Host selection and strain occurrence in Apanteles flavipes (Cameron) (Hymenoptera: Braconidae) and its bearing on biological control of graminaceous stem-borers (Lepidoptera: Pyralidae)

Abstract

Females of the Pakistan strain of Apanteles flavipes (Cam.) (which originates from Japan and is maintained on larvae of Chilo partellus (Swinh.) reared on maize) were readily attracted to maize stems but not to sugar-cane stems in the laboratory. Ovipositor probing occurred in the presence of unwashed host larvae, particularly of C. partellus and/or frass from host larvae fed on maize. Ovipositor probing did not occur in the presence of dried frass, dried frass that had been remoistened with water or frass from C. partellus fed on a diet of gram (Cicer arietinum) flour. The Pakistan strain of A. flavipes is morphologically identical to a strain of A. flavipes imported from India into Florida and established on Diatraea saccharalis (F.) fed on a soyabean flour-wheat germ diet. Reciprocal crosses between the two strains (Pakistan and USA) and between the F₁, adults produced both male and female progeny. Nevertheless, behavioural differences between the strains were found in laboratory tests in that the USA strain responded more strongly to larvae of Acigona steniellus (Hmps.) fed on sugar-cane, was more attracted to sugar-cane stalks than to maize stalks and was not encapsulated by D. saccharalis larvae, whereas at least one-fifth of the Pakistan strain larvae were encapsulated. The existence of different strains of Apanteles flavipes adapted to different graminaceous crops suggests that parasite plant preference as well as host preference and suitability must be considered during attempts to introduce exotic parasites. It is recommended that A. flavipes strains adapted to sugar-cane be introduced into Pakistan for establishment on stem-borers of sugar“-cane.