Most research on plant-pollinator communication has focused on sensory and behavioral responses to relatively static cues. Floral rewards such as nectar, however, are dynamic, and foraging animals will increase their energetic profit if they can make use of floral cues that more accurately indicate nectar availability. Here we document such a cue-transient humidity gradients-using the night blooming flowers of Oenothera cespitosa (Onagraceae). The headspace of newly opened flowers reaches levels of about 4% above ambient relative humidity due to additive evapotranspirational water loss through petals and water-saturated air from the nectar tube. Floral humidity plumes differ from ambient levels only during the first 30 min after anthesis (before nectar is depleted in wild populations), whereas other floral traits (scent, shape, and color) persist for 12-24 h. Manipulative experiments indicated that floral humidity gradients are mechanistically linked to nectar volume and therefore contain information about energy rewards to floral visitors. Behavioral assays with Hyles lineata (Sphingidae) and artificial flowers with appropriate humidity gradients suggest that these hawkmoth pollinators distinguish between subtle differences in relative humidity when other floral cues are held constant. Moths consistently approached and probed flowers with elevated humidity over those with ambient humidity levels. Because floral humidity gradients are largely produced by the evaporation of nectar itself, they represent condition-informative cues that facilitate remote sensing of floral profitability by discriminating foragers. In a xeric environment, this level of honest communication should be adaptive when plant reproductive success is pollinator limited, due to intense competition for the attention of a specialized pollinator.pollination biology | honest signaling | floral display P lant-pollinator relationships-like all mutualisms-strike a tenuous balance between the conflicting interests of foraging animals and flowering plants (1, 2). For flowering plants, pollinator attraction through floral density, form, color, pattern, and odor is necessary but insufficient to ensure effective pollination. Ideally, pollinators should transfer pollen between conspecific plants in ways that result in favorable levels of outcrossing (3) and reduced pollen loss (4). Flowers commonly manipulate pollinator movement by varying quality or quantity of floral nectar. The offer of variable amounts of nectar (5, 6), toxic nectar (7, 8), or an empty promise of nectar elicit similar results: pollinators leave plants sooner, reducing for example geitonogamous inbreeding (if selfcompatible) or pollen discounting (if self-incompatible).The availability of floral rewards often coincides with floral display and pollinator activity on a gross temporal scale (i.e., hours) (9, 10). Nevertheless, most pollinators encounter rewardless ("empty") flowers on a finer temporal scale (i.e., minutes), often due to recent visitation by another animal. From the pollin...

The European grape berry moth is an important pest in vineyards. Males respond to the female-produced sex pheromone released from a piezo nebulizer in a dosedependent manner in a wind tunnel: <50% arrive at the source at 5-50 pg/min (underdosed), 80% arrive at 100 pg/ min to 10 ng/min (optimal) and <20% arrive at 100 ng/min (overdosed). Males responding to overdosed pheromone show in Xight arrestment at 80 cm from the source. Host plant chemostimuli for Eupoecilia ambiguella increase the responses of males to underdosed and overdosed pheromone. (Z)-3-hexen-1-ol, (+)-terpinen-4-ol, (E)--caryophyllene and methyl salicylate released with the underdosed pheromone cause a signiWcant increase in male E. ambiguella Xying to the source. Time-event analysis indicates a positive correlation between faster activation and probability of source contact by the responding males. The four host plant compounds added to the overdosed pheromone permitted males to take oV faster and with a higher probability of Xying to the source. This suggests that perception of host plant products with the sex pheromone facilitates male E. ambiguella to locate females on host plants, lending credence to the hypothesis that plant products can signal rendezvous sites suitable for mating. Keywords

The foraging decisions of flower-visiting animals are contingent upon the need of an individual to meet both energetic and osmotic demands. Insects can alter their food preferences to prioritize one need over the other, depending on environmental conditions. In this study, preferences in nectar sugar concentrations (0, 12, 24 %) were tested in the hawkmoth Manduca sexta, in response to different levels of ambient humidity (20, 40, 60, and 80 % RH). Moths altered their foraging behavior when placed in low humidity environments by increasing the volume of nectar imbibed and by consuming more dilute nectar. When placed in high humidity environments the total volume imbibed decreased, because moths consumed less from dilute nectars (water and 12 % sucrose). Survivorship was higher with higher humidity. Daily foraging patterns changed with relative humidity (RH): moths maximized their nectar consumption earlier, at lower humidities. Although ambient humidity had an impact on foraging activity, activity levels and nectar preferences, total energy intake was not affected. These results show that foraging decisions made by M. sexta kept under different ambient RH levels allow individuals to meet their osmotic demands while maintaining a constant energy input.

Plant volatiles play an important role in the lives of phytophagous insects, by guiding them to oviposition, feeding and mating sites. We tested the effects of different host-plant volatiles on attraction of Lobesia botrana males to the female-produced sex pheromone, in a wind tunnel. Addition of volatile emissions from grapevines or individual plant volatiles to pheromone increased the behavioral responses of L. botrana males over those to pheromone alone. At a low release rate (under-dosed) of pheromone, addition of (E)-β-caryophyllene, (Z)-3-hexenyl acetate, 1-hexanol, or 1-octen-3-ol increased all behavioral responses, from activation to pheromone source contact, while addition of (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-β-farnesene, (Z)-3-hexenol, or methyl salicylate affected only the initial behavioral responses. Dose-response experiments suggested an optimal release ratio of 1:1000 (sex pheromone: host plant volatile). Our results highlight the role of plant volatiles in the sensory ecology of L. botrana.