New published research has found systematic cannibalism between larvae of Isodontia harmandi . This result was established during a five year research period (2010-2015) in which 495 nests have been examined.
Brood cannibalism is possible because the species builds communal brood chambers in which multiple eggs are deposited.
The authors point at possible prey scarcity as the cause for a female to decide to deposit more eggs in the chamber, which would make this a purposeful decision with the aim for the larvae to commit to cannibalism.
Remarkable since she could equally decide to lay less eggs so the one larva would have sufficient food.
This behaviour is not seen in I. mexicana , in the Netherlands classified as an introduced species and also the only representative from this genus, since it does not construct communal brood chambers .
PLOS ONE source article
References1 Nederlands Soortenregister
2 Imasaki Y, Endo T (2022) Brood reduction caused by sibling cannibalism in Isodontia harmandi (Hymenoptera: Sphecidae), a solitary wasp species building communal brood cells. PLOS ONE 17(5): e0267958. https://doi.org/10.1371/journal.pone.0267958
3 O’Neill, K. M., & O’Neill, R. P. (2003). Sex Allocation, Nests, and Prey in the Grass-Carrying Wasp Isodontia mexicana (Saussure) (Hymenoptera: Sphecidae). Journal of the Kansas Entomological Society, 76(3), 447–454. http://www.jstor.org/stable/25086133