Spring Rose Beetle
Strigoderma arboricola Fabricius, Scarabaeidae, COLEOPTERA


DESCRIPTION

Adult - This slightly hairy beetle, sometimes referred to as the spring rose beetle, is basically greenish-black with a greenish-purple iridescence. The wing covers, however, are dull brownish-yellow in color. The beetle averages 10 to 12 mm long.

Egg - At first oval in shape, each white egg gradually enlarges, becoming more globose. From an initial size of 2 by 1.2 mm, the egg often increases in size to 2.5 by 2 mm.

Larva - The dirty white grub has a brown head and 3 pairs of forelegs. About 4 mm long when newly emerged, it reaches a maximum length of about 25 mm and resembles a common white grub in shape.

Pupa - The pupa is white when first formed but gradually darkens as it matures. It is approximately the same size and shape as the adult beetle.


BIOLOGY

Distribution - This beetle occurs from Canada southward through Kansas and North Carolina and is native to North America.

Host Plants - Adult beetles have been taken from many flowers, including those of clover, rose, blackberry, timothy, wild parsnip, dogfennel, and plantain. Larvae have been reported infesting roots of peanut, strawberry, sweet potato, and certain pasture grasses.

Damage - These grubs feed on most underground plant parts. In certain cases they have been known to strip the taproot bare. Sweet potatoes injured by these grubs have large but shallow feeding scars over their surface.

Life History - These insects overwinter as larvae in soil. In spring, grubs hollow out elongate, slightly curved earthen cells about 30 mm long. Within these cells, they spend approximately 6 days as inactive prepupae and 13 days as pupae. In Virginia, adult beetles usually emerge between May 15 and June 10. Further north, they often do not appear before the end of June. Several days after mating, females deposit eggs singly in soil (4 to 5 eggs/female based on lab studies). Eggs hatch an average of 17 days after deposition. By the time larvae begin feeding, at least one month has elapsed since adult emergence. Only one generation is completed each year.


CONTROL

White grub infestations are typically associated with fields formerly in sod or pasture. Such a relationship has not been documented for Strigoderma arboricola grubs, but it may exist nonetheless. Chemically, these grubs are controlled by granular insecticides incorporated into the soil before planting. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

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