Potential Use of Local Entomopathogenic Nematodes to ControlBradysia impatiens(Diptera: Sciaridae) Under Laboratory Conditions

Abstract

Bradysia spp. are major pests of undercover crops, to which they can cause considerable economic loss. The use of entomopathogenic nematodes (EPNs) for the control of Bradysia spp. has proven to be relatively advantageous, since sciarids are mostly pests of undercover crops that have a short lifecycle, or for which the application of pesticides is unsuitable. In this study, eight South African local EPN species and a non-native EPN species, namely Steinernema feltiae, were tested for their ability to kill Bradysia impatiens larvae at different temperatures. The results showed four local EPN species, Steinernema yirgalemense, Heterorhabditis noenieputensis, Heterorhabditis indica and Heterorhabditis zealandica, achieving higher than 80 % mortality, at 25 °C and 30 °C, from the different bioassays performed. Heterorhabditis zealandica had the lowest LD50 of 2.60 infective juveniles (IJs) per larva and LD90 of 18.68 IJs/larva. Steinernema yirgalemense had an LD50 of 8.98 and an LD90 of 64.16, which were similar to those of H. indica. Steinernema yirgalemense, H. indica and H. zealandica were all able to reproduce inside the fourth-instar larvae of B. impatiens, and to produce IJs. The relatively larger nematodes, Steinernema jeffreyense, Steinernema khoisanae, and Steinernema litchii were unable to infect the fourth-instar larvae of B. impatiens, which indicated that the size of the EPNs affected their ability to infect fungus gnat larvae. This study demonstrated the high potential for the use of locally isolated EPNs for the control of fungus gnats in South Africa.