Anna Karenina as a promoter of microbial diversity in a tephritid agricultural pest (Diptera, Tephritidae)

Microbial associations are critical in determining the evolutive success of fruit fly phytophagous pests (Diptera, Tephritidae), facilitating their adaptation to suboptimal environmental conditions and to plant allelochemical defences. An important source of variation for the microbial communities of fruit flies is represented by the crop on which larvae are feeding. However, a “crop effect” is not always the main driver of microbial patterns, and it is often observed in combination with other and less obvious processes. In this work we verify if environmental stress and, by extension, changing environmental conditions, promote larval microbial diversity in Zeugodacus cucurbitae (Coquillett), a widespread, polyphagous pest. With this objective, we tested differences in the microbial profiles of wild populations from this species in an experimental setup in Eastern Central Tanzania. Our results show that ?? and ß microbial diversities change as the species gets closer to its altitudinal distribution limits and in farms where pesticides and agrochemicals are used. The microbial patterns indicate that Anna Karenina effects significantly contribute to the microbial diversity of Z. cucurbitae, and that these effects occur in stressful environmental conditions. The crop effect was comparably weaker and detected as not consistent changes across the experimental sites. We speculate that the impressive adaptive potential of polyphagous fruit flies is, at least in part, related to the Anna Karenina principle, which promotes stochastic changes in the microbial diversity of populations exposed to suboptimal environmental conditions.