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Japanese Beetle News

Current information for homeowners and agricultural producers

A Whole Lot of Info About....Grubs


Any discussion of Japanese Beetles would not be complete without a good discussion of this insect's larval stage, termed the white grub. Area producers can testify to quite an increase in grub observations over the last decade, but several beetle larvae can actually be classified as white grubs. So which grub is which? How does one tell the difference?

Four "grub groupings" are commonly recognized as possible corn pests. They include the "True" White Grubs, the Annual White Grubs, the Green June Beetle Grubs, and the Japanese Beetle Grubs. Identification can often be made via a hand lens and examination of hair arrangements on the tail end.

True White Grubs, the historically recognized corn pests, are commonly known as May/June beetles. Grubs belonging to this group have two rows of hairs located on the underside of the tail end, which can be observed with a hand lens. The grubs spend a few winters as larvae and pupate about mid-summer following their last overwintering period.

The larvae of the southern masked chafer are commonly termed "annual white grubs." These grubs pass through their grub-like stage in one year. The underside of their tail end has hairs arranged in a more random fashion.

Another possible, all be it rare grub pest of corn, is termed the Green June Beetle Grub. Also an annual grub, this native insect tends to be more of a pasture and lawn problem than a problem in field crops. The tail end of this grub also is marked by two rows of hairs, somewhat like the True Grub, but there is one key difference. The Green June Beetle's legs are inefficient so these grubs actually roll over and crawl on their backs. If in doubt as to whether a grub find is a true white grub or a Green June Beetle grub, the crop scout can simply lay the grub down and watch how it moves. The adult stage of this insect is a metallic green beetle which often flits madly about lawns during the mid summer.

As noted in previous sessions, Japanese Beetles have gained a lot of attention over the last several growing seasons as adult beetles have clipped corn silks and defoliated some ornamentals in  east-central and central Illinois. Many producers may not realize that the larva of this beetle is also a grub. An annual grub, native to Japan, which first made an appearance in the U.S. during the early 1900's, Japanese Beetle grubs can be identified by a "V-shaped" arrangement on hairs on the tail.


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