Aggregative oviposition varies with density in processionary moths—Implications for insect outbreak propensity

In gregarious insects, groups commonly originate from females laying eggs in masses and feeding are established as soon larvae hatch. Some group-living insect species may aggregate beyond the individual parent level, such that offspring two or more egg develop within a common resource. Here we show aggregative oviposition can vary with population density at possibly be an important factor outbreak dynamics of phytophagous insects. We analysed data respect to mass aggregation for pine processionary moths, Thaumetopoea pinivora (in Sweden 2005–2019) T. pityocampa Spain 1973–1991). Both lay their feed groups. During study periods, both varied by least order magnitude. The showed strikingly similar patterns aggregation. Egg were overdispersed high density, few trees showing load masses. Our suggest explaining previously documented higher propensity outbreaks insects clusters, compared those eggs.