Vertically Transmitted Gut Bacteria and Nutrition Influence the Immunity and Fitness of Bactrocera dorsalis Larvae

Abstract

Symbiotic bacterial communities that colonize the digestive tract of tephritid fruit flies interact with nutrient intake to improve the flies' fitness and immunity. Some bacterial species consistently inhabit the tephritid guts and are transmitted to the next generation vertically. These species contribute significantly to some aspects of their host's physiology. In the current study, we examined the role of four vertically transmitted bacteria (Citrobacter, Enterobacter, Klebsiella, and Providencia) on the fitness parameters and immunity of Bactrocera dorsalis larvae that were fed a nutritionally manipulated diet. For this purpose, eggs were collected from axenic, gnotobiotic, and symbiotic adult flies, and larvae were reared on four types of diets in which carbohydrate and/or protein contents were reduced and then compared with larvae raised on a control diet. The diet and bacterial interactions significantly affected the fitness and immunity of B. dorsalis. Larvae of axenic flies grew slower and displayed weaker immune-based responses (PO activity, antibacterial activity, survival) than larvae of gnotobiotic and symbiotic flies. Overall, larvae reared on the low-protein diet grew slower than those reared on the control or low-carbohydrate diets. Survival, PO activity, and antibacterial activity were significantly lower in the hemolymph of larvae reared on low-protein diets. Our results also revealed that the levels of hemolymph protein, glucose, trehalose, and triglyceride in larvae from axenic flies were significantly lower than those in larvae of the symbiotic group after they fed on most of the tested diets. These results strongly infer that diet and vertically transmitted bacteria are both essential contributors to the fitness and immunity of B. dorsalis.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

“…There may be an association between the symbiont acquisition or transmission and the nature of the interactions between insects and symbionts. It is usual for female germline transmission to occur vertically through the female germline as with primary mutualists, for example, those present in aphids and weevils ( Caspi-Fluger et al, 2012 ; Douglas, 2015 ; Hassan et al, 2020 ). It is common for environmental microorganisms to be transmitted across internal organs, some of which can form secondary symbioses without specialized organs.…”

Comparative Transcriptomic Analyses of Antibiotic-Treated and Normally Reared Bactrocera dorsalis Reveals a Possible Gut Self-Immunity Mechanism

“…Reports have also shown that folic acid can be synthesized by the intestinal microflora in animals (Hanson and Gregory, 2011). These reports provide a wealth of genetic information for our (Hassan et al, 2020). However, insects have an effective gut defense system that maintains self-immunity, thereby preserving the balance among microorganisms in the gut and stabilizing the diversity in gut symbiotic bacteria.…”

“…Immunity is important for insects. Both diet and vertically transmitted bacteria can influence the fitness and immunity of B. dorsalis ( Hassan et al, 2020 ). However, insects have an effective gut defense system that maintains self-immunity, thereby preserving the balance among microorganisms in the gut and stabilizing the diversity in gut symbiotic bacteria.…”

Differential Responses of Ceratitis Capitata to Infection by the Entomopathogenic Fungus Purpureocillium Lilacinum.

“…Therefore, nutrition is essential to pathogens resistance in insects 42,43,44 . Gomulski et al 45 , suggested that the abundance of immune gene transcripts might be related to the nature of the food sources within C. capitata.…”