Bothynus gibbosus De Geer Coleoptera Scarabaeidae

Natural History

Distribution. Carrot beetle is found throughout the United States and southern Canada, and in north ern Mexico. This native insect is not usually considered to be a pest in northern states and in Canada, but can be injurious in the southern Great Plains.

Host Plants. This insect feeds on a fairly broad range of plants, and carrot is not one of the crops most frequently damaged. Chittenden (1902) argued that it was the most serious pests of carrot in the past century, and his opinion apparently prevailed. Carrot weevil, Listronotus oregonensis (LeConte), and carrot rust fly, Psila rosae (Fabricius), have since become much more serious pests of carrot, but the name of this beetle, though inappropriate, is unlikely to change. Hayes (1917) registered his dislike with the name "carrot beetle," but failed to suggest alternatives. The name "sunflower root beetle" might be a more accurate reflection of this insect's ecology.

Vegetable crops damaged by the carrot beetle include cantaloupe, carrot, celery, corn, parsnip, pepper, potato, sweet potato, tomato, and watermelon. Other crops injured are cotton, sugarbeet, sunflower, and perhaps oats and wheat. Weed hosts are quite numerous, and include prairie sunflower, Helianthus petiolaris; carelessweed, Amaranthus palmeri; horse-weed, Conyza canadensis; sawleaf daisy, Prionopsis ciliata; silverleaf nightshade, Solanum elaeagnifolium; and white rosinweed, Silphium albiforum. Most plant feeding is accomplished by adults. Larvae develop principally on decaying organic matter, and are often associated with animal manure. Occasionally, they feed on roots, however, and also are cannibalistic.

Natural Enemies. Several flesh flies (Diptera: Sarcophagidae) are parasitic on this beetle, including Gymnoprosopa argentifrons Townsend, Sarcophaga sar-racenioides Aldrich, S. cimbices Townsend, S. helicis Townsend, and S. rudis Aldrich (Hayes, 1917; Rogers, 1974). Additionally, undetermined fungi and bacteria are associated with eggs and larvae. A bulb mite, Rhi-zoglyphus echinopus (Fumouze and Robin) (Acari: Acar-idae) builds up to high densities on the overwintering adults. The importance of these natural enemies is unknown.

Life Cycle and Description. There is a single generation annually, with adults serving as the overwintering stage. Overwintering adults emerge in April-June, feed and oviposit. Larvae develop during the summer months, and produce a new brood of adults during July-October that overwinter and emerge the following spring.

  1. The eggs are deposited in the spring, often late May-July. The egg is slightly elliptical and white. It measures 1.5-2.5 mm long. Eggs are deposited in the soil, often at a depth of several centimeters. Their deposition may coincide with the presence of a suitable host plant, but this is not a prerequisite if organic matter is abundant. The duration of the egg stage is about 11 days (range of 7-22 days).
  2. The larvae are whitish with a brown head capsule. Larvae also acquire a bluish tint that is quite common among scarab grubs. They attain a length of about 3 cm. Larvae feed for about 52 days (range 40-70 days), passing through three instars. They then spend about seven days in a nonfeeding prepupal state while awaiting transformation to the pupal stage.
  3. Pupation occurs in the soil, usually during the period of August-September. Pupae measure about 15 mm long. Pupal color is whitish initially, but soon turns to brown. Duration of this stage averages 19 days (range 11-29 days).
  4. The adults are moderately large, and measure 11-16 mm long. They are reddish-brown to black. The elytra bear parallel impressions and coarse punctures. The ventral surface of the thorax and legs, but not the abdomen, are covered with a dense layer of hairs. Adults are active and feed during the autumn months, and then enter the soil to pass the winter. The adults are nocturnal, and highly attracted to lights. They are most active between dusk and 10:00 p.m. (Rogers et al., 1978). Because the beetles commonly damage other more fragile insects captured in light traps such as moths, the aforementioned authors suggested stratification of night-time sampling, with beetles being collected during early evening, but traps for moths being operated after 10:30 p.m. Overwintered adults are found abundantly on warm evenings as early as April, but return to the soil at daybreak. In South Carolina, King (1969) reported that adult emergence was greatly influenced by rainfall, but not temperature. He suggested that maximal emergence occurred following an accumulation of about 100 cm in the preceding 15 days. This apparently is not the case in Texas, however, where emergence occurs without such high levels of rainfall. Mating is reported to occur below-ground. The adults feed below-ground, and are the most damaging stage. (See color figure 123.)

The most complete biology of carrot beetle was given by Hayes (1917), but more recent studies by Bottrell et al. (1973) and Rogers (1974) are significant contributions.

Damage

Damage occurs on a wide variety of plants, but has been rigorously studied only on sunflower. In such a crop, where the seedlings do not emerge until mid-

Adoretus Sinicus Burmeister
Adult carrot beetle.

summer, it is the summer rather than the overwintering generation of beetles that causes injury. Damage to early season crops does occur, but it is caused by overwintering adults. Larval damage usually is insignificant. Adults feed at an average depth of 3.5 cm (range 0.6-12.9 cm), and a single adult can destroy virtually all the lateral roots of a small plant during the average feeding bout of 3.6 days duration. The primary, or tap root, is often only damaged at the surface. Sunflower varieties differ in susceptibility to injury, with perennial species less damaged (Rogers, 1980).

Management

Carrot beetles have proven to be difficult to control unless highly residual insecticides are applied to the soil. Granular and liquid formulations may be applied, but success is not always guaranteed (Bottrell et al., 1970; Rogers and Howell, 1973). Fortunately, they are usually associated with wild plants rather than crops. The principal exception is damage to sunflower, which can be a problem when this crop is grown in the southern Great Plains. Rogers et al. (1980) reported on evaluation of resistant sunflower varieties.

0 0

Post a comment