Effect of three entomopathogenic nematode species to Trogoderma granarium Everts (Coleoptera: Dermestidae) larvae on stored-wheat

Abstract

Grain commodities are subjected to multiple insect infestations during processing and storage. The kharpa beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) is categorized as a destructive stored-product pest due to its elevated survival potential, preference for dry conditions and resistance to many insecticides. While public concern about pesticide related risks increases, the development of alternative, environmentally more benign disinfestation methods of stored commodities is pursued. The current study evaluated the effectiveness of three entomopathogenic nematodes, Heterorhabditis bacteriophora Poinar (Rhabditita: Heterorhabditidae), Steinernema carpocapsae (Weiser) (Rhabditita: Steinernematidae) and Steinernema feltiae (Filipjev) (Rhabditita: Steinernematidae) against small and large larvae of T. granarium. Suspensions of nematodes were applied at six doses: 100, 500, 1000, 5000, 10000 and 50000 infective juveniles (IJs)/ml of water on wheat at 30 °C. Mortality of larvae was estimated 4 and 8 days post-exposure to nematodes. All three entomopathogenic nematodes were able to cause mortality on the insect. High mortality rates were accomplished by the two Steinernema species. The most efficient entomopathogenic nematode against small larvae was S. feltiae which attained 98.9% mortality followed by S. carpocapsae which caused 91.1% mortality after 8 days of exposure. Similarly, S. feltiae and S. carpocapsae killed 87.8 and 63.3% of the exposed large larvae on wheat treated with 50000 IJs/ml after 8 days of exposure. In contrast, at the highest dose, H. bacteriophora was less effective than S. carpocapsae and S. feltiae since it caused 76.7 and 60.0% mortalities to exposed small and large larvae after 8 days of exposure. The effectiveness of all three entomopathogenic nematodes was increased at higher doses and longer exposures. The findings of the current study indicate that entomopathogenic nematodes are efficient biological control organisms of T. granarium larvae infesting stored-wheat.