Group joining behaviours in the entomopathogenic nematode Steinernema glaseri

Aggregations of foraging animals are key aspects of their ecology, driving spatial patterns, resource access, and successful resource exploitation. Entomopathogenic/insect parasitic nematodes demonstrate aggregated population structures. However, there are gaps in our understanding of how different behaviours affect aggregation. To understand joining behaviour as a mechanism of aggregation, we examined the group movement and joining behaviour of the EPN species, Steinernema glaseri, in conspecific (S. glaseri) and heterospecific (S. carpocapsae and S. feltiae) assemblages. We assessed group movement of S. glaseri using a glass olfactometer where nematodes were added to the central hub and allowed to disperse into six arms towards cues at the ends. We measured movement in the absence of external cues, when host cues were present but uniform, and in response to both con- and heterospecific entomopathogenic nematodes. S. glaseri dispersed in a highly aggregated fashion both in the presence and absence of host cues. When conspecific nematodes were present in the olfactometer ends, S. glaseri readily moved towards and joined conspecific groups, particularly if those conspecifics had experienced host contact 48 h previously. When heterospecific nematodes were present in the ends, S. glaseri only appeared to preferentially join groups of S. feltiae with prior host contact. S. glaseri exhibited no propensity to join groups of S. carpocapsae regardless of prior host contact. Findings demonstrate context-dependent joining behaviours that may underlie aggregation in EPNs. These behaviours may lead to more effective mass attack and regulate interspecific competition among these insect parasites.