The 5th instar larvae of each of the four insect species were assayed
about their capability to play as host for mass propagation of juveniles of two
beneficial entomopathogenic nematodes (EPN) species; Heterorabditis
bacteriophora and Steinernema carpocapsae in the laboratory at 25 ˚C and
65±5 % R.H. After exposure of larvae at the rate of 1000 IJs/ 5 larvae, daily
microscope inspections were carried out until larval mortality and penetration
of the new IJs out from the host larvae. Counts of the newly emerged
juveniles were carried out periodically and successively (3, 6, 9, 12, 15, 20,
25 and 30 days after starting emergence). Larvae of Galleria mellonella
manifested the shortest period from exposure to IJs until larval mortality (2
days), as opposed to 2.33 days in the case of Spodoptera frugiperda, 2.33 and
3 days after infection of Spodoptera littoralis larvae by H. bacteriophora and
S. carpocapsae IJs, respectively, and 4.33 and 2.33 days, respectively for T.
molitor larvae indicating the longest period after infection to mortality.
As for the period from the time of exposure until starting of IJs
emergence, that was the shortest (7 days) in the case of S. frugiperda infected
by either of the two EPN species and G. mellonella (by S. carpocapsae),
while this period was the longest for T. molitor infested by H. bacteriophora
and S. carpocapsae ( 12 and 14 days, respectively). After 30 days of starting
emergence out of host larvae, the highest mean of the total number of H.
bacteriophora juveniles (364767 IJs) resulted from T. molitor larvae,
followed by 284680 IJs/ S. frugiperda larvae and 259817 IJs from G.
mellonella larvae. While, in the case of S. carpocapsae; the highest number
of harvested juveniles (341790 IJs) was produced from G. mellonella larvae,
followed by 258363 IJs/ a S. frugiperda larvae and 246633 IJs/ a S. littoralis
larvae.
As a general conclusion, for mass – propagation of H. bacteriophora,
rearing on T. molitor larvae is recommended, followed by G. mellonella. On
the same target for S. carpocapsae; to obtain the highest production of
juveniles, rearing on G. mellonella larvae is the best followed by S. littoralis,
then S. frugiperda larvae.