Infection of red palm weevil, Rhynchophorus ferrugineus, by spore-forming bacilli indigenous to its natural habitat in Egypt

Abstract

A search for means of biologically controlling the red palm weevil (RPW) Rhynchophorus ferrugineus resulted in the isolation of several microbial cultures belonging to bacteria, actinomycetes and fungi. Among the obtained cultures, three potent spore-forming bacilli were further isolated from natural habitats associated with insect-damaged date palms in Egypt. The isolated bacterial cultures, (strains 73, 15 and 27) were identified as variants of Bacillus sphaericus, B. megaterium and B. laterosporus, respectively. Under standard bioassay conditions, the mortalities of the second-instar larvae of the target insect induced by the three isolated bacilli variants ranged between 40 and 60%. The most active culture (strain no. 73) was identified as B. sphaericus. This isolate formed spherical endospores and crystalline endotoxin comparable to those of B. sphaericus standard strain 2362, which is pathogenic to mosquito larvae, as shown by electron microscopy. However, the amino acid composition of the spore-endotoxin complexes was markedly different.