Pathogenicity Of Four Entomopathogenic Nematodes Toward Red Imported Fire Ant And Combined Effects With Pesticides

Red imported fire ant(Solenopsis invicta Buren)is a notorious invasive pest,which has had the substantial impact on wildlife,humans,and agriculture with economic costs.Chemical pesticides(toxic baits and contact insecticides)used to control red imported fire ant lead to environmental pollution,pesticide residues.The development of new technologies utilizing multiple strategies,such as biological control agents and biopesticides,which used to disrupt colony organization were needed for the future management of S.invicta.Entomopathogenic nematodes(EPNs),a kind of biological agents,has been widely used to control soil pest with its advantages of special host,wide host range,safety of human and animal.To screening the advantage of entomopathogenic nematodes strain to control red imported fire ants,four entomopathogenic nematodes respectively with a low toxicity pesticides,two experiments were tested.The results are showed as follows:1.Four entomopathogenic nematodes at 1×10~4 IJs/ml concentration,Steinernema carpocapsae All,Steinernema feltiae SN,Steinernema longicaudum X-7,Heterorhabditis bacteiophora H06 were tested to different developing stages and classes of red imported fire ant(egg,larvae,pupae,worker and alate).The results showed that all of four nematodes worms had a mortality of more than 80%in 24 hours,and that Steinernema longicaudum X-7 and Heterorhabditis bacteiophora H06 had a mortality of 100%in eggs.The mortality of Steinernema carpocapsae All and Steinernema feltiae SN against red imported fire ant larvae reached more than 80%.Steinernema longicaudum X-7,Steinernema carpocapsae All and Steinernema feltiae SN had a positive mortality of 100%,97%,and 84%against red fire ant pupae.The single nematode had less effect on ant works and reproductive insects.2.A single nematode used alone to the red imported fire ants show that the nematode Steinernema longicaudum X-7 and Heterorhabditis bacteiophora H06 at high concentration of 4×10~4 IJs/ml,the mortality of the red imported fire ants from the fifth day is significantly higher than other processing.Compared with the other three nematode worms,the nematode Steinernema feltiae SN has the highest fatality rate for red imported fire ant workers.At the highest concentration of 4×10~4 IJs/ml,the fatality rate of red fire ant worker ants on day 10 was 58%.Therefore,we screened out Steinernema feltiae SN insect pathogen nematodes for further study on red fire ant worker ants.3.Steinernema feltiae SN was applied to tested on worker by 7 difference concentrations.The results showed that the nematode caused mortality of fire ant worker was decreased when the concentration was higher than 4×10~4 IJs/ml.To determine whether the existence of the workers will influence the mortality of fire ant caused by entomopathogenic nematodes Steinernema feltiae SN fire ant egg,larva,pupa with or without worker were tested.The results show that the existence of the workers will increase the mortalities of fire ant egg,larva,pupa.Moreover,the higher the number of worker ants,the higher the mortality of eggs,larvae and pupae of red fire ants caused by Steinernema feltiae SN.4.Three candidate synergists,a low-toxicity insecticides(β-cypemethrin)and two biopesticides(sophocarpidine,metarhizium anisopliae),were tested to the survival rate of the entomopathogenic nematode.Results showed that three candidate at high concentration(sophocarpidine at 6.66μg/ml,β-cypemethrin at 0.117μg/ml,metarhizium anisopliae at10×10~6 spore/ml)had no harm to the nematode,and did not have high lethal effect(<66%)to the red imported fire ant.5.The combined effects of different concentrations of Steinernema feltiae SN nematodes with sophocarpidine,β-cypemethrin and metarhizium anisopliae against worker of red imported fire ant were determined.The results showed that:compared to using the Steinernema feltiae SN or sophocarpidine,a mixture of Steinernema feltiae SN nematodes and sophocarpidine(6.66μg/ml)against to the worker,the control effect was increased by1.65 times,1.39 times,respectively.After Steinernema feltiae SN nematodes were mixed withβ-cypemethrin(0.117μg/ml),the control effect was 1.81 times,1.37 times,which showed a synergistic effect.Steinernema feltia SN nematode and metarhizium anisopliae spores(10×10~6 spores/ml)mixture,the control effect is increased by 1.36 times and 1.58times to using Steinernema feltiae SN or metarhizium anisopliae alone.All of the mixture treatments were showed synergistic effect.Especially,Steinernema feltiae SN with metarhizium anisopliae spores(10×10~6 spores/ml)mixture control effect is as high as 90% above.