Spectrophotometric Determination of Larval Ingestion Rates in the Spruce Budworm (Lepidoptera: Tortricidae)

The food intake of fourth, fifth, and sixth instar spruce budworm,Choristoneura fumiferanaClemens, was investigated by feeding larvae for 24 h artificial diet incorporating amaranth dye. Amaranth was selected because it followed Beer's law over a wide concentration range, mixed well with the meridic diet, could be extracted in ice-cold water, was not absorbed by larval tissue, had minimal feeding deterrence as well as marginal adverse chronic effects on the larvae, and finally had negligible effect on ingestion rate over a 24 h period. The results indicated that 6th instars consumed 20 times and 5th instars 3 times as much as 4th instars, but when compared on a body weight basis the ingestion rate was similar in all three instars. Temperature and photoperiod influenced the rate of food intake. The application of these findings in assessing defoliation to the forests as well as estimating dosage of pesticides for control of this species are discussed.