Beetles

Late Season Beetles in Pumpkins

There have been several reports from growers who have observed a number of striped beetles in their pumpkin or other cucurbit fields in the last month. Two different but similar-appearing beetles may be present in fields at this time of year - striped cucumber beetles (STCB, Acalymma vittatum (F)) and western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte). Both beetles have yellow wings with 3 black stripes and can be found in pumpkin and melon fields in late July through October. STCB have three straight-edged parallel longitudinal black stripes on their wings while WCR have three wavy stripes. STCB always have clearly defined stripes while the stripes on WCR are often wide and poorly defined. The easiest and most certain way to tell these beetles apart is to turn them over and look at their bellies. STCB have black abdomens while WCR have yellow abdomens.

STCB WCR-belly

Striped cucumber beetles mating with black belly

and western corn root worm beetle with extended

yellow belly

WCR adults concentrate their feeding on pollen and sometimes the developing fruit and are stimulated to feed on pumpkin plants and other cucurbits because of the presence of the plant-produced chemical cucurbitacin. WCR do not carry or transmit the bacterium that causes bacterial wilt of cucurbits. The larvae of WCR do not feed on pumpkin roots and will not reproduce in cucurbit fields. Adult WCR beetles emerge from corn fields in mid-late July. WCR overwinter as eggs, which were laid in corn fields in late summer.

Striped cucumber beetles overwinter as adults and become active early in the spring at which time they feed, mate and lay eggs in cucurbit fields. The adult beetle does carry the bacteria that cause bacterial wilt disease in cucurbits. However, in late summer it is doubtful that there will be any transmission of the bacteria to the extent it will cause any yield loss in the field. The problem in late summer and early fall with STCB, WCR and especially the spotted cucumber beetle, Diabrotica undecimpunctata howardi (Barber), is their feeding activity on the fruit. The beetles can build to large populations in the field and will feed on and scar developing pumpkin or melon fruit. Growers need to watch for their feeding activity both on the top side and soil-contact side of fruit. This feeding, even if just a small amount, can open the fruit to soil fungi and bacteria that will cause rots. One way to “divert” the attention of the beetles from the fruit is to maintain the foliage (and therefore flowers) for as long as possible. Once the foliage is lost, the beetles will begin to concentrate their feeding on the fruit. Pyrethroids should work well in controlling the beetles. Complete coverage of the fruit is necessary to prevent feeding damage.

beetle feeding

Severe Cucumber beetle feeding on pumpkin

For more information, contact Dr. Gerald Brust

Last updated: 11/2/2006