INSECT INVOL VEMENT IN BACTERIAL DISEASES AND OTHER DISEASES AND DISORDERS OF CUCURBITS

摘要

The striped cucumber beetle (Acalymma vittatum) is by far the most important insect pest of cucurbits, particularly in New York, the northeastern states, and reaching into eastern Canada. In addition to cause direct crop injury to cucurbits by adult feeding, and occasional damage to roots by larval feeding, the striped cucumber beetle is most important as a vector of plant diseases, and in particular bacterial wilt that affects most cucurbits (Erwinia tracheiphfla). Cucumber beetles, and the closelyrelated Diabrotica species (Diabrotica undecimpunctata or the spotted cucumber beetle), are attracted to cucurbits by naturally occurring bitter cucurbitacins (oxygenated tetracyclic terpenes), which, as an aside, has also be used to enhance insecticidalcontrol. Cucumber cultivars with the non-bitter allele (bi) such as found in 'Country Fair' and 'Marketmore 80', are less preferred by cucumber beetles. Spotted beetles are also attracted to cucurbit flowers by blossom volatiles (indoles). Beetles causedirect damage to cotyledons, developing young leaves, blossoms, pumpkin fruit and handles (peduncles), which can make the fruit unmarketable. Bacterial transmission from overwintered beetles in the spring to young cucurbits occurs when contaminated fecal material comes in contact with wounds caused by beetle feeding. E. tracheiphila only multiplies in the xylem of susceptible cucurbits (pumpkins, summer squash, winter squash, muskmelons, cucumbers, but not watermelon) so the massing of beetles during the feeding process near veins will enhance transmission of bacteria from fecal matter. Besides vectoring bacterial wilt, striped cucumber beetle larvae have been shown to transmit Fusarium wilt of muskmelon, and adults (western striped cucumber beetle and spotted cucumber beetle) also transmit squash mosaic virus, which is primarily a concern for muskmelons and cantaloupes. A single dominant allele in cucumber is known to confer resistance, but in a homozygous state, undesirable associated problems occur. Growers generally rely on insecticides for control (imidacloprid, carbaryl, etc.) when the crop is threatened, especially if bacterial wilt is known to be a problem in the growing area.