A larval aggregation pheromone as foraging cue for insectivorous birds

Gregariousness in lepidopteran larvae

The gregarious lifestyle of lepidopteran larvae is diverse and shaped by a complex interplay of ecological and evolutionary factors. Our review showed that the larval-aggregation behavior has been reported in 23 lepidopteran families, indicating multiple evolution of this behavior. Some larvae live in sibling groups throughout all larval instars and even pupation stages, which may result from the kin-selection. In contrast, group fusion may occur among different sibling or foraging groups of larvae and form larger aggregates, and the gregariousness of these species might be driven by the group-selection. While group size and foraging patterns vary greatly across species, it is generally associated with improved larval survivorship and accelerated development. However, the advantages of group living, such as facilitating feeding activities, adjusting the temperature, and defending natural enemies, may diminish along with development, with strong intraspecific competition occurring at later instars, even when food is abundant. Therefore, the group sizes and fission-fusion dynamics of certain gregarious lepidopteran larvae may be a consequence of their cost-benefit balance depending on various biotic and abiotic factors. Trail and aggregation pheromones, silk trails, or body contact contribute to collective movement and group cohesion of gregarious lepidopteran larvae. However, frequent contact among group members may cause the horizontal transmission of pathogens and pesticides, which may bring an integrated pest management strategy controlling gregarious lepidopteran pests.

Evidence of Cuticle Chemicals of Heortia vitessoides (Lepidoptera: Crambidae) Larvae Influencing the Aggregation Behavior of Conspecific Larvae

Heortia vitessoides (Lepidoptera: Crambidae) is a severe pest of Aquilaria plants, which produce high-priced agarwood. The larval stage of this pest is gregarious, usually forming large aggregates during young instars and becoming solitary during the fifth instar. We hypothesize that the cuticle chemicals of young-instar H. vitessoides larvae could promote larval aggregating, whereas the cuticle chemicals of late-instar larvae would no longer attract young-instar larvae. In this study, two-choice tests were conducted to evaluate the effect of cuticle extracts of second- and fifth-instar H. vitessoides larvae on the aggregation preference of second-instar larvae. Results show that significantly more larvae aggregated on the leaves treated with the hexane extract of second-instar H. vitessoides larvae than on untreated leaves. However, the hexane extract of fifth-instar larvae had no significant effect on the aggregation preference of the second-instar conspecific larvae. Interestingly, acetone extracts of both second- and fifth-instar H. vitessoides larvae repelled the second-instar conspecific larvae throughout the 8 h experiment. Our study shows that cuticle chemicals of H. vitessoides larvae may play a role in the group dynamics of this pest, which may contribute to screening novel attractants and repellents for H. vitessoides. Detailed chemical analyses of the extracts and identification of the compounds involved in larval attracting and repelling would be valuable in future studies.

The scent of offspring: chemical profiles of larvae change during development and affect parental behavior in a burying beetle

Chemical cues and signals, especially in insects, play a pivotal role in mediating interactions between individuals. Past studies have largely focused on adult semiochemicals and have neglected those of juvenile stages. Especially in the context of parental care, the larval odor might have a profound impact on parenting behavior, guiding parents in how much resources they should allocate to the different developmental stages. However, whether ontogenetic changes occur in subsocial species and whether larval-emitted scents influence parent-offspring interactions is largely unknown. Using 3 different sampling techniques, we analyzed the cuticular and VOC profile of the 3 larval instars of the burying beetle Nicrophorus vespilloides, which is known for its elaborate parental care. We found distinct differences in the cuticular and VOC profiles across the 3 larval stages. Second-instar larvae, which receive more frequent feedings from parents than the other larval stages, released greater amounts of acetophenone, methyl geranate, and octanoic acid isopropyl ester than the first and third instar. Additionally, using a newly developed bioassay with automated video tracking, we found that adding the odor of second-instar larvae to first-instar larvae increased the number of maternal feeding trips. Our results suggest that the odor produced by larvae plays an important role in mediating parent-offspring interactions. Given these findings, burying beetles might emerge as a promising candidate for identifying a potential begging pheromone.

Heterospecific eavesdropping on disturbance cues of a treefrog

Alarm signals and cues are crucial to animal survival and vary greatly across species. Eavesdropping on heterospecific alarm signals and cues can provide eavesdroppers with information about potential threats. In addition to acoustic alarm signals, evidence has accumulated that chemical alarm cues and disturbance cues can also play a role in alerting conspecifics to potential danger in adult anurans (frogs and toads). However, there is very little known about whether disturbance cues are exploited by heterospecifics. In the present study, we conducted a binary choice experiment and a prey chemical discrimination experiment, respectively, to test the responses of a sympatric anuran species (red webbed treefrogs, Rhacophorus rhodopus) and a sympatric predator species (Chinese green tree vipers, Trimeresurus stejnegeri) to disturbance odors emitted by serrate-legged small treefrogs (Kurixalus odontotarsus). In the binary choice experiment, we found that the presence of disturbance odors did not significantly trigger the avoidance behavior of R. rhodopus. In the prey chemical discrimination experiment, compared with odors from undisturbed K. odontotarsus (control odors) and odorless control, T. stejnegeri showed a significantly higher tongue-flick rate in response to disturbance odors. This result implies that disturbance odor cues of K. odontotarsus can be exploited by eavesdropping predators to detect prey. Our study provides partial evidence for heterospecific eavesdropping on disturbance cues and has an important implication for understanding heterospecific eavesdropping on chemical cues of adult anurans.