Parasitism of Eggs of the Australian Plague Locust Chortoicetes terminifera (Walker) (Orthoptera: Acrididae) by Scelio fulgidus Crawford (Hymenoptera: Scelionidae)

Abstract

In eastern Australia, parasitism of eggs of the Australian plague locust, Chortoicetesterminifera (Walker) by the wasp Scelio fulgidus Crawford was surveyed between 1975 and 1994. In the arid interior, where most plagues of C. terminifera originate, parasitism was moderate to high (15-45% of eggpods), yet locusts increased to plague proportions in spite of parasitism. The consistently moderate parasitism of C. terminifera in the interior, in spite of its low rainfall, is a result of S. fulgidus development being well synchronized with that of its host. *After several generations in the interior, C. terminifera typically migrated from the interior to sub-coastal agricultural areas. When locusts invaded agricultural areas during summer, parasitism was only slightly lower than that in the interior, though parasitism declined between summer and autumn. Often the locust population in agricultural areas collapsed before the next summer and parasitism was very high in the eggpods of remnant locusts. The high post-outbreak parasitism levels were not reached during 1990-94, when a preventative control program kept locust populations from reaching plague proportions: lower host numbers mean a lower absolute abundance of S. fulgidus, so that when host populations collapsed, the parasitism in residual locust populations increased less. [