Insect rearing protocols in forensic entomology: Benefits from collective rearing of larvae in a carrion beetle Necrodes littoralis L. (Silphidae)

Abstract

Forensic entomologists frequently use a developmental method to estimate a post-mortem interval (PMI). Such estimates are based usually on the blow fly larvae or puparia. Data on their development is obtained by rearing them in colonies. In the case of beetles, which can be also useful for PMI estimation, development data is frequently collected by rearing them individually. However, some carrion beetles are gregarious, for instance, Necrodes littoralis (Linnaeus, 1758) (Silphidae). We compared mortality, rate of development and body size of emerged adult beetles reared individually and in aggregations. Mortality was much higher for beetles reared individually, particularly at low temperatures. The rearing protocol affected the time of immature development and the size of adult insects. Individually reared specimens developed much longer at 16°C, whereas at 20°C and 26°C development times of individually reared beetles were slightly shorter. Significant differences in the body size were observed only at 16°C; beetles that developed in aggregations were larger at this temperature. These findings demonstrate that aggregating is particularly beneficial for larvae of N. littoralis at low temperatures, where it largely reduces mortality and facilitates growth. Moreover, these results indicate that in forensic entomology the protocol of individual rearing is unsuitable for gregarious beetles, as it produces reference developmental data of low quality.

The Impact of Diet and Photoperiodism on the Life History ofThanatophilus sinuatus(Coleoptera: Silphidae)

“…However, the main factor could be the different rearing methodologies applied; in Jakubec et al (2019), larvae were separated individually from L1 to minimize competition, which may have prolonged the development and caused the high mortality. This was similarly indicated in Gruszka and Matuszewski (2021) work on Necrodes littoralis (Linnaeus, 1758). The possible effects of heat production and cooperative feeding are beneficial when aggregating in a group, as noticed by Gruszka et al (2020) and Matuszewski and Mądra-Bielewicz (2021), yet this can perhaps be true only for L1 and L2 Thanatophilus larvae, as the L3 larvae are more independent.…”

“…Rearing also delivers developmental information under regulated conditions that may further improve future TOC and PMI estimations (Byrd and Tomberlin 2019b). Therefore, it is important to create laboratory rearing protocols and methods to gain a clearer understanding of the main biotic and abiotic factors that may affect the development, and further enhance the quality of the developmental data obtained (Ridgeway et al 2014, Gruszka and Matuszewski 2021, Jakubec et al 2021a, b; Matuszewski 2021).…”

Temperature models of development for Necrodes littoralis L. (Coleoptera: Silphidae), a carrion beetle of forensic importance in the Palearctic region

“…It amounted to 30% 58 , whereas only 3.75% of the beetles died in 22 °C in the current study. Probably the higher mortality reported by Dekeirsschieter resulted from individual rearing of larvae, since mortality rate of individually reared larvae of N littoralis was found to be higher compared to the larvae that were reared in aggregations 61 . However, other effects might have been important, as well.…”

Calibrating insect age at eclosion by size in a gregarious carrion beetle Thanatophilus sinuatus (Staphylinidae: Silphinae)

“…While aggregated, they pool the enzymes and other exudates to optimise this process (Charabidze et al, 2021;Rivers et al, 2011). Benefits from the collective exodigestion, that is, shorter development and lower mortality were experimentally demonstrated for the aggregations of larval blow flies (Scanvion et al, 2018) and were also postulated for Necrodes beetles (Gruszka & Matuszewski, 2021). Similar benefits probably result from the aggregations of T. sinuatus larvae; when in a group these larvae exodigest and feed at an optimal, fast rate that shortens their development.…”