Repellent Mechanism Of Metarhizium Spp. Against Bamboo Shoot Wireworms

Wireworms, the larvae of Elateroidea insects, are worldwide subterranean pestscaused huge economic loss. Melanotus cribricollis (Coleoptera:Elateridae) is the dominantand most destructive wireworm of bamboo shoots in southern region of China. Recently,Melanotus cribricollis, occurred extensively and has causing economically severe losses ofbamboo production because of the changes of cultivation techniques and plantation models.Metarhizium spp. is one kind of entomopathogenic fungi which has been proved to beeffective to control subterranean insect pests. In many cases, Metarhizium spp. caused highlevels of wireworm motality in laboratory, but population control from field release wereoften less effective. The repellency of Metarhizium spp. against wireworms was suspectedthe main reason. In order to demonstrate the repellent effect and understand the chemicalmechanism of Metarhizium spp. against wireworm, we used laboratory experiments toexamine the repellent effect of the conidium、volatile organic compounds and non-volatileorganic compounds of Metarhizium pingshaense WP08on the behaviour of Melanotuscribricollis wireworm in present study. The results are summarized as follows:(1) The repellency of Metarhizium pingshaense WP08conidium with differentconcentrations were studied, the results showed that only when the concentration was5×108spore/g dry soil, repellent effect was significant,71.77%wireworms tended to stayin the soil treated with deinoized water, and28.23%wireworms chose the soil treated withconidium. However when the concentration was5×107or5×106spore/g dry soil, there wasno repellency of conidium, wireworms even had the tendency toward the conidiumtreatment,60.38%wireworms chose the conidium soil, higher than39.62%wirewormschose the ck treatment.(2) According to the result of Metarhizium pingshaense fermentation repellency test,77.01%wireworms preferred the side treated with deinoized wanter, and22.99%wireworms chose the other side treated with fungi fermentation, Metarhizium pingshaensefermentation has significant repellency to Melanotus cribricollis wireworms.(3) In Y-tube olfactory test to analysis the repellent feature of Metarhiziumpingshaense volatiles,51.83%wireworms preferred to the volatiles emitted form thePPDA culture medium, and48.17%chose to the volatiles emitted from Metarhiziumpingshaense cultivation, there was no significant difference between the two treatments.The volatile emitted form Metarhizium pingshaense cultivation was not repellent toMelanotus cribricollis wireworms. (4) More than30compounds emitted form three isolates of Metarhizium spp.weretentatively identified by headspace solid phase micro-extraction (HS-SPME) coupled withGC-MS. The compounds included hydrocarbons, oxycompounds, alkenes, alcohols andketones. Both qualitative and quantitative differences of volatiles were affected by fungiisolates, growth period and culture medium.For the first time, this study demonstrated the conidium and the fermentation ofMetarhizium pingshaense was repellent to Melanotus cribricollis wireworms, but theVOCs emitted from Metarhizium pingshaense showed no significant repellency. Howeveronly when the conidium concentration was high enough in the soil（eg.5×108spore/g drysoil）, the repellent effect was significant. These results have provided important basicinformation of chemical mechanism of fungi-repellency and are helpful for effectivedeployments of metabolites derived from entomogenous fungi in behavioral manipulationof insect pests.