Effects of Growing Medium Type and Predator:Prey Ratio on Rove Beetle, Dalotia coriaria (Coleoptera: Staphylinidae), Adult Predation on Fungus Gnat, Bradysia sp. nr. coprophila (Diptera: Sciaridae), Larvae

Abstract

Fungus gnats, Bradysia spp. (Diptera: Sciaridae), are major insect pests because the larvae can directly damage plants grown in greenhouse production systems. In general, insecticides are commonly used to suppress fungus gnat larval populations. However, the rove beetle, Dalotia coriaria (Kraatz) (Coleoptera: Staphylinidae), a commercially available predator of insect pests, including fungus gnat larvae, may be an alternative to using insecticides. Growing medium selection used for growing plants can influence insect pest and predator interactions in greenhouse production systems; however, quantitative information is limited. Therefore, we conducted greenhouse experiments and a laboratory experiment to determine the effects of growing medium type on D. coriaria adult predation and fungus gnat, Bradysia. sp. nr. coprophila (Lintner) (Diptera: Sciaridae), larval survival when feeding on the roots of coleus, Solenostemon scutellarioides (L.) Codd, plants. In addition, experiments were conducted to determine the number of rove beetle adults, based on predator:prey ratios, needed to regulate fungus gnat larval populations. In all three experiments, fewer fungus gnat larvae survived in Pro-Mix BX than the Berger BM1 growing medium, and rove beetles reduced the number of fungus gnat larvae in both growing media in the greenhouse experiments. Although predator:prey ratio was not significant, we found that 10 rove beetle adults per 15.2-cm diameter container (1834.82 cm3 with 2.0 L of growing medium) regulated fungus gnat larval populations at the densities investigated. Therefore, greenhouse producers should consider the effects of production practices, such as growing medium type, when using rove beetles to regulate fungus gnat larval populations.