Life history comparison between two competitive Aleochara species in the cabbage root fly, Delia radicum: implications for their use in biological control

This study evaluates the efficacy of Aleochara bilineata Gyll and Aleochara bipustulata L. (Coleoptera: Staphylinidae) as biological control agents ag ainst the cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae). Biolo gical and demographic characters are documented and comparisons made betwee n the two species. The following results were obtained: (1) The reproductive potential and longevity of A. bipustulata females are significantly higher than those of A. bilineata. These differences are corr elated with the biology and ecology of the hosts of both species. (2) Under laboratory conditions the rate of increase (r(m)) of both staphyl inids species is significantly higher than that of the pest and their major competitor Trybliographa rapae West. (Hymenoptera:Figitidae). This may ind icate that A. bilineata and A. bipustulata can be effective biological cont rol agents. (3) Aleochara bilineata appears to be the most interesting biological contr ol agent against D. radicum, because of its higher rate of increase, higher host specificity and host acceptance, and a development time which is well synchronised with that of its host. With its higher competitive ability, a population of A. bilineata may increase even if competition occurs. Howeve r, A. bipustulata presents interesting biocontrol characteristics, but the best strategy may be only to use the potential of its natural populations.