Influence ofRhopus nigroclavatus(Hymenoptera: Encyrtidae) on the MealybugsTridiscus sporoboliandTrionymussp. (Homoptera: Pseudococcidae)

Abstract

This research investigated parasitism ofthe buffalograss mealybugs Tridiscus sporoboli (Cockerell) and Trionymus sp. by Rhopus nigroclavatus (Ashmead) through rearing and dissection studies, paired comparison tests, and a field survey. Rates ofparasitism reported in this article reflect combined parasitism of the 2 mealybug species. In the rearing study, parasitism of adult female mealybugs by R. nigroclavatus was 48.6%, with an average emergence of 1.77 parasitoids per parasitized mealybug. A maximum of 7 R. nigroclavatus adults emerged from a single mealybug female. Mealybugdissections documented parasitism rates by R. nigroclavatusof78.5, 67.5, and 4.3%, respectively, for adult females, 3rd and 4th (male pupae) instars, and Ist- and 2nd-instar mealybugs. Results revealed the preference of R. nigroclavatusfor adult female mealybugs and later instars, and suggested a potential regulating effect of R. nigroclavatus on buffalograss mealybug populations. Paired comparison tests with and without R. nigroclavatus demonstrated the effectiveness of this parasitoid as a biological control agent for buffalograss mealybugs under greenhouse conditions. Significant differences were detected in the number of nonparasitized mealybugs between treat­ ments containing only mealybugs and treatments containing both mealybugs and parasitoids. Sticky trap captures in the field suggested a functional relationship between the seasonal abundance of R. nigroclavatus and its mealybug hosts.