DIFFERENT SENSITIVITIES OF THE SUGAR RECEPTOR OF THE LATERAL STYLOCONIC SENSILLUM IN 4TH-INSTAR AND 6TH-INSTAR LARVAE OF THE SPRUCE BUDWORMCHORISTONEURA-FUMIFERANA

Female fourth- and sixth-instar larvae, Choristoneura fumiferana, were tested individually for the response of the sugar cell on the lateral styloconic sensillum to 25 mM/l concentrations of 12 carbohydrates. T he spruce budworm showed an age-related change in responsiveness of th e sugar cell. The order of stimulating effectiveness for fourth-instar s was melibiose > sucrose > raffinose. These storage di- and trisaccha rides are present in the host plant at the beginning of budbreak. Sixt h-instars responded to sucrose > fructose > m-inositol. These findings are in accordance with those of a previous behavioural study on feedi ng preferences of sixth-instars. The response for both melibiose and r affinose does not change from fourth- to sixth-instars; however, it do es for sucrose, fructose and m- inositol.