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

In Eupelmus orientalis and Dinarmus basalis, two ectoparasitoid species of Callosobruchus maculatus larvae, pre-imaginal development occurs within a l eguminous seed, and is then impossible to observe directly. Offspring sex r atio is normally determined when adults emerge, and mortality during pre-im aginal stages remains unknown. By using translucent gelatine capsules conta ining a host larva to mimic the seed, we conducted an experimental study of offspring production and sex ratio with measurements of growth and pre-ima ginal mortality. Mated females were allowed to lay eggs on hosts in seeds o r in gelatine capsules. In the gelatine capsules the parasitoid was observe d daily and measured to assess if the offspring sex ratio can be determined before emergence of adults. When seeds are replaced with gelatine caps, th e 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 orien talis (egg numbers constant, sex ratio diminishing from 0.75 to 0.46) and q uantitatively in Dinarmus basalis (egg numbers diminishing, sex ratio maint ained about 0.7). In Eupelmus orientalis, pre-imaginal mortality occurs pri ncipally in the first three days, the critical stage is hatching, and the f inal 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 b ut only after most mortality has occurred.