Thermoregulation in gregarious dipteran larvae: evidence of species‐specific temperature selection

Abstract

Due to the ephemeral nature of carcasses they grow on, necrophagous blowfly larvae should minimize the time spent on the cadaver. This could be achieved by moving to high-temperature areas. On that basis, we theorized that larvae placed in a heterogeneous thermal environment would move to the higher temperature that speed up their development. This study was designed to (1) test the ability of necrophagous larvae to orientate in a heterogeneous thermal environment, and (2) compare the temperatures selected by the larvae of three common blowfly species: Lucilia sericata (Meigen), Calliphora vomitoria (L.) and Calliphora vicina (Robineau-Desvoidy). For this purpose, we designed a setup we named Thermograde. It consists of a food-supplied linear thermal gradient that allows larvae to move, feed, and grow in close-to-real conditions, and to choose to stay at a given temperature. For each species and replication, 80 young third instars were placed on the thermal gradient. The location of larvae was observed after 19 h, with fifteen replications per species. The larvae of each species formed aggregations that were always located at the same temperatures, which were highly species-specific: 33.3 AE 1.52°C for L. sericata, 29.6 AE 1.63°C for C. vomitoria, and 22.4 AE 1.55°C for C. vicina. According to the literature, these value allows a fast development of the larvae, but not to reach the maximum development rate. As control experiments clearly demonstrate that larval distribution was not due to differences in food quality, we hypothesized that the local temperature selection by larvae may result from a trade-off between development quality and duration. Indeed, temperature controls not only the development rate of the larvae, but also the quality of their growth and survival rate. Finally, results raise questions regarding the way larvae moved on the gradient and located their preferential temperature.

To eat or get heat: Behavioral trade‐offs between thermoregulation and feeding in gregarious necrophagous larvae

“…However, our experiments showed only a slight attractive/retentive effect of conspecific‐marked food. According to this result, the persistence of larval aggregation far above the 34 °C preferred temperature (Aubernon et al ., ) cannot be fully explained by an aggregation signal from conspecifics. However, as observed in several studies, necrophagous larval aggregates are self‐organized systems based on local communication and interaction among individuals (Boulay et al ., ).…”

“…This trade‐off is particularly important because of the gregarious behavior of larvae, which can lead to larval masses in which thousands of individuals gather. According to previous developmental studies (Grassberger & Reiter, ) and behavioral observations (Aubernon et al ., ), larval masses temperatures can rise far above the critical thermal maximum of L. sericata larvae. But although behavioral thermal regulation inside larval masses is often postulated, no experimental data support this hypothesis (Charabidze et al ., ; Rivers et al ., ).…”

Les larves de diptères nécrophages en entomologie médico-légale : une histoire de température

“…Une étude [22], fondée sur l'utilisation d'un dispositif innovant nommé le Thermograde 3 , a révélé la sélec-tion préférentielle d'une température. Cette analyse, qui a porté sur les larves de troisième stade de trois espèces majeures d'intérêt forensique (Lucilia sericata, Calliphora vomitoria 4 et Calliphora vicina 5 ), montre en 2 L'effet Allee est un phénomène de dépendance à la densité des populations.…”

“…La tempéra-ture qu'elles rencontrent au sein même de la nourriture qu'elles prélèvent a un impact sur leur comportement [26]. En effet, en utilisant un logiciel de suivi vidéo, l'analyse du comportement d'une larve de L. sericata soumise à de la nourriture chauffée à 25 °C (expérience témoin), à 34 °C (température préférentielle de l'espèce [22]) ou à 38 °C (température létale pour l'espèce [8]) a montré que les larves pouvaient se nourrir quelle que soit la température de la nourriture fournie. Cependant, dans les conditions de températures élevées, le temps total passé dans la zone nutritive et la durée de chaque passage des larves sont diminués.…”

Predators, Parasites and Heterospecific Aggregations in Chrysomeline Larvae

“…; Aubernon et al. ) and improve immune responses (Catalán et al. ), ultimately improving survival (Wade & Breden ; Ronnås et al.…”