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Natural enemies of agricultural pests, such as parasitoids and predators, often use chemical and visual cues in search of their hosts and prey, and they can learn the association between the cues and the host and prey presence. The braconid, egg-larval endoparasitoid wasp Ascogaster reticulata is a promising biological control agent for tortricid pests, such as Adoxophyes honmai, in tea plantations. Although previous studies revealed that A. reticulata uses contact chemicals released by tea plants in response to tortricid egg oviposition and that it can learn the associated cues, the diurnal wasp is also expected to use visual cues, especially color. Therefore, in this study, we investigated the innate color preference and associative color learning ability of A. reticulata. When a green paper and a paper of a different color (black, blue, red or yellow) was offered together to naive females of the wasp, the females spent less time on a black and blue papers. However, wasps trained to associate black or blue with the presence of a host egg-mass showed increased preference for these colors, whereas red- and yellow-trained wasps did not show changes in preference. Our findings indicate that A. reticulata uses colors, in addition to chemical cues, in host searching behavior and has the ability to learn colors associated with host presence.

1. Habitat loss and fragmentation potentially affect the performance of bees that forage nectar and pollen of plants in their habitats. In forest landscapes, silvicultural conifer plantations often have reduced and fragmented natural broadleaf forests, which seem to provide more floral resources for bees than do the plantations. 2. This study evaluated the effects of forest characteristics (i.e. elevation, area, edge length, and tree size of natural forests) on pollen diets (plant taxa assemblages of pollen grains in provisions) and total provision mass in oviposited chambers in nests made by a standardised number of Osmia cornifrons bees at 14 sites in a forestry area in central Japan. 3. From April to May, the numbers of nests and chambers per nest increased, and the provision mass per chamber decreased. Main pollen sources were Prunus at higher elevations in April and Wisteria at lower elevations in May, foraging on which increased the numbers of nests and chambers per nest. The provision mass per chamber was smaller at higher elevations in more fragmented natural forests. Decreases in the area of natural forests within the foraging range (400‐m radii) of O. cornifrons increased the utilisation of Rubus pollen and decreased the total provision mass. 4. These findings suggest that the loss and fragmentation of natural broadleaf forests change pollen diets and reduce the provision mass of mason bees, which may reduce the number and size of their offspring.

Some flowering plants signal the abundance of their rewards by changing their flower colour, scent or other floral traits as rewards are depleted. These floral trait changes can be regarded as honest signals of reward states for pollinators. Previous studies have hypothesized that these signals are used to maintain plant-level attractiveness to pollinators, but the evolutionary conditions leading to the development of honest signals have not been well investigated from a theoretical basis. We examined conditions leading to the evolution of honest reward signals in flowers by applying a theoretical model that included pollinator response and signal accuracy. We assumed that pollinators learn floral traits and plant locations in association with reward states and use this information to decide which flowers to visit. While manipulating the level of associative learning, we investigated optimal flower longevity, the proportion of reward and rewardless flowers, and honest- and dishonest-signalling strategies. We found that honest signals are evolutionarily stable only when flowers are visited by pollinators with both high and low learning abilities. These findings imply that behavioural variation in learning within a pollinator community can lead to the evolution of an honest signal even when there is no contribution of rewardless flowers to pollinator attractiveness.

Summary Plant species sometimes exhibit dynamic contrasting patterns in terms of reproductive traits. Floral colour change – the retention of old, non-productive, rewardless, but fully turgid flowers in an altered colour – has been considered as a plant strategy for enhancing pollinator attraction while minimizing visits to non-reproductive flowers. Considering the perceptive and cognitive abilities of animals, these advantages should apply in most systems. It seems paradoxical, and therefore, that floral colour change occurs in only a portion of angiosperms. This divergence may be explained if floral colour change adds as yet unknown costs or benefits under specific conditions. To explore such possibilities, we compared details of trait combinations and pollination consequences between a floral colour-changing (Weigela coraeensis) and a non-colour-changing (Weigela hortensis) species in a shared environment. Flowers of W. coraeensis secreted nectar for initial 2–3 days and remained white, after which they persisted for a few more days with discoloured, red purple petals and reduced nectar levels. Flowers of W. hortensis also secreted nectar for initial 2–3 days. They persisted for a few more days with the same colour and reduced amounts of nectar, but did so only when pollinators were scarce. Because only W. hortensis suffered from pollination difficulty at our site, both species retained their flowers for 4–5 days. Bees strongly preferred to visit W. coraeensis, leading to a greater proportion of seed set than in W. hortensis. In addition to their higher nectar productivity, only W. coraeensis plants offered bees colour difference as a visual cue to choose rewarding flowers and improve both long-term and short-term rates of nectar intake. By learning where to return, bees apparently responded to the difference in resource exploitability. Results indicate that floral colour change yields an additional benefit of attracting bee-like pollinators that return preferentially to more easily exploitable plants. Under conditions where benefits of enhancing both conspicuousness and exploitability cannot outweigh the costs of doing so, however, retention of rewardless flowers in the same colour and flexibility in floral longevity – as was adopted in W. hortensis – may become more advantageous in terms of saving metabolic and ecological costs.