Factors Influencing Cucurbitacin-E-Glycoside Content in Bitter Hawkesbury Watermelon as Potential Synergist in Cucurbit Pest Management

Bitter Hawkesbury watermelon (BHW) Citrullus lanatus (Thunb.) Matsum. and Nakai (syn. Citrullus vulgaris Schad) contain high concentrations of cucurbitacin-E-glycoside (CEG), a compound that acts as an arrestant and feeding stimulant for diabroticine leaf beetles that are corn (maize) and cucurbit pests. Juice from BHW is used as feedstock to produce an insecticide synergist for improved chemical control of pests in cucurbit cropping systems. A positive linear relationship was observed between the CEG concentration of parent and offspring grown in open-pollinated field plots. However, subsequent experiments that explored the influence of parent and fruit maturity on CEG concentration did not confirm a relationship between accumulation patterns among offspring of half-sibling families. An effect of maturity was observed in that earlier harvested fruit had greater CEG concentrations than ripe or overripe fruit. In a field study, CIDETRAK L (active ingredient is BHW juice) was mixed with commonly used insecticides to enhance behavioral control of striped cucumber beetle Acalymma vittatum (F.) and squash vine borer Melittia cucurbitae (Harris). Equivalent control of A. vittatum and M. cucurbitae was observed on zucchini when treated with foliar applications of spinosad, acetamiprid, or lambda-cyhalothrin versus ground applications of the same products mixed with CIDETRAK L.