Spontaneous and induced activity of Heterorhabditis megidis infective juveniles during storage

Abstract

Summary -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 (AT 50 ) 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.

Survival, starvation, and activity in Heterorhabditis megidis (Nematoda: Heterorhabditidae)

“…The diVerences between UK211 and HF85 in survival, lipid utilization, and size are stable: UK211 is consistently larger, survives longer, and uses its reserves more slowly than HF85 (present study; Fitters and GriYn, 2004;Fitters et al, 1997;GriYn et al, 1994;Hass et al, 2001), despite the fact that both of these isolates had been in culture for at least a decade by the time of these experiments.…”

“…The Estonian isolate, EU17 stands out in surviving longer and utilizing its reserves at a much slower rate than all other isolates. This exceptional position of EU17 was not maintained in another study (Fitters and GriYn, 2004), which included three of the eight isolates used here. In that study, EU17 did not diVer from UK211 in these parameters though both of these isolates maintained their superiority over HF85.…”

“…That locomotory activity contributed measurably to the depletion of reserves of H. megidis, is supported by the Wnding that there was a steep drop in reserves during the Wrst week of storage (Fig. 2), and this corresponds to the period when IJs are highly active (Fitters and GriYn, 2004). With longer storage, reserves were depleted more slowly (Fig.…”

“…With longer storage, reserves were depleted more slowly (Fig. 2), and an increasing proportion of IJs is inactive unless stimulated (Fitters and GriYn, 2004). However, as well as declining motility, age-related changes in metabolism (Croll and Mathews, 1973;Houthoofd et al, 2002) could also have contributed to the decline in rate of utilization of reserves by the IJs.…”

Substrates for storing entomopathogenic nematodes (Rhabditida: Steinernematidae, Heterorhabditidae)

“…(Piracicaba, Braz. ), v.67, n.3, p.342-347, May/June 2010 crobial composition of the storage medium (Dempsey and Griffin, 2002;Fitters and Griffin, 2004). Consequently, investigating the parameters that influence EPN survival under storage is an important aspect to be considered for their release in the field in biological control programs (Brown and Gaugler, 1997).…”