Naturally existing Beauveria on the surface of stored wheat kernels, and their pathogenicity on Rhyzopertha dominica and Sitophilus oryzae adults

Abstract

Entomopathogenic fungi have been investigated to control stored product pests, as an alternative strategy to chemical insecticides. Although many studies evaluated isolates from various sources, few studies surveyed fungi naturally infecting stored product pests, revealing predominantly Beauveria isolates. This study aimed to reveal the amount of Beauveria carried on the surface of stored wheat kernels, and their pathogenicity against Rhyzopertha dominica and Sitophilus oryzae adults. Sixteen wheat samples from different storage facilities in four cities were examined for existence of Beauveria. One-hundred g of wheat was washed in 100 mL of 2% Tween80 solution. After increasing concentration of possible fungi by centrifugation, the liquid was spread on medium with dodine and monitored at 25±2°C. Nine of the isolates were tested for pathogenicity at 500 ppm (w/w) at 25±2°C, 65±5% r.h. in darkness with five replicates. While only four samples did not have Beauveria, others had 17-2992 cfu/100 g wheat. Six samples had 17-50, four samples 150-858, one sample 1625 and one had 2992 cfu/100 g wheat. Mortalities against R. dominica adults ranged between 5-86% and 32-100% in 7 and 14 days, respectively. Mortality of S. oryzae ranged from 3-45% and 8-83% in 7 and 14 days, respectively. This study demonstrated that wheat kernels can naturally carry Beauveria with various levels of pathogenicity. Potential naturally occurring entomopathogenic fungi can be isolated directly from stored commodities to be evaluated as biological control agents for stored product pest control.

Keywords

• microbial control
• biological control
• entomopathogen
• survey