Effect of a phloxine B-cucurbitacin bait on diabroticite beetles (Coleoptera: Chrysomelidae).

Cucurbitacin E glycoside, extracted from a bitter mutant of Hawkesbury watermelon [Citrulls lanatus (Thunb.) Matsum. & Nakai (Syn. Citrullus vulgaris Schrad)] is the active ingredient of a feeding stimulant for the corn rootworm complex. It is the primary component of a water-soluble bait that can be combined with toxins for adult diabroticite control. Studies were conducted using phloxine B (D&C Red 28), a xanthene dye, as the toxin. This dye was efficacious against Diabrotica undecimpunctata howardi Barber, spotted cucumber beetle, and Acalymma vittatum (F.), striped cucumber beetle, in cucumber plots and could be recovered from cucumber leaves for 8 d after treatment. The average amount of dye recovered per dead spotted cucumber beetle at 8 d after treatment was 0.173 microg. Concentrated and sugar-free fermented forms of the watermelon extract were developed and compared with the fresh juice in field applications on cucumber plants. There was no significant difference in mortality of beetles from phloxine B-bait prepared with fresh, fermented, or concentrated extract, although in laboratory studies, fermented juice had higher feeding stimulant activity.