Insects and Survival: A Review of Primary and Secondary Defense Strategies

Selective pressure has driven the evolution of defensive strategies in insects against their natural enemies. These strategies are classified into primary and secondary defenses, which are further subdivided into behavioral, morphological, and chemical categories based on the mechanisms they employ. This review aimed to synthesize insect defense mechanisms from the literature published over three decades (1992–2023), describing and analyzing their efficiency, effects, and relationship with the life history of these organisms. Reports of primary and secondary defenses were obtained for insects across 22 and 20 orders, respectively. Defensive secretions, crypsis, and aposematism were the most reported primary defenses, while toxin release, fighting, and escape were the most frequently reported secondary defenses. Chemical defenses affect insect life history and, although most frequently reported, are not the most widespread across orders. Crypsis and escape, belonging to the morphological and behavioral subdivisions, respectively, are the most common primary and secondary defenses across insect orders. Understanding these mechanisms provides essential insights for biodiversity conservation and sustainable pest management.