Effects of host plant and cucurbitacin on growth of larval Diabrotica undecimpunctata howardi

The effects of host plant and dietary cucurbitacin on the growth of larval southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber (Chrysomelidae: Luperini), were investigated. SCR were reared on four hosts: corn, Zea mays; peanuts, Arachis hypogaea; and two squash varieties, Cucurbita pepo cv. Ambassador (containing cucurbitacin D (0.08 mg g^-1 fr. wt.) = bitter), and C. pepo cv. Early Yellow Crookneck (lacking cucurbitacin = non-bitter). Larval growth was significantly greater on corn and peanuts than on either squash variety. After four weeks, adults had emerged from corn and peanut plants, while squash-reared larvae had not yet entered the pupal stage. There was no difference in larval growth on the two varieties of squash. Primary metabolite measurements showed no nutritional differences between the two squash varieties. Artificial diet experiments were used to test the effect of three concentrations of cucurbitacin D (0.0,0.1, and 0.6 mg g^-1 diet) on growth of larval SCR. Larvae reared on diet containing 0.6 mg g^-1 cucurbitacin weighed significantly less than larvae reared on diet containing 0.1 mg g^-1 or no cucurbitacin after 10 d. No significant difference in growth was measured between the 0.1 mg g^-1 diet and the 0.0 mg g^-1 diet. Results are discussed relative to theories about the relationship between diabroticites and cucurbitacins.