Control of Root Gnats (Sciaridae: Diptera) by Tetradonema plicans Hungerford (Tetradonematidae: Nematoda) Produced by a Novel Culture Method

Abstract

A survey of adult sciarid root gnats in greenhouses at the University of California, Riverside, demonstrated that 9.0% were infected with Tetradonema plicans. The mean number of gravid T. plicans females per infected sciarid adult was 5.1 with a range of 1 to 48 parasites per host fly. Only 1.4% of the maggots collected from pots in the greenhouses were infected. To study the bionomics of T. plicans a simple system for culturing sciarid flies and T. plicans and extraction of T. plicans eggs was developed. Fermented sphagnum moss and cellulose (4:1) with rabbit chow was the basic culture medium. Up to 3 × 10 9 T. plicans eggs were produced from an inoculum of 6 × 10 4 eggs per culture container. Eggs were collected by seiving or sucrose flotation. Infections in 1-liter containers showed that T. plicans (10 T. plicans eggs per sciarid larva) reduced sciarid fly populations by 74 to 80% for 4 months. Steinernema carpocapsae had no effect on sciarid flies, but in contrast, Heterorhabditis bacteriophora (10 juvenile nematodes per host larva) decreased sciarid populations by 60%. At 100-fold higher infection level all sciarid larvae were killed, but H. bacteriophora was unable to reproduce in the sciarid larvae.