A New Formulation Of Wettable Powder Of Beauveria Bassiana For Plutella Xylostellu Control

A migratory pest, the diamondback moth, Plutella xylostella, is one of the mostserious cruciferous vegetables pests, which infests more than40different cruciferousvegetables. It has developed high resistance to almost all insecticides, even including Bt,and needs biological alternatives.In the present study, through comparison of sporulation on66isolates of Beauveriabassiana from lepidopteran insects,29were chosen for bioassay on the diamondback moth.Bb2390, a highly virulent isolate, was chosen for its highest virulence to the second-instarlarvae, with LC50value on the7nd d at1.56x105, and LT50value at4.61d under theconcentration of1.0x107conidia·mL-1. PXBB, a wettable powder （WP） was developedbased on Bb2390for the diamondback moth control. The results showed that the isolateinfected all stages of P. xylostella, causing37.2%mortality of the eggs,90.3%mortality ofthe second-instar larvae,58.8%mortality of the pupae, and24.5%mortality of the adults.In the present study, conidia produced through the solid-liquid fermentation process,were tested for their quality indicators, with1.18±0.13×10¹¹conidia·g^-1, a germination rateof97.34±1.20%, moisture content of1.58±0.06%. Screening a WP formulation, the typesand amount of carrier, wetting agent, dispersant and protectant were determined with theone by one screening method, and quality index was evaluated according to the nationalstandard.7kinds of vectors were determined for the wetting time, suspension rate andbiocompatibility,5kinds of wetting agent and4kinds of dispersant were determined tocompounded test for the wetting time, suspension rate and biocompatibility, some kinds ofprotectant were tested for the protection performance and biocompatibility. The optimalformulation were as follows: the content conidium of Bb2390, dispersing agent B, wettingagent A, UV protection agent C, and so on, filler diatomite were10.0%,4.5%,3.0%,0.5%and so on, respectively. The storage results of PXBB showed that the germination rate ofthe spores declined slowly both at4℃and at25℃within the13months of storage, whilethe lower temperatured benefited the storage. Stored at4℃, the germination rate of sporesand PXBB both remained more than80%on the13thmonth, respectively. Compered withthose refrigerated at4℃, the germination rate of spores and PXBB both declinedenhancedly at25℃, which of spores declined sharply in the4^thmonth, and droped to48.37%in7months, and finally no germination within2.42%was found in13^thmonthstorage. However, compared with the spores at25℃, the decrease of germination of PXBBstorage at25℃started obviously on the5thmonth, declined to70.67%,60.7%and49.92%, on the8^th,10^thand12^thmonth, respectively. Spores in a room declined very sharply, andfinally no germination was found in8^thmonth.In plot tests, the field efficacy of WP containing108conidia·mL^-1against the2^ndinstars of P. xylostella was at65.12%, while a water suspension with0.1%Tween-80at46.51%.