Behavior and Phenology of a Specialist Bee (Dieunomia) and Sunflower (Helianthus) Pollen Availability

Abstract

The phenological relationships between nesting behavior of a specialist, solitary bee, Dieunomia triangulifera, and the flowering of its primary pollen source, Helianthus annuus, were studied for 3 yr at a site in northeastern Kansas, which contained between 50 000 and >150 000 nests. Activity patterns of D. triangulifera are closely synchronized with pollen availability on nearby sunflower plants in three ways: (1) each year, D. triangulifera became active within days of the beginning of the local sunflower bloom, and the emergence schedule of the entire population at the nest site was timed such that all females had constructed nests and were collecting pollen at peak bloom; (2) over a season the greatest numbers of provisioning females were active at peak bloom, when pollen was most abundant; and (3) over the day, females made more trips, each of which took less time when pollen was most abundant on nearby flowers than when it was scarce. Between seasons, female reproductive success varied positively with the availability of H. annuus pollen. When pollen was abundant, and the population at the nest site was low, °3 times more cells were provisioned than the following year when the bee population was high and pollen abundance declined. Furthermore, 20 pollen—collecting bee species (10 specialists and 10 generalists), besides D. triangulifera, used an estimated 68% of the available sunflower pollen at this site. These data suggest that resource limitation is important in shaping patterns of provisioning behavior in D. triangulifera. Other behaviors presumably related to reproductive success were variable and suggest resources were not limiting: (1) all females did not forage on each day, even at peak bloom; (2) variance in both trip durations and the numbers of trips made per day was large; and (3) females produced far fewer eggs in their lifetime than apparently possible. We suggest that the apparently conflicting evidence for resource limitation may be explained by a physiological limit on the rate of egg production; in such a case, the effects of resource limitation, while clearly important, might not be the primary factor limiting reproductive output. Female D. triangulifera benefit by being synchronized with their resource. Daily and seasonal synchrony enable females to collect a greater amount of pollen during shorter foraging trips. The translates into higher mean reproductive success and, at the population level, allows more females to be supported by the pollen produced from nearby plants. In short, those females that are synchronized with the sunflower bloom effectively increase their own resource availability. This phenomenon may be general, especially in short—lived organisms, i.e ., the evolution of specialization may be associated with fitness benefits based on synchrony with a preferred food source.

Wild bees enhance honey bees’ pollination of hybrid sunflower

“…If both foraging time and pollen were unlimited, then all florets would eventually be pollinated, even at low pollination efficiencies. In our system, however, pollen is limited (S.S.G., unpublished observation), as previously shown for sunflower (48). Thus, increased pollination efficiency by the principal pollinator, the honey bee, is likely to result in more total crop pollination and thus crop production.…”

“…We assumed that sufficient pollen and pollinators were available for florets to be pollinated within a 5-h window each day, based on daily bee activity patterns and observations of the eventual depletion of pollen from a field. A floret typically remained open for 1 day (unpublished data) (1,48).…”

Chemical composition of the ‘low quality’ pollen of sunflower (Helianthus annuus, Asteraceae)

“…Detailed studies on wild sunflower in its native range in Texas and Kansas have shown that many bee species take advantage of the open and accessible flowers with abundant pollen and nectar (Neff and Simpson, 1990;Minckley et al, 1994). However, the pollen protein content of Asteraceae is at the low end of the spectrum for beepollinated plants , and beekeepers consider these pollens to be a poor resource (Schmidt et al, 1987).…”

Nesting biology and phenology of a population of Halictus farinosus Smith (Hymenoptera, Halictidae) in northern Utah

“…The development of eusociality from solitary ancestors is considered one of the major transitions in evolution (Maynard Smith and Szathmary 1995). In order to understand how this transition took place, it is necessary to study organisms exhibiting primitive or weak eusociality, as is found in the subfamily Halictinae (Packer 1986;Packer 1992;Mueller 1996;Richards 2001;Soucy 2002;Richards et al 2010; and see Schwarz et al 2007).…”

“…In ground nesting bees the size of the food mass and the number that can be produced will depend on multiple environmental and biological factors including the size and activity levels of active foragers in the nest (Gathmann and Tscharntke 2002;Pereboom and Biesmeijer 2003) and the amount of available resources which, in turn, are highly dependent on weather and other environmental factors (Packer 1990;Minckley et al 1994;Richards and Packer 1996;Richards 2004). Repeat field studies of the same population can allow us to make comparisons between years to determine how weather patterns might affect phenology, productivity and sociobiology.…”