Alternation of Sex Ratio in a Partially Bivoltine Bee, Megachile rotundata (Hymenoptera: Megachilidae)

Tepedino, Vincent J.; Parker, Frank D.

doi:10.1093/aesa/81.3.467

Cited by 34 publications

(23 citation statements)

References 20 publications

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“…A reduction in M. rotundata offspring investment from 1 yr to the next is shown by the 2003 prepupae being heavier than the 2004 prepupae, possibly because of the fact that the Þeld in 2003 had about twice the number of ßowers as the Þeld in 2004. We also found in both years that prepupae destined to remain in diapause through the winter were signiÞcantly heavier than second-generation prepupae, as we may have predicted because M. rotundata adults that develop from diapausing prepupae are heavier than summer-emerging adults (Tepedino and Parker 1988). A positive relationship between body size and propensity to diapause has been reported in other insects (Nesin 1985, Danforth 1999, Menu andDesouhant In a 2-yr study with bees in enclosures on an alfalfa Þeld, according to density index, the total M. rotundata progeny (both sexes of second generation ϩ diapausing) produced that survived to adulthood and the sex ratios (M:F) of those progeny.…”

Section: Discussionsupporting

confidence: 74%

Nest Establishment, Pollination Efficiency, and Reproductive Success ofMegachile rotundata(Hymenoptera: Megachilidae) in Relation to Resource Availability in Field Enclosures

Pitts‐Singer¹,

Bosch

2010

Environ Entomol

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The alfalfa leafcutting bee, Megachile rotundata (Fabricius), is used to pollinate alfalfa, Medicago sativa L., for seed production in the United States and Canada. It is difficult to reliably sustain commercial M. rotundata populations in the United States because of problems with disease, parasites, predators, and unexplained mortality. One possible explanation for early immature mortality is that, relative to floral availability, superfluous numbers of bees are released in alfalfa fields where resources quickly become limited. Our objective was to determine how M. rotundata density affects bee nesting, pollination efficiency, and reproductive success. Various numbers of bees were released into enclosures on an alfalfa field, but only 10-90% of released female bees established nests. Therefore, a "bee density index" was derived for each enclosure from the number of established females and number of open flowers over time. As the density index increased, significant reductions occurred in the number of pollinated flowers, number of nests, and number of cells produced per bee, as well as the percentage of cells that produced viable prepupae by summer's end and the percentage that produced adult bees. The percentage of cells resulting in early brood mortality (i.e., pollen balls) significantly increased as the density index increased. We conclude that bee nest establishment, pollination efficiency, and reproductive success are compromised when bee densities are high relative to floral resource availability. Open field studies are needed to determine commercial bee densities that result in sustainable bee populations and adequate pollination for profitable alfalfa seed production.

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Section: Discussionsupporting

confidence: 74%

Nest Establishment, Pollination Efficiency, and Reproductive Success ofMegachile rotundata(Hymenoptera: Megachilidae) in Relation to Resource Availability in Field Enclosures

Pitts‐Singer¹,

Bosch

2010

Environ Entomol

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“…This was also suggested by Tepedino and Parker (1988) reporting on a study of Megachile rotundata, the semi-domesticated alfalfa leaf-cutting bee. They found strong, alternating sex ratio biases in the predicted directions, but virtually no overlap between generations.…”

Section: What Else Might Explain Male-biased Sex Ratios?mentioning

confidence: 58%

Sex ratios and life-history patterns of a solitary wasp, Trypoxylon (Trypargilum) politum (Hymenoptera : Sphecidae)

Brockmann

Grafen

1992

Behav Ecol Sociobiol

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Werren and Charnov (1978) and Seger (1983) proposed a model to explain a fairly common pattern of alternating sex ratio biases between generations in partially bivoltine insects. When first-generation males overlap and mate with females of the second generation, then females should bias sex ratios in favor of sons for the first generation and daughters for the second generation. In an intensive, 7-year study at four sites in northern Florida, pipe-organ mud-daubing wasps (Trypoxylon (Trypargilum) politum; Hymenoptera: Sphecidae) were found to have strongly male-biased sex ratios in the first or overwintering generation and 1:1 or female-biased sex ratios in the second or summer generation. These differences were not due to differences in mortality of the two sexes but rather resulted from changing female sex-allocation decisions. In some respects the mud dauber results fit Seger's model well: alternating sex ratios in partially bivoltine populations, first-generation males overlapping second-generation females and perhaps most convincingly, northern, univoltine populations do not have a male bias. Despite this qualitative fit, however, our data do not meet the quantitative predictions of the model. This could result from the fact that some assumptions of the model are not met by the life history of T. politum. Alternative explanations for alternating sex ratios include split sex ratios, seasonal differences in cost ratios, facultative maternal investment rules and facultative overwintering decisions by offspring. Despite the position that sex ratios have achieved in the modern study of evolution, it is clear that accurate, quantitative predictions on sex-allocation patterns demand the same detailed understanding of the biology of the organism that is required for the study of other adaptations.

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“…For example, Cowan (1981) found significantly female-biased investment ratios in two eumenid wasps but attributed these results to local mate competition and inbreeding (males establish territories at their natal nest entrance and mate with sisters). Furthermore, sex ratio is a highly plastic trait, varying within species of solitary bees within a season (Torchio and Tepedino 1980;Tepedino and Parker 1988;Frohlich and Tepedino 1986), between years (Tepedino and Torchio 1982) and as a function of nest substrate qualities (Tepedino and Torchio 1989). Therefore, any conclusions drawn from estimates of population sex ratio based on only one season should be made with caution.…”

Section: Estimating Parental Investment In Solitary Hymenopteramentioning

confidence: 99%

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

Danforth

1990

Behav Ecol Sociobiol

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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.

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Alternation of Sex Ratio in a Partially Bivoltine Bee, Megachile rotundata (Hymenoptera: Megachilidae)

Cited by 34 publications

References 20 publications

Nest Establishment, Pollination Efficiency, and Reproductive Success ofMegachile rotundata(Hymenoptera: Megachilidae) in Relation to Resource Availability in Field Enclosures

Nest Establishment, Pollination Efficiency, and Reproductive Success ofMegachile rotundata(Hymenoptera: Megachilidae) in Relation to Resource Availability in Field Enclosures

Sex ratios and life-history patterns of a solitary wasp, Trypoxylon (Trypargilum) politum (Hymenoptera : Sphecidae)

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

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