Biological Responses of Rhynchophorus ferrugineus (Coleoptera: Curculionidae) to Steinernema carpocapsae (Nematoda: Steinernematidae)

Rhynchophorus ferrugineus (Coleoptera: Curculionidae) is becoming a serious problemin Mediterranean areas where it is well-adapted, and now is present even in the United States(California). The infestations are primarily in urban areas where chemical control is not advisable andmillion of Euros are spent to control it. The effects of the entomopathogenic nematode Steinernemacarpocapsae (Nematoda: Steinernematidae) on mortality, growth, as well as the immune activity ofR. ferrugineus larvae, were investigated. R. ferrugineus mortality exhibited a positive trend with thedosage and duration of exposure to S. carpocapsae. The median lethal dose and median lethal time,important to optimize the treatments, were calculated. S. carpocapsae also had a detrimental effect onR. ferrugineus weight. In vivo and in vitro effects of S. carpocapsae on the phagocytic responses of R.ferrugineus hemocytes also were recorded. S. carpocapsae was not encapsulated by R. ferrugineushemocytes. After 24 h, the number of hemocytes recorded in treated larvae was reduced. Toinvestigate the defensive abilities of R. ferrugineus humoral and cellular immune systems, speciÞcallyagainst the bacterium Xenorhabdus nematophila (Enterobacteraceae), the minimum inhibitory concentrationthat inhibits bacterial growth was measured. This is the Þrst time that this technique isapplied to entomopathogenic bacteria.