Moths sense but do not learn flower odors with their proboscis during flower investigation

Insect pollinators, such as the tobacco hawkmoth Manduca sexta, are known for locating flowers and learning floral odors by using their antennae. A recent study revealed, however, that the tobacco hawkmoth additionally possesses olfactory sensilla at the tip of its proboscis. Here, we asked whether this second ‘nose’ of the hawkmoth is involved in odor learning, similar to the antennae. We first show that M. sexta foraging efficiency at Nicotiana attenuata flowers increases with experience. This raises the question whether olfactory learning with the proboscis plays a role during flower handling. By rewarding the moths at an artificial flower, we show that, although moths learn an odor easily when they perceive it with their antennae, experiencing the odor just with the proboscis is not sufficient for odor learning. Furthermore, experiencing the odor with the antennae during training does not affect the behavior of the moths when they later detect the learned odor with the proboscis only. Therefore, there seems to be no cross-talk between the antennae and proboscis, and information learnt by the antennae cannot be retrieved by the proboscis

Acetoin is a key odor for resource location in the giant robber crab Birgus latro

The terrestrial and omnivorous robber crab Birgus latro inhabits islands of the Indian Ocean and the Pacific Ocean. The animals live solitarily but occasionally gather at freshly opened coconuts or fructiferous arenga palms. By analyzing volatiles of coconuts and arenga fruit we identified five compounds, including Acetoin, which are present in both food sources. In a behavioral screen performed in the crabs’ habitat, a beach on Christmas Island, we found that of 15 tested fruit compounds Acetoin was the only volatile eliciting significant attraction. Hence, Acetoin might play a key role in governing the crabs’ aggregation behavior at both food sources

Transition from sea to land: olfactory function and constraints in the terrestrial hermit crab Coenobita clypeatus

The ability to identify chemical cues in the environment is essential to most animals. Apart from marine larval stages, anomuran land hermit crabs (Coenobita) have evolved different degrees of terrestriality, and thus represent an excellent opportunity to investigate adaptations of the olfactory system needed for a successful transition from aquatic to terrestrial life. Although superb processing capacities of the central olfactory system have been indicated in Coenobita and their olfactory system evidently is functional on land, virtually nothing was known about what type of odourants are detected. Here, we used electroantennogram (EAG) recordings in Coenobita clypeatus and established the olfactory response spectrum. Interestingly, different chemical groups elicited EAG responses of opposite polarity, which also appeared for Coenobita compressus and the closely related marine hermit crab Pagurus bernhardus. Furthermore, in a two-choice bioassay with C. clypeatus, we found that water vapour was critical for natural and synthetic odourants to induce attraction or repulsion. Strikingly, also the physiological response was found much greater at higher humidity in C. clypeatus, whereas no such effect appeared in the terrestrial vinegar fly Drosophila melanogaster. In conclusion, our results reveal that the Coenobita olfactory system is restricted to a limited number of water-soluble odourants, and that high humidity is most critical for its function

The olfactory coreceptor IR8a governs larval feces-mediated competition avoidance in a hawkmoth

Finding a suitable oviposition site is a challenging task for a gravid female moth. At the same time, it is of paramount importance considering the limited capability of most caterpillars to relocate to alternative host plants. The hawkmoth, Manduca sexta, oviposits on solanaceous plants. Larvae hatching on a plant that is already attacked by conspecific caterpillars face food competition. Here, we show that feces from conspecific caterpillars are sufficient to deter a female M. sexta from ovipositing on a plant. Furthermore, we not only identify the responsible compound in the feces but also localize the population of sensory neurons that governs the female’s avoidance. Hence, our work increases the understanding of how animals cope with a competitive environment

Host plant constancy in ovipositing Manduca sexta

Many pollinating insects exhibit flower constancy, i.e. they target flower species they have already experienced and fed from. While the insects might profit from reduced handling costs when revisiting similar flowers, flower constancy, in addition, is of benefit for the plants as it guarantees pollen transfer to conspecifics. Here we investigate whether the previous experience of an insect can also result in oviposition constancy, i.e. whether ovipositing on a given plant species will drive future oviposition preference in a female insect. We show that female hawkmoths (Manduca sexta), after having oviposited on a given plant species only once, indeed will prefer this plant in future oviposition choices. As oviposition preference is even affected 24 h after the moth has oviposited on a given plant, long term memory seems to be involved in this oviposition constancy. Our data furthermore suggest that, as shown for flower constancy, ovipositing moths increase their handling efficiency by targeting those host plants they have already experienced