Bionomics of Aphidecta obliterata (L.) (Coleoptera: Coccinellidae), a predator introduced for control of the balsam wooly aphid on Mt. Mitchell, North Carolina

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Virginia Tech

A study of the bionomics of Aphidecta obliterata (L.), a predator introduced for control of the balsam woolly aphid, was conducted during 1965 and 1966, The study was undertaken to determine the life history and habits of A. obliterata in North Carolina and to determine its feeding habits.

In the laboratory, A. obliterata completed its life cycle in 53 days. The number of days in each stage was as follows: egg, 7.613 first instar, 6.17; second instar, 5.31; third instar, 6.83; fourth instar, 9.50; prepupa, 4.08; and pupa, 13.08.

Ninety~three per cent of the adults was identified correctly to sex by using head marking differences only. A distinct correlation was found between the length and the sex of the adult. One hundred per cent of the adults was identified correctly the sex by using both the head marking characteristics and the length of the adult.

An adult parasite, Medina luctuosa (Diptera: Tachinidae), was discovered in the 1966 shipment of A. obliterata adults from Austria. The use of X-ray to detect predators which were parasitized was found to te possible. All parasitized beetles were collected while holding the beetles in the laboratory at 68° F. and high humidity for 3 weeks.

A. obliterata eggs were observed in the field from June 2 to June 13 with an average of 8.0 eggs per cluster. The adults were observed feeding and resting mainly in the upper portions of the tree. Larvae were present from June 15 to late July. Adults were not seen after August 18.

Larvae of A. obliterata consumed the following average number of eggs per day: first instar, 20.8; second instar, 37.0; third instar, 56.2; and fourth instar, 115.3. A. obliterata adults consumed an average of 34.9 eggs and 11.8 adults daily. A straight line relationship with a correlation coefficient of 0.91 existed between larval length and the number of eggs consumed in 24 hours. The fourth instar larva consumed more eggs than the other 3 instars combined.

The 5 synthetic diets studied would not induce oviposition in A. obliterata females, and it is unlikely that they will lay eggs before feeding on their natural host in early spring.

The effects of predator end prey densities on interactions between A. obliterata larvae and Adelges piceae eggs were studied in the laboratory. Within the limits of the study, the per capita consumption of prey was reduced by increasing predator density. It was not due, however, to prey density but probably caused by crowding or interference which led to considerable cannibalism by the larvae.