UC San Diego

Habitat loss and fragmentation collectively are a leading cause of biodiversity decline, including in a variety of insect groups. However, the effect of habitat fragmentation on solitary Aculeate wasps is unclear. To contrast Aculeate wasp populations in areas affected and unaffected by fragmentation, we used bowl traps to sample these wasps in scrub fragments (small, isolated patches of habitat) and scrub reserves (large expanses of habitat) in San Diego County in 2015, 2016, and 2022. No significant differences were observed between reserves and fragments in the total number of wasps captured or in the number of Crabronid (family Crabronidae) wasps sampled in either of the three years. However, in 2016, reserves had significantly more wasp genera, more Crabronid genera, and more Pompilid (family Pompilidae) individuals compared to fragments. Due to there being no significant difference in any category in at least two of the three sampling years, it appears that Aculeate wasps are resistant to fragmentation-driven changes, although this varies by year and by family. Further investigation using different sampling methods, greater number of years, and a closer examination of specific families and genera could shed light on this relationship.