azadirachtin and cypermethrin

Oedaleus asiaticus (Bey-Bienko) is an economically devastating locust species found in grassland and pastoral areas of the Inner Mongolia region of northern China. In this study, resistance to three frequently used insecticides (beta-cypermethrin, matrine, and azadirachtin) was investigated in six field populations of O. asiaticus using the leaf-dip bioassay method. The inhibitory effects of synergists and the activities of detoxification enzyme activities in the different populations were determined to explore potential biochemical resistance mechanisms. The results showed that the field populations SB (resistance ratio [RR] = 7.85), ZB (RR = 5.64), and DB (RR = 6.75) had developed low levels of resistance to beta-cypermethrin compared with a susceptible control strain. Both the SB (RR = 5.92) and XC (RR = 6.38) populations had also developed low levels of resistance against matrine, with the other populations remaining susceptible to both beta-cypermethrin and matrine. All field populations were susceptible to azadirachtin. Synergism analysis showed that triphenyl phosphate (TPP) and diethyl-maleate (DEM) increased the toxicity of beta-cypermethrin significantly in the SB population, while the synergistic effects of TPP, piperonyl butoxide (PBO), and DEM on the toxicity of matrine were higher in SB (SR 3.86, 4.18, and 3.07, respectively) than in SS (SR 2.24, 2.86, and 2.29, respectively), but no synergistic effects of TPP, PBO, and DEM on azadirachtin were found. Biochemical assays showed that the activities of carboxylesterases (CarEs) and glutathione-S-transferases (GSTs) were significantly raised in all field populations of O. asiaticus, with a significant positive correlation observed between beta-cypermethrin resistance and CarE activity. The activities of cytochrome P450 monooxygenases (P450) and multi-function oxidases (MFO) were elevated in all six field populations, and P450 activity displayed strong positive correlations with the three insecticides. Our findings suggest that resistance to beta-cypermethrin in O. asiaticus may be mainly attributed to elevated CarE and GST activities, while P450 plays an important role in metabolizing matrine and azadirachtin. Our study provides insights that will help improve insecticide resistance management strategies.

Topics: Animals; China; Grasshoppers; Insecticide Resistance; Insecticides; Matrines; Pyrethrins

Intensive agriculture has resulted in an indiscriminate use of pesticides, which demands in-depth analysis of their impact on indigenous rhizospheric microbial community structure and function. Hence, the objective of the present work was to study the impact of two chemical pesticides (chlorpyrifos and cypermethrin) and one biological pesticide (azadirachtin) at two dosages on the microbial community structure using cultivation-dependent approach and on rhizospheric bacterial communities involved in nitrogen cycle in Vigna radiata rhizosphere through cultivation-independent technique of real-time PCR. Cultivation-dependent study highlighted the adverse effects of both chemical pesticide and biopesticide on rhizospheric bacterial and fungal communities at different plant growth stages. Also, an adverse effect on number of genes and transcripts of nifH (nitrogen fixation); amoA (nitrification); and narG, nirK, and nirS (denitrification) was observed. The results from the present study highlighted two points, firstly that nontarget effects of pesticides are significantly detrimental to soil microflora, and despite being of biological origin, azadirachtin exerted negative impact on rhizospheric microbial community of V. radiata behaving similar to chemical pesticides. Hence, such nontarget effects of chemical pesticide and biopesticide in plants' rhizosphere, which bring out the larger picture in terms of their ecotoxicological effect, demand a proper risk assessment before application of pesticides as agricultural amendments.

Topics: Chlorpyrifos; Denitrification; Fabaceae; Gene Expression Regulation, Bacterial; Genes, Bacterial; Limonins; Nitrification; Nitrogen Fixation; Pesticides; Pyrethrins; Rhizosphere; Soil Microbiology

Habrobracon hebetor Say is an ectoparasitoid of larval stage of various lepidopteran pests. Lethal and sublethal effects of azadirachtin and cypermethrin were evaluated on adult and preimaginal stages of H. hebetor under laboratory conditions. Contact exposure bioassays with adults indicated that the lethal concentration (LC50) of two commercial azadirachtin-containing formulations, NeemGuard and BioNeem, were 43.5 and 10.2 microg a.i./ml, respectively. The LC50 of cypermethrin was 5.4 microg a.i./ml. When larval stage of H. hebetor was exposed to these insecticides with a field recommended concentration of NeemGuard, BioNeem, or cypermethrin by a dip protocol, the emergence rate was reduced by 39.0, 36.6, and 97.6%, respectively. To assay the sublethal effects of these insecticides, adult wasps were exposed to an LC30 concentration of the insecticides, and then demographic parameters of the surviving wasps were determined. Fecundity, fertility, and parameters including the intrinsic rate of increase (r(m)) were affected negatively. The r(m) values following exposure to NeemGuard, BioNeem, cypermethrin, or mock treatment were 0.143, 0.149, 0.160, and 0.179, respectively, female offspring per female per day, respectively. The current study showed that cypermethrin had more acute toxicity on larval and adult stages of H. hebetor compared with azadirachin. The commercial formulations of azadirachtin and cypermethrin negatively affected most of the life table parameters of the parasitoid. Semifield and field studies are needed for obtaining more applicable results on combining H. hebetor and the tested insecticides for an integrated pest management-based strategy for crop protection.

Topics: Animals; Female; Insecticides; Larva; Life Tables; Limonins; Male; Pyrethrins; Random Allocation; Wasps

Topics: Abdomen; Animals; Chemoreceptor Cells; Insecticides; Interneurons; Limonins; Male; Periplaneta; Pyrethrins; Triterpenes