THE ROLE OF CHEMOTACTIC STIMULI IN THE FEEDING BEHAVIOR OF SPRUCE BUDWORM LARVAE ON WHITE SPRUCE

Abstract

The effects of chemical stimuli on the feeding behavior of penultimate-instar larvae of the spruce budworm, Choristoneura fumiferana (Clem.), were investigated, especially in relation to the relative acceptability of staminate flowers, new vegetative shoots, and mature needles of white spruce, Picea glauca (Moench) Voss.Phagostimulants were extracted from the host plant tissues with 80% ethanol. Some substances known to be present in the extracts and some related compounds were investigated individually. The only substances that induced feeding responses in these tests were a number of sugars and the amino acid L-proline.In choice tests ethanol extracts of the staminate flowers were more acceptable than extracts of the shoots, and shoot extracts were more acceptable than extracts of the mature needles.The various host tissues differ quantitatively and qualitatively in the occurrence of some substances that significantly affect feeding behavior. The concentration of total sugars is greatest in the staminate flowers and least in the mature needles. Sugar concentration influenced feeding; the highest concentration encountered in the extracts evoked the greatest response. The difference in response to extracts of the various tissues was not attributable simply to differences in the sugar concentration.Staminate flowers contain much greater amounts of the amino acid L-proline than do the other tissues. Larvae offered a choice of sucrose plus L-proline or sucrose alone fed preferentially on the mixture. Similar but somewhat less pronounced responses were also noted with the related compounds, hydroxy-L-proline and L-glutamic acid.Pungenin occurs in appreciable amounts in mature spruce needles but is absent from, or present only in trace amounts, in new vegetative shoots. This glucoside deterred feeding but the difference in responses of larvae to extracts of the shoots and mature needles was not solely attributable to this effect. Shikimic acid and caffeic acid each stimulated feeding when present in mixture with sucrose. They may influence the differential feeding responses to the shoots and mature needles.