Beetle Resistance

Field studies were conducted in 1993 and 1994 to evaluate the effects of induced resistance in cucumber by plant growth-promoting rhizobacteria (PGPR) on numbers of the spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber, and the striped cucumber beetle, Acalymma vittatum (F.). Cucumber plant growth and yields were significantly (P<0.05) greater, and populations of cucumber beetles were significantly lower, on PGPR-treated cucumber than on nontreated cucumber. On dates when peak beetle populations were present, PGPR treatment resulted in significantly (P<0.05) greater cucumber beetle control than weekly applications of esfenvalerate insecticide. In no-choice greenhouse cage experiments with 3 cucumber cultivars, beetles infected with the cucurbit wilt pathogen, Erwinia tracheiphila, were released and allowed to feed on PGPR-treated or nontreated cucumber Plants. The incidence of cucurbit wilt disease was significantly (P<0.05) lower on PGPR-treated cucumber plants than on nontreated plants. These results indicate that PGPR-induced resistance may be more effective than insecticides for control of cucumber beetles and cucurbit wilt disease on cucumber. Possible mechanisms for PGPR-induced resistance against cucumber beetles are discussed.