Animals exploiting their familiar food items often avoid spatio-temporal aggregation with others by avoiding scents, less rewarding areas or visual contacts, thereby minimizing competition or interference when resources are replenished slowly in patches. When animals are searching or assessing available food sources, however, they may benefit from reducing sampling costs by following others at food sites. Therefore, animals may adjust their responses to others depending on their familiarity with foraging situations. Here, we conducted field experiments to test whether nectar-collecting bumble bees make this adjustment. We allowed free-foraging bees to choose between two inflorescences, one occupied by a conspecific bee and another unoccupied. When bees were presented with flowers of a familiar type, they avoided occupied inflorescences. In contrast, bees visited an occupied inflorescence when the flower type was unfamiliar. To our knowledge, this is the first report suggesting that animals adjust their responses to feeding conspecifics depending on their familiarity with food sources. Such behavioural flexibilities should allow foragers to both explore and exploit their environments efficiently.

Genetic differentiation can be promoted allopatrically by geographic isolation of populations due to limited dispersal ability and diversification over time or sympatrically through, for example, host-race formation. In crop pests, the trading of crops across the world can lead to intermixing of genetically distinct pest populations. However, our understanding of the importance of allopatric and sympatric genetic differentiation in the face of anthropogenic genetic intermixing is limited. Here, we examined global sequence variation in two mitochondrial and one nuclear genes in the seed beetle Callosobruchus maculatus that uses different legumes as hosts. We analyzed 180 samples from 42 populations of this stored bean pest from tropical and subtropical continents and archipelagos: Africa, the Middle East, South and Southeast Asia, Oceania and South America. For the mitochondrial genes, there was weak but significant genetic differentiation across continents/archipelagos. Further, we found pronounced differentiation among subregions within continents/archipelagos both globally and within Africa but not within Asia. We suggest that multiple introductions into Asia and subsequent intermixing within Asia have generated this pattern. The isolation by distance hypothesis was supported globally (with or without continents controlled) but not when host species was restricted to cowpeas Vigna unguiculata, the ancestral host of C. maculatus. We also document significant among-host differentiation both globally and within Asia, but not within Africa. We failed to reject a scenario of a constant population size in the recent past combined with selective neutrality for the mitochondrial genes. We conclude that mitochondrial DNA differentiation is primarily due to geographic isolation within Africa and to multiple invasions by different alleles, followed by host shifts, within Asia. The weak inter-continental differentiation is most likely due to frequent inter-continental gene flow mediated by human crop trade.

Summary1. Spatio-temporal variation in resource availability is often large and unpredictable. When animals need to find and sample novel foods, therefore they may prefer to choose food sources with feeding conspecifics or odour left by the conspecifics. This behaviour (local enhancement) would be favoured, especially if it decreases the time spent on food-finding and subsequent decision-making. In laboratory experiments we tested if naive bumble bees use local enhancement, and to what degree it could reduce the time spent on finding and sampling novel flowers. 2. When naive bees were presented with a pair of equally rewarded artificial or real flowers in a flight cage, they preferred to land and feed on the flower where a dead conspecific was attached. The presence of conspecifics reduced the time spent on detecting floral reward, which was significant only when bees chose between real flowers. In a similar pairwise choice, bees landed on artificial flowers with a dead conspecific wrapped in plastic more frequently than on flowers with the same-sized plastic wrap including no bees, which suggests that visual cues have important influences on the bees' flower choice. 3. Effects of conspecifics on flower choice and food detection time were most evident when they were attached to real flowers, and least evident when they were wrapped in plastic. These results suggest that the presence of conspecifics on flowers has stronger effects on bees' decision-making as the attractiveness of flowers increases, and that bees use both visual and non-visual cues to recognize conspecifics on flowers. 4. If the benefit of saving time were universal, the use of local enhancement would also be advantageous when bees switch between focal flower species or sites in response to temporal changes in resource availability.

Larval competition curves and resource sharing patterns of 5 strains of CaUosobruchus maculatus (iO~ yQ, aaQ, wO~ and tQ.) were examined. Offspring emergences as a function of the initial larval density were recorded to construct competition curves. Elytron length of emerged adults was used as the indicator of resource sharing patterns among competing larvae inside a bean.In the large beans, strain iQ showed a saturated competition curve and tQ strain showed a humped curve. Competition curves of the other 3 strains (yQ, aaO~ and wQ.) were between those two extremes. In the small beans, strains iQ and tQ. also showed a saturated and a humped competition curves, respectively, whereas the competition curves of the 3 intermediate scramble strains could not be distinguished from that of the iQ strain. Thus, the classification based on competition curves was sensitive to the resource condition (bean size). In both the large and the small beans, the elytron lengths of iQ strain remained constant irrespective of initial larval density.On the contrary, the elytron lengths of the 4 other strains decreased monotonically with higher initial larval density. Thus, the judgment based on the resource sharing pattern was shown to be robust. Only iQ strain should be designated as a contest type, and the remaining strains as scramble types. Contest and scramble types in C.maculatus were also compared with those observed in C. analis and C. phaseoli using competition curves, resource sharing patterns, and other physiological characters.

Callosobruchus maculatus has both contest and scramble competition strategies. The currently existing theoretical models using game theory suggest that the contest strategy should be selected for. However, most geographic strains of C. maculatus show scramble competition. We experimentally crossed the representative strains of contest and scramble. We expressed the degree of contest competition by a continuous value named the C‐value, which ranges from zero (pure scramble) to unity (pure contest). The competition types expressed in the C‐value were genetically additive. Their larval developmental rates were negatively correlated with C‐values. Multiple‐generation experiments of the mixed strains confirmed that there were no overwhelming advantages of contest over scramble type. Most of the mixed strains remained in the intermediate states. We discuss the results in terms of the resource size necessary for developmental success and developmental speed.