Studies On Toxicity Of Insecticides (Acaricides) To Amblyseius Barkeri And Sublethal Effects

Amblyseius barkeri is a common natural enemy in citrus orchard and it plays an important role in control ofPanonychus citri McGregor.The study on the susceptibility of Amblyseius barkeri to 11 insecticides,effects of sublethal doses(LC₂₀ of pyridaben,abamectin and fenpropathrin,LC₂₀,LC₃₀ and LC₄₀ of pyridaben ) on predation of Amblyseius barkeri,influence of sublethal doses of pyridaben on population dynamics and GSTs of Amblyseius barkeri were conducted at the laboratory. The major results are as follows:1 Toxicity of 11 insecticides to Amblyseius barkeriToxicity of pyridaben and ten other insecticides to Amblyseius barkeri was determined using leaf residue method in the laboratory.The results showed that fenpropatbrin of pyrethroid pesticide had the highest toxicity to Amblyseius barkeri with LC₅₀ 0.3923 mg/L.Organophosphorus insecticides had the higher toxicity.And abamectin was safe to adult,with LC₅₀ 173.6564 mg/L.The order of toxicities of the 11 pesticides from high to low against the adult females of Amblyseius barkeri was fenpropathrin > phoxim > guosheng(Tobacco,Matrine) > parathion > malathion > omethoate > emamectin benzoate > isocarbophos > dicofol> pyridaben > abamectin.2 Assessment of the impact of abamectin,pyridaben and fenpropathrin on Amblyseius barkeriLeaf disc bioassay was employed in the laboratory to investigate the effect of sublethal doses of selected pesticides,including abamectin,pyridaben and fenpropathrin,on the functional response of Amblyseius barkeri in preaying the Panonychus citri.Results revealed that,fenpropathrin showed a rather strong influence on the predation function of Amblyseius barkeri in contrast to abamectin and pyridaben.Except some changes of the parameters e.g,the functional response model of Amblyseius barkeri preaying on the Panonychus citri were all conformed to Holling's typeâ…¡curve in spite of pretreated with sublethal doses of these insecticides.The maximal predatory capacities of Amblyseius barkeri that pretreated by the three sublethal of pesticides were reduced.They were changed with prolonged handing time,declined predatory rates and the searching efficiencies than untreated.The E-values of fenpropathrin were severer than the other pesticides,and the fecundity of Amblyseius barkeri was significantly influenced.Therefore,abamectin was a relatively safe pesticide to Amblyseius barkeri and its affects were small to lethality and predation function. 3 Influence of sublethal doses of pyridaben on the function response of Amblyseius barkeri prisoner to Panonychus citriInfluence of the sublethal dose treatment of pyridaben to predatory response of Amblyseius barkeri was studied.The results showed that there were some changes in the parameters of the model and the predatory capacities and the searching capability of Amblyseius barkeri that pretreated by sublethal dose were significantly reduced.The predatory capacities of AmbIyseius barkeri were obviously enhanced when we treated the panonychus citri with sublethal dose.4 Impact of sublethal doses of pyridaben on experimental population of Amblyseius barkeriThe lifetable method was employed under the suitable comprehensive laboratory conditions to study the development and the fecundity of experimental population of Amblyseius barkeri treated by sulethal doses of pyridaben on.The results revealed that there were no significant difference in the life span and the fecundity per female between the treated population and the control.The growth duration of the larve and the total were lengthened after the mites in the nymph were treated with pyridaben.LC30 had obviously stimulated effects on the fecundity per femal,the fecundity per female per day and prolonged oviposition period.The parameters of the laboratory population were different in all treatments,namely intrinsic rate of increase(r_m) and finite rate of increase(2) decreased while the average generation time(T) and population double time(t) increased under the effects of the pesticide.The treatment at LC₄₀ could significantly decrease r_m,Rn andλ,so pyridaben may interfere with the F₁ of Amblyseius barkeri and population growth rate.5 Effects of sublethal doses of pyridaben on the specific activity in Amblyseius barkeriThe effects of sublethal doses of pyridaben on GSTs of Amblyseius barkeri were studied using microplate reader.The specific activity of GSTs of the Amblyseius barkeri were all increased while that of treated by LC₄₀ showed significant change after treated with sublethal doses about 24 hours. On the kinetic study,we found that the K_m value of GSTs decreased indistinctively in Amblyseius barkeri treated with pyridaben compared with that of the control.The GSTs activities were changed with time by LC₂₀ of pyridaben and had an obvious time effect.