after treatment). In whole milk from Jersey cows, the mean concentration of zeta-cypermethrin peaked 1 day after treatment, at 0.015 mg kg-1, and the highest individual sample concentration was 0.025 mg kg-1 at 3 days after treatment. Residues in milk were not quantifiable beginning 4 days after treatment. The mean concentrations of zeta-cypermethrin in milk fat from Friesian and Jersey cows peaked two days after treatment at 0.197 mg kg-1 and 0.377 mg kg-1, respectively, and the highest individual sample concentrations were 2 days after treatment at 0.47 mg kg-1 and 0.98 mg kg-1, respectively.

Adipose Tissue↗
PubMed2001

Pyrethroid resistance and cross-resistance in the German cockroach, Blattella germanica (L).

A German cockroach (Blatella germanica (L)) strain, Apyr-R, was collected from Opelika, Alabama after control failures with pyrethroid insecticides. Levels of resistance to permethrin and deltamethrin in Apyr-R (97- and 480-fold, respectively, compared with a susceptible strain, ACY) were partially or mostly suppressed by piperonyl butoxide (PBO) and S,S,S,-tributylphosphorotrithioate (DEF), suggesting that P450 monooxygenases and hydrolases are involved in resistance to these two pyrethroids in Apyr-R. However, incomplete suppression of pyrethroid resistance with PBO and DEF implies that one or more additional mechanisms are involved in resistance. Injection, compared with topical application, resulted in 43- and 48-fold increases in toxicity of permethrin in ACY and Apyr-R, respectively. Similarly, injection increased the toxicity of deltamethrin 27-fold in ACY and 28-fold in Apyr-R. These data indicate that cuticular penetration is one of the obstacles for the effectiveness of pyrethroids against German cockroaches. However, injection did not change the levels of resistance to either permethrin or deltamethrin, suggesting that a decrease in the rate of cuticular penetration may not play an important role in pyrethroid resistance in Apyr-R. Apyr-R showed cross-resistance to imidacloprid, with a resistance ratio of 10. PBO treatment resulted in no significant change in the toxicity of imidacloprid, implying that P450 monooxygenase-mediated detoxication is not the mechanism responsible for cross-resistance. Apyr-R showed no cross-resistance to spinosad, although spinosad had relatively low toxicity to German cockroaches compared with other insecticides tested in this study. This result further confirmed that the mode of action of spinosad to insects is unique. Fipronil, a relatively new insecticide, was highly toxic to German cockroaches, and the multi-resistance mechanisms in Apyr-R did not confer significant cross-resistance to this compound. Thus, we propose that fipronil could be a valuable tool in integrated resistance management of German cockroaches.

Animals↗
PubMed2001

The molecular interactions of pyrethroid insecticides with insect and mammalian sodium channels.

Recent progress in the cloning of alpha (para) and beta (TipE) Na channel sub-units from Drosophila melanogaster (fruit fly) and Musca domestica (housefly) have facilitated functional expression studies of insect Na channels in Xenopus laevis oocytes, assayed by voltage clamp techniques. The effects of Type I and Type III pyrethroids on the biophysical properties of these channels are critically reviewed. Pyrethroid resistance mutations (termed kdr and super-kdr) that reduce the sensitivity of the insect Na channel to pyrethroids have been identified in a range of insect species. Some of these mutations (e.g. L1014F, M918T and T929I) have been incorporated into the para Na channel of Drosophila, either individually or in combination, to investigate their effects on the sensitivity of this channel to pyrethroids. The kdr mutation (L1014F) shifts the voltage dependence of both activation and steady-state inactivation by approximately 5 mV towards more positive potentials and facilitates Na channel inactivation. Incorporation of the super-kdr mutation (M918T) into the Drosophila Na channel also increases channel inactivation and causes a > 100-fold reduction in deltamethrin sensitivity. These effects are shared by T929I, an alternative mutation that confers super-kdr-like resistance. Parallel studies have been undertaken using the rat IIA Na channel to investigate the molecular basis for the low sensitivity of mammalian brain Na channels to pyrethroids. Rat IIA channels containing the mutation L1014F exhibit a shift in their mid-point potential for Na activation, but their overall sensitivity to permethrin remains similar to that of the wild-type rat channel (i.e. both are 1000-fold less sensitive than the wild-type insect channel). Mammalian neuronal Na channels have an isoleucine rather than a methionine at the position (874) corresponding to the super-kdr (M918) residue of the insect channel. Replacement of the isoleucine of the wild-type rat IIA Na channel with a methionine (I874M) increases deltamethrin sensitivity 100-fold. In this way, studies of wild-type and mutant Na channels of insects and mammals are providing a molecular understanding of kdr and super-kdr resistance in insects, and of the low pyrethroid sensitivity of most mammalian Na channels. They are also giving valuable insights into the binding sites for pyrethroids on these channels.

Animals↗
PubMed2001

Effect of pyrethroids on carbohydrate metabolic pathways in common carp, Cyprinus carpio.

The activity levels of succinate dehydrogenase (SDH) and glucose-6-phosphate dehydrogenase (G6PD) were assessed in various tissues of Cyprinus carpio var communis which had been exposed to lethal concentrations of group-II pyrethroids (deltamethrin, cypermethrin, fenvalerate and fluvalinate) for a period of 72 h. The results indicated a steady decrease in SDH activity with a concomitant increase in G6PD activity. The decreased SDH activity indicated inhibition of SDH at mitochondrial level and the increased G6PD activity an enhancement of an alternative pathway of carbohydrate metabolism, viz the hexose monophosphate shunt (HMP) or pentose phosphate pathway as a biochemical adaptation to overcome the toxic stress.

Animals↗
PubMed2002

Persistence and performance of esfenvalerate residues on broccoli.

The efficacy of esfenvalerate (84 g litre-1 EC; Asana XL) at 7.0 g AI ha-1 on broccoli was tested against the flea beetle, Phyllotreta cruciferae Goeze (Chrysomelidae: Coleoptera) and the imported cabbage worm, Pieris rapae L (Pieridae: Lepidoptera) under field conditions. Insect populations were monitored before and after treatment. Periodic sweep-net collections and examination of the leaves in treated and untreated broccoli plots revealed mean reductions of P cruciferae levels of nearly 98% 1 week post-application compared with untreated plots. The residual toxicity of esfenvalerate was also effective for 2 weeks in reducing population density of P rapae by 69% on broccoli leaves. The impact of esfenvalerate on feeding damage to broccoli leaves was established by counting the number of feeding holes made by P cruciferae on spring broccoli and P rapae on fall broccoli. As the leaf area ingested increased, a linear relationship was seen between the number of holes and number of insects. Results indicated that forage destruction by the two pests was significantly reduced by esfenvalerate application. Esfenvalerate was extracted from broccoli at 1 h and 1, 3, 7, 10, and 14 days post-application for residue analysis. Residues on spring broccoli were 12.2, 5.2 and 2.9 micrograms cm-2 on the leaves and 0.13, 0.05 and 0.02 microgram g-1 on the heads at 1 h, 1 and 3 days, respectively. Only trace levels (0.001 microgram g-1) were detected in/on the heads 14 days after spraying. On the basis of half-life (T1/2) values, persistence of esfenvalerate on spring broccoli leaves (T1/2 = 1 day) was shorter than on fall broccoli (T1/2 = 1.6 days). T1/2 values were 2.1 and 3.6 days on spring and fall broccoli heads, respectively. The implications of these residue levels on re-entry times into treated fields are discussed.

Animals↗
PubMed2002

Fumigant activity of (E)-anethole identified in Illicium verum fruit against Blattella germanica.

The insecticidal activities of materials derived from the fruit of star anise, Illicium verum, against adults of Blattella germanica were examined by direct contact application and fumigation methods, and compared with those of DDVP, deltamethrin and hydramethylnon. The biologically active constituent of the Illicium fruit was characterized as the phenylpropene, (E)-anethole, by spectroscopic analysis. In a filter paper diffusion test with females, (E)-anethole caused 80.3% mortality at 0.159 mg cm-2 at 1 and 3 days after treatment (DAT), whereas 16.7% mortality at 3 DAT was achieved at 0.079 mg cm-2. DDVP and deltamethrin gave > 90% mortality at 0.019 mg cm-2 at 1 DAT. At 0.009 mg cm-2, DDVP and deltamethrin showed 73.3 and 60% mortality at 1 DAT, respectively, but 93.3 and 76.7% mortality at 3 DAT. Hydramethylnon exhibited 0 and 93.3% mortality at 0.159 mg cm-2 at 1 and 3 DAT, respectively, whereas 6.7% mortality at 3 DAT was observed at 0.079 mg cm-2. In a fumigation test with females, (E)-anethole was much more effective in closed cups than in open ones, indicating that the insecticidal activity of the compound was largely attributable to fumigant action. (E)-Anethole and DDVP caused 100% mortality at 0.398 and 0.051 mg cm-2 4 and 1 h after treatment, respectively. (E)-Anethole showed 46.7% mortality at 0.199 mg cm-2 at 3 DAT, whereas deltamethrin and hydramethylnon at 0.796 mg cm-2 was ineffective for 3-day period. As naturally occurring insect-control agents, the I verum fruit-derived materials described could be useful for managing populations of B germanica.

Allylbenzene Derivatives↗
PubMed2002

Susceptibility of house flies (Diptera: Muscidae) exposed to commercial insecticides on painted and unpainted plywood panels.

House flies were collected from dairies in New York state and the levels of resistance to commercially available insecticide formulations were measured on painted and unpainted plywood panels. Dimethoate was ineffective on all surfaces. The wettable powder permethrin formulation was more toxic than the emulsifiable concentrate formulation. The wettable powder cyfluthrin formulation was also more toxic than the recently developed liquid formulation. In general, the best house fly control was obtained on flat latex painted plywood panels and the poorest control on gloss latex painted panels. It is highly unlikely that producers obtain adequate control with dimethoate and permethrin.

Animals↗
PubMed2002

Thermal decomposition and isomerization of cis-permethrin and beta-cypermethrin in the solid phase.

The stability to heart of cis-permethrin and beta-cypermethrin in the solid phase was studied and the decomposition products identified. Samples heated at 210 degrees C in an oven in the dark showed that, in the absence of potassium chlorate (the salt present in smoke-generating formulations of these pyrethroids), cis-permethrin was not isomerized, although in the presence of that salt, decomposition was greater and thermal isomerization occurred. Other salts of the type KXO3 or NaXO3, with X being halogen or nitrogen, also led to a considerable thermal isomerization. Heating the insecticides in solution in the presence of potassium chlorate did not produce isomerization in any of the solvents assayed. Salt-catalysed thermal cis-trans isomerization was also found for other pyrethroids derived from permethrinic or deltamethrinic acid but not for those derived from chrysanthemic acid. The main thermal degradation processes of cis-permethrin and beta-cypermethrin decomposition when potassium chlorate was present were cyclopropane isomerization, ester cleavage and subsequent oxidation of the resulting products. Permethrinic acid, 3-phenoxybenzyle chloride, alcohol, aldehyde and acid were identified in both cases, as well as 3-phenoxybenzyl cyanide from beta-cypermethrin. A similar decomposition pattern occurred after combustion of pyrethroid fumigant formulations.

Chlorates↗
PubMed2002

Cotton whitefly (Bemisia tabaci) resistance to organophosphate and pyrethroid insecticides in Pakistan.

Resistance to three organophosphate and four pyrethroid insecticides was monitored from 1992 to 2000 in field populations of adult whiteflies, Bemisia tabaci, from Pakistan using a leaf-dip method. There was generally a very high resistance to dimethoate and deltamethrin, and a moderate resistance to monocrotophos during 1992 to 1996. From 1997 to 2000, resistance to these insecticides dropped to low levels because of less reliance on them for whitefly control, and introduction of new chemistries with novel modes of action that had no cross-resistance to conventional insecticides. Concurrently, whitefly resistance to acephate, fenpropathrin, lambda-cyhalothrin and bifenthrin mostly remained low. An insecticide resistance management strategy is recommended that particularly emphasizes the rotation of still-effective insecticides from different chemical classes along with the use of novel chemicals and other tactics of integrated pest management.

Animals↗
PubMed2002

Linkage of genes for sodium channel and cytochrome P450 (CYP6B10) in Heliothis virescens.

Genetic linkage of hscp (heliothis sodium channel protein) and CYP6B10 was discovered in Heliothis virescens. The hscp gene encodes the sodium channel target of pyrethroid insecticides and cytochrome P450 genes encode important enzymes involved in detoxication of various pesticides. Previously, two mechanisms, nerve insensitivity due to sodium channel and synergism by propynyl aryl ethers, were observed in pyrethroid-resistant H virescens and were not separated by repeated back-crossing. We hypothesized genetic linkage of target site insensitivity and monooxygenase-mediated detoxication. Single nucleotide polymorphisms were discovered in IIS6 of hscp; Hpy of hscp and CYP6B10. Segregation of these and other markers was tested in backcrosses. We observed cosegregation of hscp to CYP6B10, but both genes assorted independently of y, ye and sex. Genes y and ye assorted independently of each other. This was the first observation of linkage between genes controlling detoxication and sodium ion channel insensitivity in a species known to express high levels of pyrethroid resistance. Linkage was not likely because this species has 31 chromosomes; therefore, we will investigate the possibility of a resistance cassette. We expect similar linkage in other noctuid pests.

Animals↗
PubMed2002

The relative toxicities of insecticides to earthworms of the Pheretima group (Oligochaeta).

An artificial soil test was used to determine the LC50 values of carbaryl, chlorpyrifos, imidacloprid, cyfluthrin and fipronil against earthworms of the Pheretima group. For a 24-h interval, carbaryl was the most toxic to earthworms (LC50 = 77 mg kg-1), followed by imidacloprid (155 mg kg-1), cyfluthrin (351 mg kg-1), chlorpyrifos (390 mg kg-1) and fipronil (> 8550 mg kg-1) as the least toxic. For the 48-h and 7-day intervals, imidacloprid was the most toxic to earthworms (LC50 = 5 mg kg-1 and 3 mg kg-1 respectively), followed by carbaryl (16 mg kg-1; 9 mg kg-1), cyfluthrin (128 mg kg-1; 110 mg kg-1), chlorpyrifos (330 mg kg-1; 180 mg kg-1) and the least toxic was fipronil (> 8550 mg kg-1 both intervals). The surface application rates required to achieve these values are compared with the rates recommended for the control of turfgrass pests.

Animals↗
PubMed2002

Sub-lethal effects of deltamethrin on walking behaviour and response to host kairomone of the egg parasitoid Trissolcus basalis.

The lethal doses of the pyrethroid deltamethrin were estimated for the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae), and the sub-lethal effects of an LD25 on female walking behaviour were evaluated. Linear speed of treated parasitoids was reduced compared with that of untreated ones for a period of up to 24 h. The sub-lethal effects of deltamethrin on parasitoid response to patches contaminated by a contact kairomone from its host, Nezara viridula L (Heteroptera: Pentatomidae), was also evaluated. Both treated and untreated parasitoids responded to host-contaminated patches by increasing residence time and decreasing linear speed. However, treated females showed a significantly lower residence time compared with untreated females. Both treated and untreated females showed a similar decrease over time in the proportion of time spent in the host-contaminated patch. Hence, we hypothesise that the sub-lethal effect of deltamethrin on host foraging may decrease T basalis efficacy in controlling N viridula.

Animals↗
PubMed2002

Group effects on insecticide toxicity in workers of the Formosan subterranean termite, Coptotermes formosanus Shiraki.

Coptotermes formosanus workers were treated topically with insecticide and subsequently held individually or in groups to examine possible effects on insecticide toxicity. Chlorpyrifos, cypermethrin and chlordane toxicities were 1.4-, 1.5-, and 1.3-fold greater, respectively, among workers held in groups compared with those held individually after insecticide treatment. Experiments were conducted to examine how enhanced toxicity occurred among termites held in groups after topical insecticide treatment. When workers were treated topically with chlordane and immediately placed with untreated workers, significantly greater numbers of untreated workers were killed compared with controls at all ratios examined (insecticide-treated:untreated). These data indicated that workers treated topically with insecticide were capable of somehow transferring a lethal dose of insecticide to untreated workers confined in the vial. Chlordane was recovered from untreated workers which had been confined with chlordane-treated workers; significantly higher quantities of chlordane were recovered from dead workers exposed to chlordane-treated workers compared with surviving workers exposed to chlordane-treated workers. Possible mechanisms of insecticide transfer from insecticide-treated to untreated termites are discussed.

Animals↗
PubMed2002

Factors affecting the field performance of an attracticide against the codling moth Cydia pomonella.

Factors affecting the efficacy of an attracticide strategy for the control of the codling moth Cydia pomonella L (Lepidoptera: Tortricidae) were investigated using laboratory and field experiments. The sex-pheromone-based insect-control strategy utilises 100-microliters droplets of a sticky, paste-like formulation containing 1 mg g-1 (E,E)-8,10-dodecadien-1-ol (codlemone) as an attractant for male moths and 40 mg g-1 cyfluthrin, a contact insecticide, applied to branches in the upper parts of the tree crown. The longevity of the treatment under field conditions was assessed in the laboratory by biological testing of variously aged samples of the attracticide formulation which had been applied to the bark of apple trees growing in commercial orchards. Electroantennogram responses of male moth antennae were used to compare codlemone release from the attracticide after different lengths of environmental exposure. Changes in insecticidal efficacy of the same samples were assessed with reference to the speed of knockdown (KT50) and the mortalities after 48 h among populations of male moths confined in cages containing samples of fresh and field-aged formulations. Gradual declines in both the amount of pheromone released and insecticidal activity were observed over the 10-week period of the experiments. Various factors associated with the behaviour of codling moths in the field which might influence the attracticide strategy were also investigated. Although the vertical position of attracticide sources within apple trees had a strong influence on their attractiveness, their horizontal position had none. Results of field trials showed that efficacy of the attracticide depends on the population density of the pest. Under the conditions of the current study a density of three or more sources per tree (= 4500 sources per ha) was required to attain satisfactory levels of codling moth control.

Agriculture↗
PubMed2002

Persistence and leaching of beta-cyfluthrin in alluvial soil of India.

Persistence as affected by rate of application and moisture regimes and leaching of beta-cyfluthrin was studied in alluvial soil under laboratory conditions. The effects of rate of application and moisture regimes on persistence were studied by incubating fortified soil at 0.1, 1.0 and 10.0 mg kg(-1) under air-dry, field capacity and submerged moisture regimes. The initial deposits of 0.09, 1.11 and 10.1 mg kg(-1) dissipated with time and 78.4-100% loss was recorded at 90 days. The half-life values varied from 7.8 to 41.8 days. The rate of dissipation decreased as the rate of application increased under field capacity and submerged conditions. However, under air-dry conditions, the effect was less pronounced, and half-life values showed a reverse trend. Persistence of beta-cyfluthrin under different moisture regimes followed the trend: air-dry > field capacity > submerged. The trend could be attributed to the effect of moisture on number and type of microbes. Leaching was studied in a packed soil column under saturated flow conditions. beta-Cyfluthrin was found to be highly immobile in alluvial soil. No residues were detected in any leachate fraction under the experimental conditions. In column soil, residues were detected at 0-10 cm depth and the major amount (>99%) was recovered from 0-5 cm depth. Although beta-cyfluthrin showed moderate persistence in alluvial soil, the possibility of its leaching to ground water is negligible as a result of its immobility.

Algorithms↗
PubMed2002

Efficacy of the organic-certified insecticide Diatect II against the boll weevil (Anthonomus grandis) in cotton.

The efficacy of the organic insecticide Diatect II against boll weevil (Anthonomus grandis Boheman) in cotton (Gossypium hirsutum L) in the Lower Rio Grande Valley of Texas were assessed in small-plot field trials and greenhouse cage tests using azinphos-methyl treatments as a standard for comparison. Plastic sheets were placed in the furrows of the treated plots to retrieve boll weevils which dropped from the plants after being killed by the insecticides. Samples of live weevils taken by a tractor-mounted vacuum sampler revealed a modest, but significant, reduction in boll weevil populations in Diatect II plots. However, samples of dead weevils indicated that this reduction was due to movement of weevils out of the plots rather than to mortality. This interpretation is supported by greenhouse cage studies, where mortality in Diatect II treated cages was no greater than that in untreated control cages. The effects of insecticide treatments in small plots can be confounded easily and quickly by interplot movement of target insects. Although the relative effects of various compounds can usually be assessed by sampling the populations in plots soon after treatment, the best measure of efficacy is obtained by directly sampling insects that have died in the plot. This parameter is insulated from the effects of interplot movement, unless the toxicant is slow to immobilize the target insect. Taken together, our results indicate little efficacy by Diatect II against boll weevil under our test conditions.

Agriculture↗