Summary1. Animal life span is constrained by ecology and physiology. The latter has been studied under controlled conditions, but little is known about determinants of life span under natural conditions. 2. We studied the relationships between length of adult life, magnitude of foraging activity, and environmental abiotic conditions in two bee species: a pollen specialist Andrena vaga (Andrenidae) and a pollen generalist Anthophora plumipes (Apidae). 3. Our research indicates that life span is driven both directly by climate and indirectly through climate-dependent activity patterns. We found a negative relationship between proportion of active days and length of life; in contrast, a high activity rate within the active days had no negative effect on longevity. 4. Individuals active during warm and/or wet days lived longer, with precipitation being a more important determinant of life span than temperature. 5. Timing of the first appearance at the site was also an important predictor of bee life span. Individuals that first appeared closer to the end of season (critical time horizon) lived a shorter time than individuals observed earlier. The first observed active day in the season was also correlated with seasonal temperature and precipitation. 6. We demonstrate that life span and activity patterns of wild populations of insects are regulated by a tractable interplay of ecological (mostly climatic) variables that were previously studied only in isolation or in vitro.
Intraspecific cleptoparasitism represents a facultative strategy advantageous for reducing time and energy costs. However, only a few studies about nesting dynamics have described intraspecific cleptoparasitic behaviour in obligate solitary bees. We focused on nesting dynamics with the characterisation of nest owner replacements and frequency of true usurpation in four aggregating species belonging to different phylogenetic lineages – Andrena vaga (Andrenidae), Anthophora plumipes (Apidae), Colletes cunicularius (Colletidae), and Osmia rufa (Megachilidae). Our study, based on the regular observation of individually marked females, shows that nest owner replacement affects 10–45% of nests across all of the studied species and years. However, 39–90% of these nests had been abandoned before owner change and thus true nest usurpations represent only a part of observed nest replacement cases. Females tend to abandon their nests regularly and found new ones when they live long enough, which is in accordance with risk-spreading strategy. We suggest that the original facultative strategy of observed solitary bees during nest founding is not cleptoparasitism per se but rather reuse of any pre-existing nest (similar to “entering” strategy in apoid wasps). This is supported by gradual increase of nests founded by “entering” during the season with an increase in the number of available nests. Although the frequent reuse of conspecific nests results in frequent contact between solitary females, and rarely, in the short-term coexistence of two females in one nest, we detected unexpectedly low level of conflict in these neighbourhood societies. We suggest that nesting dynamics with regular nest switching and reusing reduces long-term and costly intraspecific aggression, a key factor for the origin and evolution of sociality.
The consumption of sugar is an important part of the energy intake of social insect. Its monitoring provides information regarding the costs and efficiency of energy flow in a colony. This study aims at tracking the sugar flow from a sugar source to artificial bumblebee micro-colonies and at quantifying the amount of sugar consumed by the larvae. We developed a new method of sugar tracking that utilises an inert lanthanide complex (GdDOTA) dissolved in an aqueous sugar solution. The delayed defecation of bee larvae enabled the collection of all faeces from a cocoon. The amount of digested sugar corresponded to the amount of the lanthanide in the faeces, which was quantified using inductively coupled plasma spectrometric techniques. We highlight the possibility of the novel developed method to be extended for tracking the energy flow within a colony using up to 15 different metal markers without the necessity of killing individuals.
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