Stuck in the Caterpillars' Web: A Half-Century of Biocontrol Research and Application on Gregarious Lepidopteran Pests in Europe

Unraveling multiple layers of collective behavior outside the well-known isopteran and hymenopteran societies was a tall order for the scientific community, especially in the case of gregarious juveniles in the order Lepidoptera. Often protected with a solid silk shelter, devoid of reproductive division of labor or conventional forms of parental care, caterpillar aggregations have rarely been considered in terms of economic importance. Of over 60 European communal species, 24 can be associated with voracious feeding habits, and thus be irruptive or pestilential, depending on the extent and severity. This review retrieves 59 cases of biocontrol against Hyphantria cunea (Drury), Euproctis chrysorrhoea (L.), Malacosoma neustria (L.), Thaumetopoea pityocampa (Denis and Schiffermuller), T. processionea (L.) and Yponomeuta malinellus (Zeller) and classifies them in predefined research and application subcategories. The percentage-wise distribution of the utilized or explored biocontrol agents was projected at 35.59% in favor of parasitoids and predators. Falling between fundamental and applicative disciplines, biocontrol, especially in its early days, built a global reputation of being underreported. To provide guidance for future research regarding the group, the functional trait-based concept used in this study is complemented with preliminary outcome assessment.