Development of the entomopathogenic nematode Heterorhabditis megidis strain NLH-E 87.3 in Galleria mellonella

Abstract

Increasing densities of Heterorhabditis megidis strain NLH-E 87.3 infective juveniles (IJ) affected invasion, reproduction, length and time to first emergence of the nematodes in larvae of the greater wax moth, Galleria mellonella. Although the number of nematodes that invaded the host increased with increasing dose, percentage of invasion declined. The number of progeny produced per host initially increased with dose. The highest production of IJ per cadaver was reached at a dose of 300 IJ per host, at that dose 62 ± 3.4 IJ were established per cadaver. Production decreased again significantly at higher densities. The smallest IJ were produced at a dose of 1000 IJ per host and the largest at a dose of 300 IJ per host. Time to first emergence of juveniles was generally shorter when the number of IJ inoculated was large (300-3000 IJ/host).Des densités croissantes de juvéniles infestants (IJ) d'Heterorhabditis megidis souche NLH-E 87.3 ont affecté la pénétration, la reproduction, la longueur du corps et la date de la première émergence des nématodes des larves de Galleria mellonella. Bien que le nombre de nématodes ayant pénétré dans l'hôte ait augmenté avec l'inoculum, le pourcentage de pénétration a décru. L'importance de la descendance produite par hôte a initialement augmenté avec l'inoculum. La production la plus forte d'IJ par cadavre a été atteinte à un taux d'inoculum de 300 IJ par hôte; à ce taux d'inoculum, 62 ± 3.4 IJ par cadavre avaient pénétré. La production d'IJ a de nouveau diminué significativement aux taux d'inoculum plus élevés. Les IJ les plus petits ont été obtenus au taux d'inoculum de 1000 IJ par hôte. Le temps écoulé jusqu'à la première sortie des juvéniles hors de l'insecte a été généralement plus court lorsque le taux d'inoculum était élevé (300-3000 IJ/hôte).

The effect of initial dose on the recovery and final yields of Heterorhabditis megidis (Rhabditida: Heterorhabditidae) in larvae of the great wax moth, Galleria mellonella

“…According to Mannion and Jansson (1993), Heterorhabditis nematodes maintain their invasive abilities for several days, and the higher the initial nematode concentration, the greater the percentage of larvae entering host's body and initiating further development. Quite a different tendency is observed by Boff et al (2000), who find that an increase of initial dose results in a decrease of the percentage of nematodes initiating further development in G. mellonella larvae. They obtain the highest recovery (38.3%) at the smallest initial dose (10 IJs) and the lowest recovery (16%) with 1000 IJs.…”

“…No effect of the initial dose on the production of invasive larvae is also demonstrated by Shapiro-Ilan and Gaugler (2002) for H. bacteriophora and S. carpocapsae, by Flanders et al (1996) for H. bacteriophora and by Elawad et al (1999) for S. abbasi. A strong effect of a high concentration of nematodes (3000 IJs) on final yields is, however, shown by Boff et al (2000). A slight increase of the number of invasive larvae that are observed with increasing dosages remains until the application of a dose of 300 IJs.…”

“…Intense competition decreases the health of parasitic nematodes, their reproductive abilities and, consequently, the number of offspring. Based on studies and observations of Boff et al (2000), it could be concluded that H. megidis are more resistant to overcrowding than other species of EPNs, such as H. bacteriophora. The final efficiencies found for H. megidis were higher than those noted by Boff et al (2000), despite the fact that both experiments were performed under the same thermal conditions (25°C).…”

“…Based on studies and observations of Boff et al (2000), it could be concluded that H. megidis are more resistant to overcrowding than other species of EPNs, such as H. bacteriophora. The final efficiencies found for H. megidis were higher than those noted by Boff et al (2000), despite the fact that both experiments were performed under the same thermal conditions (25°C). Mason and Hominick (1995) found that nematode production in the body of G. mellonella larvae is higher at 15°C and 20°C than at 25°C.…”

“…These results suggest that the most effective initial dose of H. megidis grown in the body of G. mellonella larvae at 25°C is 50 IJs. Boff et al (2000) calculate the coefficient of reproduction, i.e. the ratio of final yields to the number of nematodes that managed to penetrate the insect's hemocoel, which was also negatively correlated with the size of initial dose.…”