Adoretus sinicus Burmeister Coleoptera Scarabaeidae

Natural History

Distribution. This beetle is native to the Orient, where it is known from the Asian mainland, Formosa, Philippines, Indonesia, and several other islands. In the United States, Chinese rose beetle is known only from Hawaii, where it was first observed at Honolulu in 1891. By 1898 it had spread throughout the Hawaiian Islands and had become a serious pest. It is frequently intercepted on plant shipments sent from Hawaii to California, and has potential to establish in warm climates such as California and Florida.

Host Plants. This species has a very wide host range. Habeck (1964) noted that about 250 species in over 50 plant families had been documented as hosts, but that the actual range might include 600-700 species. Ornamentals, trees and fruits are damaged in addition to vegetables. It is reported to be the most important defoliator of beans in Hawaii, and also damages asparagus, Chinese cabbage, broccoli, corn, cucumber, eggplant, okra, and sweet potato. Among the most highly preferred plants are strawberry, Fragaria sp.; Rangoon creeper, Quisqualis indica; plumbago, Plumbago capensis; seagrape, Cocoloba uvifera; cacao, Theobroma cacao; macaranga, Macaranga grandiflora; castorbean, Ricinus communis; hibiscus, Hibiscus spp.; and heliconia, Heliconia spp.

Natural Enemies. Several parasitoids and predators were imported to Hawaii for biological suppression of Chinese rose beetle. None were successfully established, but two parasitoids that were imported and released in Hawaii for suppression of Oriental beetle, Anomala orientalis Waterhouse, also attack Chinese rose beetle. These parasitoids, Camposomeris mar-ginella modesta (Smith) (Hymenoptera: Scoliidae) and Tiphia segregata Crawford (Hymenoptera: Tiphiidae), were reported not to be very effective (Clausen, 1978). Nonetheless, C.m. modesta readily digs for, and parasitizes, grubs in open areas such as tilled fields, and Williams (1931) indicated that it was effective in agricultural fields. Unfortunately, this parasitoid is reluctant to forage in dense vegetation such as lawn grass, where Chinese rose beetle larvae also may develop. A wireworm, Conoderus exsul (Sharp) (Coleoptera: Elateridae), is reported to attack the larvae of Chinese rose beetle in preference to plant material. Larvae often are infected with the fungus, Metarhizium aniso-pliae, especially during the wet season.

Life Cycle and Description. This species completes a generation in 6-9 weeks during the summer, so several generations seem likely annually in Hawaii.

  1. The eggs are deposited in soil, usually within the upper 4 cm. The female burrows in the soil and creates a small chamber before oviposition, and leaves a single egg within. Females typically create 4-6 egg chambers in close proximity. The eggs are shining white initially, becoming dull creamy white before hatching. Eggs are oval, and measure about 1.4 mm long and 0.7 mm wide. Duration of the egg stage is about 12-14 days at 24°C and 8-12 days at 28°C.
  2. The larvae of Chinese rose beetle are not very destructive, feeding principally on decaying leaf material in the soil. In form, the larva is typical for a scarab beetle, with well-developed thoracic legs, a yellowish-brown head capsule, and a whitish body. The larva attains a length of about 35 mm prior to pupation. There are three instars. The head capsule widths of the instars measure about 1.2, 1.9, and 3.1 mm. Duration of the instars was reported to be 19.6, 16.8, and 34.3 days, respectively, during February-May. Development times were similarly reported to be 22.8, 14.5, and 44.4 days, respectively, during December-April. The final five days of the larval stage is a nonfeeding prepupal period.
  3. The pupa initially is yellowish white, gradually turning brownish before emergence of the adult. The pupa resembles the adult except that the elytra are reduced in size and twisted ventrally. The pupa measures about 13 mm long and 6-7 mm wide. Duration of the pupal stage is estimated at 11-17 days, averaging about 14 days.
  4. The newly emerged adult remains in the soil and does not feed for 3-5 days. The adult is reddish brown, but as it is clothed with a layer of fine scale-like white hairs, the brownish color tends toward gray. The beetle measures 7.0-10.0 mm and is relatively long and narrow in appearance. The adult is active at night, and during the day remains secluded under tree bark or organic debris, or buried in the soil at a shallow depth. Oviposition commences about seven days after mating. Fecundity under caged conditions averaged 54 (range 22-89) eggs, with maximum oviposition of 28 eggs per week.

The biology of this insect is incompletely described. Williams (1931) and Habeck (1964) provided some information on field biology. Habeck (1963) gave a complete description of the immature stages.

Damage

The adults are the destructive stage, and feed freely on the leaves, flowers, and buds of numerous plants. The interveinal feeding pattern in dicotyledonous

Adoretus Sinicus

plants results in a skeletonizing of foliage, and is fairly diagnostic. In monocotyledonous plants, however, veins as well as interveinal tissue are consumed. Photosynthetic rates of remaining plant tissue are more depressed following injury to monocot foliage, relative to dicot tissue (Furutani et al., 1990). Beetles preferentially feed upon tissues high in carbohydrates (Furutani and Arita, 1990). The larvae are commonly found in lawns, gardens, and flower beds, but do not attack living-plant tissue, so they are not destructive.

Management

The adults are attracted to light traps, but females are usually captured only after they have completed oviposition. They are also attracted to stressed or beetle-damaged plants, presumably because such plant produce ethylene in a gaseous form (Arita et al., 1988). Foliar insecticides are effective against adults.

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