Interactions of Undescribed Drilus Beetle Larvae with Pestiferous Limicolaria flammea (Gastropoda: Achatinidae): Are There Prospects for Biocontrol?

Abstract

The garden snail, Limicolaria flammea is a seasonal pest of several horticultural crops in most of the agroecological areas in Nigeria. The level of damage to crops is especially enormous in the South because of its ability to feed on different crops and the timing of abundance, the early rain season, which usually coincide with onset of rain-fed crop production which expose seedlings and grown-up crop plants to serious damage. In this study, we recorded occurrence data of Limicolaria flammea in okra, carrot, sweet potato, lettuce and maize within a single multi-crop organic farm in order to understand its food preference. Activities of the predatory beetle larvae, Drilus sp was observed within the environment. The appearance of the larvae was described and its interaction with L. flammea was studied to generate some data on the proportions of snail mortality caused by Drilus sp and other mortality factors that naturally regulate the population dynamics of L. flammea within the environment. There was no statistically significant difference in the average number of snails recorded in the different cropping fields [F (4,15) =1.369, P=0.291]. The activities of Drilus larvae against L. flammea was higher in okra and carrot plots as snail mortality due to the larvae attack were significantly higher compared to what was recorded in other crop plots [F (4, 30) =3.998, P=0.01].The Drilus larvae predate on L. flammea by appertural entry, biting through the soft tissues around the mantle to gain entrance and moult into instar larvae within the snail shell in 15-20 days, leaving its exuviae behind in the shell in all the specimens observed (n=40). The Drilus species being reported in this study is morphologically distinct from other described species in available literature. The study suggested that the Drilus species is less known and there are potentials that the species could be useful in inundative biocontrol approaches for the management of pestiferous gastropod populations.