University of California

Biology of Agathis unicolor (Schrottky) and Agathis gibbosa (Say) (Hymenoptera: Braconidae), primary parasites of the potato tuberworm


J. A. ?d?biyi
E. R. Oatman

Authors Affiliations

J. A. ?d?biyi was Assistant Professor of Entomology, Department of Agricultural Biology, University of Ibadan, Nigeria, formerly graduate student, Department of Entomology, University of California, Davis; Earl R. Oatman was Professor and Entomologist, Division of Biological Control, University of California, Riverside.

Publication Information

Hilgardia 45(5):123-151. DOI:10.3733/hilg.v45n05p123. August 1977.

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Studies were conducted on the biology, and on temperature and humidity responses, of Agathis unicolor (Schrottky), and exotic species. Results were compared with similar studies on the native species, A. glbbosa (Say), and their common host, the potato tuberworm, Phthorimaea operculella (Zeller). The two species of parasites were reared at several constant temperatures and humidities, and life-table data were obtained in each test environment. These data were used to calculate the intrinsic rate of natural increase, which was used as a bioclimatic index for each of the two species. The influence of several different constant temperatures and humidities on the parasites, and on host-parasite relationships, was evaluated on the basis of relative changes in the intrinsic rate of increase, developmental time, and the mean generation time.

The egg of A. unicolor is deposited in a ganglion of the ventral nerve cord of the host larva. Parasite larvae develop within the host body cavity and, after emergence, spin their silky-white cocoons inside the host cocoons. There are three larval ins tars, the first being both caudate and mandibulate, and the other two, hymenopteriform. The mean minimum developmental time from egg to adult emergence was 18 days at 26.7 C 50 ± 2 percent relative humidity (RH). Measurements and morphological descriptions of the immature stages are presented, and mating and ovipositional behavior of the adults are described. The optimum host density for maximum parasite progeny was 85 larvae per tuber. The biology of A. unicolor is similar to that of A. gibbosa.

Temperature and rate of development of both parasites were linearly related. However, at 35.0 C, A. unicolor could not develop beyond the prepupal stage. Longevity and reproductive periods were inversely related to temperature, and survivorship curves of both parasites conformed to the curves of physiological longevity.

On the basis of the intrinsic rate of natural increase, A. unicolor survived and reproduced from 21.1 to 32.2 C. Agathis gibbosa survived and reproduced from 21.1 to 35.5 C. Both parasites developed best at 50 percent relative humidity. Comparisons of the intrinsic rate of natural increase, developmental time, and mean generation time indicated that A. gibbosa would be better able to suppress populations of the host than A. unicolor.

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?d?biyi J, Oatman E. 1977. Biology of Agathis unicolor (Schrottky) and Agathis gibbosa (Say) (Hymenoptera: Braconidae), primary parasites of the potato tuberworm. Hilgardia 45(5):123-151. DOI:10.3733/hilg.v45n05p123
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