Egg‐laying, pre‐imaginal growth dynamics, and mortality in Eupelmus orientalis and Dinarmus basalis, two solitary ectoparasitoids of Callosobruchus maculatus

Abstract

AbstractIn Eupelmus orientalis and Dinarmus basalis, two ectoparasitoid species of Callosobruchus maculatus larvae, pre‐imaginal development occurs within a leguminous seed, and is then impossible to observe directly. Offspring sex ratio is normally determined when adults emerge, and mortality during pre‐imaginal stages remains unknown. By using translucent gelatine capsules containing a host larva to mimic the seed, we conducted an experimental study of offspring production and sex ratio with measurements of growth and pre‐imaginal mortality. Mated females were allowed to lay eggs on hosts in seeds or in gelatine capsules. In the gelatine capsules the parasitoid was observed daily and measured to assess if the offspring sex ratio can be determined before emergence of adults. When seeds are replaced with gelatine caps, the number of egg‐laying females decreases (48% in Eupelmus orientalis and 72% in Dinarmus basalis of females ovipositing on seeds lay eggs on gelatine capsules), and the offspring output changes qualitatively in Eupelmus orientalis (egg numbers constant, sex ratio diminishing from 0.75 to 0.46) and quantitatively in Dinarmus basalis (egg numbers diminishing, sex ratio maintained about 0.7). In Eupelmus orientalis, pre‐imaginal mortality occurs principally in the first three days, the critical stage is hatching, and the final mortality is 30.1%. In Dinarmus basalis, mortality of larvae increases gradually from the 2nd to the 7th day, the final mortality being 13.6%. (3) In both species sex of the offspring can be determined before emergence but only after most mortality has occurred.