Provisioning behavior and the estimation of investment ratios in a solitary bee, Calliopsis (Hypomacrotera) persimilis (Cockerell) (Hymenoptera: Andrenidae)

Abstract

One aspect of behavioral ecology that has received considerable attention, especially by students of social insects, is the relative amount of energy invested by parents in the rearing of male versus female offspring. Sexual selection theory makes predictions about how individuals should allocate their total investment in the sexes. To test these predictions we must accurately quantify the relative "cost" incurred by a parent in the production of an average individual of either sex. Body weight ratios are the most common estimate of cost ratio, but the correspondence between offspring body weight and energetic investment on the part of the parent has rarely been determined. Calliopsis (Hypomaerotera) persimilis is a solitary, ground-nesting bee whose natural history makes it particularly convenient for studies of investment patterns and foraging behavior. Each day females construct and provision from 1 to 6 cells in linear, closely-spaced series. Each cell is provisioned with pollen from Physalis Wrightii flowers, which is collected on two or three foraging trips. However, the temporal sequence in which two-and three-trip foraging bouts occur is not random. Females invariably begin each day provisioning cells with three trips worth of pollen and usually switch to provisioning the latter cells of the day with just two trips worth of pollen. The sex of the offspring within the same co-linear series of cells also varies non-randomly -female offspring predominate in the first cells of each series and male offspring in the latter cells. The correspondence between the number of foraging trips to provision a cell, the total time spent foraging, and offspring sex was determined for 36 cells. The data indicate a close, though not absolute, relationship between the number of foraging trips and the sex of the offspring: males usually received two trips of pollen, though some received three, whereas female offspring invariably received three trips worth of pollen. A number of potential estimates of the relative cost of female and Present address: Department of Entomology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA male offspring production were calculated. Estimates of the cost ratio based on the amount of time spent foraging, adult dry body weight, and pollen ball dry weight all give similar values. Female offspring receive an energetic investment of from 1.3 to 1.5 times that of males. These results support the use of adult dry body weight ratios in the estimation of cost ratios.

Timing and size of daily pollen meals eaten by adult females of a solitary bee (Nomia melanderi) (Apiformes: Halictidae)

“…Pollen feeding was not restricted to day's end, as suggested for a few other ground-nesting solitary bees (Isenberg et al 1997;Danforth 1990Danforth , 1991. We found pollen masses in 36 % of the crops of nesting females caught after their first few foraging trips of the day and close to half of them by late morning (Figure 5a).…”

“…By evening, nearly all females had abundant pollen in both their crops and midguts, suggesting that they had eaten one recent pollen meal plus one (or more) meals earlier in the day. The few earlier studies, which only examined crop fill, reported just late-day Bfeeding tripsd uring nesting (Isenberg et al 1997;Danforth 1990Danforth , 1991. We found that female N. melanderi began gorging on pollen within hours of emergence and continued to eat daily pollen meals most, and possibly all, of their adult lives.…”

“…Based on similar premises, Michener (1974) incorporated pollen consumption at flowers in his diagram of material flow in solitary bees. Lind's concept of feeding trips has since been inferred from field observations of Perdita portalis (Andrenidae) (Danforth 1991) and Melissodes rustica (Apidae) (Cameron et al 1996) and confirmed for several species by dissections of females returning to the nest (Danforth 1989(Danforth , 1990Visscher and Danforth 1993). They bore no scopal pollen, but their crops contained nectar mixed with variable amounts of pollen.…”

The body size of the oil-collecting bee Tetrapedia diversipes (Apidae)

“…There are positive correlations of mother size and brood cell size (Tepedino and Torchio 1989), mother size and amount of food supplied (Boomsma and Eickwort 1993), brood cell size and amount of food supplied (Krombein 1967, Johnson 1990), amount of food supplied and size of emergent bees (Klostermeyer et al 1973, Danforth 1990, Johnson 1990, and brood cell size and size of emergent bees (Klostermeyer et al 1973, Kamm 1974, Alcock 1979, Tepedino and Torchio 1982. In Lasioglossum zephyrum bee size is correlated with brood cell size: the larger bees construct larger cells and larger bees emerge from larger cells (Kamm 1974).…”

“…In general, the nests have between 6 and 15 cells and construction time varies from 3 to 6 weeks (Alves dos Santos et al 2002). As obvious as it may seem few studies have analyzed the amount of food for the larvae and size of emerged bees (Klostermeyer et al 1973, Danforth 1990, Johnson 1990). However, in none of them was removed food from brood cells.…”