Action of Bracon hebetor1 Say as a Parasite of Plodia interpunctella2 at Controlled Densities3

Abstract

Under controlled conditions of 27°C and 60% relative humidity, standard populations of about 1800 larvae of the Indian meal moth, Plodia inter punctella (Hübner), were allowed to proceed through 12 days of larval development. Adults of the braconid parasite Bracon hebetor Say were then introduced at 9 different densities and with a sex ratio of 2 ♀ : 1 ♂. Tests at each density were replicated and randomized, and each experiment was terminated before the initiation of a 2nd host generation. Equilibrium was not sought, but rather the optimum ratio of parasite:host density for most efficient immediate control of the host. At an introduction of 250 ♀ Bracon, 97% of Plodia larvae were killed. Higher numbers of female Bracon up to 1000 did not increase this mortality significantly. The sex ratio of surviving Plodia in a parasitized colony was found to be dependent on the density of female Bracon. A significantly larger number of female larvae were parasitized in preference to male. The sex ratio of Bracon in the F1 generation appeared also to vary with the host:parasite density ratio. The female:male ratio of F1 Bracon showed a quadratic relationship, with a maximum number of female F1 at the 250-♀ wasp density.