Histopathologic Research Of Locusta Migratoria Manilensis Meyen Infected By Metarhizium Acridum Through Oral Feeding

Metarhizium acridum IMI330189has higher pathogenicity to locust and grasshopper. Filedapplication of Metarhizium bait and oil formulation gets higher control effect. But it is a controversialtopic that whether Metarhizium can infect insects through the digestive tract. Different ways ofinoculation and paraffin sectioning were used to study the infection process of M.acridum on Locustamigratoria manilensis Meyen.Pathogenicity of M. acridum IMI330189to3rd instars larvae of locust with two differentinoculation ways was measured under the same spore quantity (3×107each locust). The result indicatedthat bait exhibited higher virulence to locust than spray treatment. Food consumption of locust fed on M.acridum bait was significantly decreased in24h, which is negative correlated with the sporeconcentration. Pathological change showed that M. acridum can destroy the integrity of midgut. After2days of bait eating, peritrophic membrane of the midgut disappeared, microvillus exfoliated in3days.Hypha bodies were not observed in tissues of live treatments. The hyphal growth was generalized in thebody cavity of the cadaver, but was never observed in the lumen of the gut until2d post-mortem.Locust saliva and fecal pallets inhibited spore germination of M. acridum, there is a negativecorrelation between inhibition and dilution ratio of two above materials：1) The spore germination ratewas under30%when mixed with10%saliva. There was no spore germination when the mixed salivaconcentration was above20%. The spore germination rate recovered after saliva washed away but cannot go back to the original level. Spore germination rate is30%to40%when treated with100%saliva.The results indicated that locust saliva can inhibited parts of M. Acridum spores.2) Spore germinationrate reduced to60%when the mixed fecal pallets concentration was up to20%, but the germination raterecovered considerably when spores separated from locust fecal pallets. The results indicated that theinhibition of locust fecal pallets can released when being washed.The results showed that the hyphal bodies appeared to be more common around the mouthparts,decreasing in concentration in tissues of thorax and abdomen. Slices of the mouthparts and body surfaceshowed that bait has two main invasion parts: penetration through the mouthparts and body surface.