EA - Research summary: brain cell counts in Black Soldier Flies (Hermetia illucens; Diptera: Stratiomyidae) by Rachel Norman

Link to original articleWelcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Research summary: brain cell counts in Black Soldier Flies (Hermetia illucens; Diptera: Stratiomyidae), published by Rachel Norman on August 15, 2022 on The Effective Altruism Forum. Summary An organism’s number of brain cells (e.g., neural processing power) may be a relevant proxy in assessing its likelihood of being sentient and, consequently, its capacity for welfare. In addition, quantitative proxies like brain cell numbers allow for more objective comparisons of moral weight across species, or across developmental stages within the same species. Isotropic fractionation (IF), a technique recently pioneered for application in insects by Godfrey et al. 2021, allows for insect brain cells to be quickly and reliably counted. IF can be used to determine the number of brain cells in insects, such as the black soldier fly (BSF; Hermetia illucens). Billions of BSFs are farmed annually across the globe, mainly to be used as animal feed, and the industry is growing. Understanding the likelihood of sentience in BSFs is important due to the massive scale of this new agricultural sector. My study co-authors and I determined the number of brain cells in adult male and female BSFs as well as L1, L4, and L6 stage larvae. As shown in the paper (preprint here), larvae produced a 9-fold increase in brain cell numbers across larval development; pupation caused a 16-fold increase in brain cell numbers for adults. Adult BSFs had an average of ~331,000 brain cells; males and females differed in the number of cells in their brains, due to differences in the optic lobes (peripheral processing regions responsible for the input of visual information). In the central brain, BSF adults had ~42,000 CB cells irrespective of sex. These data allow for BSF (at multiple developmental stages) to be included in interspecific welfare comparisons that use brain cells as a relevant measure of capacity for welfare. Caveats This post assumes sentience in insects is possible, but does not attempt to assess how probable it is based on the data gathered. In addition, it assumes cognitive capacity may be considered a proxy for sentience. Brain cell counts by themselves provide limited evidence for cognitive capacity, and should be used in conjunction with other behavioral and anatomical data. With insects there is often very little data on these other features (recently reviewed here); brain cell counts may represent an initial foray, then, into understanding a species’ cognitive complexity. Thus, this research does not assess cognitive sophistication, nor the capacity for welfare in BSF, but may still be of interest to those working to understand BSF sentience. This post is not meant to examine the utility, or pros/cons, of brain cell numbers as a proxy for cognitive capacity, sentience, or moral weight. The data reported herein are for total brain cell numbers, which includes non-neuronal cell populations. Data from other Diptera (flies, mosquitoes, etc.) suggest neurons may make up ~90% of all brain cells (Raji & Potter 2021). Introduction Between 200 and 300 billion individual black soldier flies (BSFs) are estimated to be farmed annually to be used as animal feed, and the industry is expected to grow (Rowe 2020). The vast majority of farmed BSFs are killed as larvae. Larvae have excellent biomass conversion abilities (Cicková et al. 2015, Lalander et al. 2015), and exchange any waste products they may consume into nutrition for livestock and exotic pets (among other products; Lee et al. 2021, Hopkins et al. 2021, de Souza Vilela et al. 2021). BSFs belong to the order Diptera, family Stratiomyidae; they are in the same order as the model organism, Drosophila melanogaster (though D. melanogaster belongs to a different family, Drosophilidae). BSFs are native to the Neotropics, but due to globalization have...