Natural control of Liriomyza trifolii (Diptera: Agromyzidae) on fresh market green peppers

Abstract

The spatial distribution of Liriomyza trifolii (Burgess) and its associated hymenopterous parasite complex was determined in field grown bell peppers at Weslaco, TX. L. trifolii larvae were most numerous during the first weeks of plant growth on cotyledons and thereafter on mature leaves. After plants reached 75 mm in height (>12 leaves per plant), larvae could be most reliably sampled on mature leaves from the middle 1/3 of the plant. Dispersion indices indicated that L. trifolii larvae were slightly aggregated in the field. Correspondingly, parasitized L. trifolii larvae were randomly distributed within individual plants and amongst plants in the field indicating a random parasite oviposition behavior. L. trifolii larval densities within the field increased slowly during a growing season with some changes in stability of age distribution through time also noted. The loss of leaf area from mining accumulated over time appeared to be the major cause of damage by L. trifolii. Laboratory studies at 24°C showed that mean developmental time from oviposition to adulthood was 20 days. High levels of unexplained mortality occurred in egg and pupal stages. The efficacy of L. trifolii parasites in field grown bell peppers was determined using mechanical exclusion techniques and life table analyses. Parasitism of L. trifolii larvae by seven parasite species was a significant factor in limiting density increases. However, unexplained L. trifolii larval and pupal mortality was equally important. In the absence of parasitism, L. trifolii parasite induced mortality was partially replaced by unexplained larval and pupal mortality. The lack of L. trifolii adult and egg mortality data left questions as to the exact role of all mortality agents. No one mortality factor regulated L. trifolii density in the systems studied.