Spontaneous and induced activity of Heterorhabditis megidis infective juveniles during storage

Abstract

Abstract Infective juveniles (IJ) of three Heterorhabditis megidis isolates, HF85, EU17 and UK211, were stored in water at 20°C for up to 10 weeks. At 2-week intervals, activity, infectivity, energy reserves and survival were measured. There was no difference between the three isolates in infectivity, which increased significantly over the first 2 weeks and declined gradually thereafter. IJ became inactive during storage. Out of storage, the highest activity was recorded in week 0: nearly all IJ were active within the first minute of observation and remained active for the 20-min observation period. With increasing storage time, an increasing proportion of IJ were inactive in the first minute, reaching 83–96% by week 6. The time taken by 50% of the IJ to become active (AT50) initially increased with nematode age, reaching a maximum of 3–7 min in week 4 or 6 (depending on isolate) but subsequently declined to 2–4 min in week 10. By the time the IJ were becoming more readily activated in weeks 6–8, 75% of the lipid reserves had been depleted, and IJ had started to die. This greater propensity to become active with age may represent a switch to risk-taking behaviour in the face of impending starvation.