Laboratory studies on the biology of Orgilus jenniae (Hymenoptera: Braconidae), a parasitoid of the potato tuberworm, Phthotimaea operculetta (Lepidoptera: Gelechiidae)

Abstract

The behaviour, host relationships, egg, larval and pupal morphology and population growth potential of Orgilus jennieae Marsh, an exotic parasite of the potato pest Phthorimaea operculella (Zell.) from Costa Rica, were studied in the laboratory in California, and the results were compared with those of similar studies on the exotic species O. lepidus Mues. from Argentina and O. parcus Turner from South Africa. All 3 speies have been introduced into California but have failed to become established. O. jennieae usually parasitised 1st- or 2nd-instar larvae on potato foliage. In tubers, parasitism became increasingly difficult with increasing host age, since host larvae having made long mines were out of reach of the ovipositor of O. jennieae unless they produced a secondary exit hole; the 2nd instar appeared to be the best host age for parasitism at a density of 125 host larvae/tuber. At 24-26øC, 40-50% RH and 12 h photoperiod, fecundity averaged 375.2 eggs/female in tubers and 436 on foliage, and females developing in hosts on foliage and tubers lived for 25.5 and 16.9 days, respectively. Parasitisation of Phthorimaea larvae on potato foliage permitted greater and more rapid population increases of O. jennieae than did parasitisation in tubers. The population growth potential of the parasite was at least equal to that of P. operculella in tubers and much higher on foliage.