EFFECTS OF INSECTICIDES ON MOVEMENT, NICTATION, AND INFECTIVITY OF STEINERNEMA-CARPOCAPSAE

Movement, nictation, and infectivity of Steinernema carpocapsae strain All were compared for ensheathed (EnJ) and desheathed (DeJ) infective juveniles exposed to the insecticides acephate, dichlorvos, methomyl, oxamyl, or permethrin. Nematode response to various solutions include d normal sinusoidal movement, uncoordinated motion, twitching, convuls ion or formation of a pretzel shape, an inactive ''S'' posture with fi ne twitching, or a quiescent straight posture. The Dej displayed these movements at lower concentrations of each insecticide than did Enj. I n petri dish bioassays, insecticide-treated EnJ caused generally lower mortality in the common cutworm, Spodoptera litura, than did Enj alon e but caused greater insect mortality than did insecticides alone. Nem atode response to chemicals was more clearly demonstrated by nictating behavior than by the movement bioassay. Nictation of Dej was suppress ed by the test chemicals at low concentrations, except for acephate an d permethrin. Nictating EnJ or Dej, regardless of chemical treatment, killed host insects faster than did non-nictating juveniles. Insectici des that enhance nictating behavior at certain concentrations ma be us ed for mixed applications with nematodes.