Stress in dipteran insects mass-reared for sterile insect technique applications

Stress may be viewed as the disturbance of homeostasis of an organism. Stress may arise from the external or internal environment of living organisms and plays a significant role in the fight or flight responses of animals. An organism's potential to resist stress is determined by its ability to mount up an effective response against the stress factors. Therefore, stress-induced biomolecules are useful indicators of a well-functioning immune system. While the interactions between stress and immunity are well-studied in vertebrate and plant systems, they are insufficiently documented among invertebrates, including dipteran insects that are mass-reared for sterile insect technique (SIT) applications. Generally, mass-reared insects may experience a variety of stress factors, which may affect various biological traits, including fecundity, weight of the progeny, adult emergence rates, flight propensity, mating ability, and their competitiveness with wild conspecifics. Many of these biological traits determine the costs and success of SIT programs. It is imperative to understand how stress impacts the quality of the reared insects and their biological traits, as well as the insect's defense responses to stress factors, to maintain robust and healthy colonies for successful release programs in SIT. Here, we review and discuss the sources and responses to biotic and abiotic stress in general in insects, while prioritizing literature on dipteran insects for SIT programs. We also coalesce genes and pathways that are modulated during stress and may be used as indicators to diagnose stress with the final aim to improve insect health in mass-rearing colonies.