Biology of Calliopsis pugionis (Hymenoptera: Andrenidae): Nesting, Foraging, and Investment Sex Ratio

Author： VISSCHER P. KIRK DANFORTH BRYAN N.

Publisher： Entomological Society of America

ISSN： 1938-2901

Source： Annals of the Entomological Society of America, Vol.86, Iss.6, 1993-11, pp. : 822-832

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Abstract

Calliopsis pugionis Cockerell usually nests in dense aggregations, with up to 1,650 nests per m², in areas of bare soil. A female provisions one cell each day with pollen from composites, here Encelia and Hemizonia, usually in three or four pollen foraging trips, followed by a trip in which she collects nectar and pollen for her own consumption. Matings take place both on flowers and at nest sites. Males compose 70.8% of the larvae provisioned. Investment sex ratio (M/F) ranges from 1.07 to 2.43 when estimated from several measures of cost, including adult dry weight, prepupal wet weight, meconia weight, pollen trip foraging time, total foraging time, and number of days. The best estimate of investment sex ratio is probably about 2. Quantitative predictions of effect on sex ratio of differential parasitism of males and females by a cleptoparasitic bee, Holcopasites ruthae Cooper, are derived. These account for only some of the male bias in investment sex ratio; other factors could include local resource competition.