Infective Juveniles of Entomopathogenic Nematodes (Steinernema and Heterorhabditis) Secrete Ascarosides and Respond to Interspecific Dispersal Signals

Ascarosides are a modular series of signalling molecules that are widely conserved in nematodes where they function as pheromones with both behavioural and developmental effects. Here we show that the developmentally arrested infective juvenile (IJ) stage of entomopathogenic nematodes (EPN) secrete ascarosides into the surrounding medium. The exometabolome of Steinernema carpocapsae and Heterorhabditis megidis was examined at 0, 1, 7 and 21 days of storage. The concentration of several ascarosides (ascr#11, ascr#9, ascr#12, ascr#1 and ascr#14 for both species, plus ascr#10 for H. megidis) showed a progressive increase over this period, while the concentration of longer chain ascarosides increased up to day 7, with an apparent decline thereafter. Ascr #9 was the main ascaroside produced by both species. Similar ascarosides were found over a 7-day period for Steinernema longicaudum and S. feltiae. Ascaroside blends have previously been shown to promote nematode dispersal. S. carpocapsae and H. megidis IJs were stored for up to 12 weeks and assayed at intervals. IJs where exometabolome was allowed to accumulate showed higher dispersal rates than those where water was changed frequently, indicating that IJ exometabolome maintained high dispersal. Infectivity was not affected. IJ exometabolome accumulated over 7 days promoted dispersal of freshly harvested IJs, both of their own and other EPN species. Similarly, extracts of nematode-infected cadavers promoted dispersal of con- and heterospecific IJs. Thus, IJs are encouraged to disperse from a source cadaver or from other crowded conditions by public information cues, a finding that may have application in enhancing biocontrol. However, the complexity of the ascaroside blend produced by IJs suggests that it may have ecological functions other than dispersal.