Abstract
Infectivity and multiplication of Steinernema feltiae (=Neoaplectana carpocapsae, str. Mexican) on the adult males, pupae, prepupae and larvae of the common cutworm, Spodoptera litura, were investigated under laboratory conditions. When the infective 3rd stage juveniles (LIIIs) of S. feltiae were inoculated either onto a moist filter paper or in 10% honey as a diet for the adults of S. litura, most of the insects died within 2 days after nematode inoculation. The number of LIIIs harvested per milligram fresh body weight in the cadavers of the adult insects was longer than that in all other developmental stages of the insect with 530 LIIIs in case of contact inoculation on filter paper and 620 in the diet inoculation. Infectivity of S. feltiae to pupae depended largely upon the age of pupae; about half the number of 1-day-old pupae were infected whereas 3-day-old pupae were not infected. In a few 1- to 2-day-old pupae, the nematodes developed to adults but were unable to emerge out of the dead pupae. Most of the infected prepupae developed to abnormally large and fragile ones which died within 2 days after the inoculation. Yields of LIIIs from these pupae were 68, 000 per insect and 280 per milligram body weight. When the newly moulted 5th instar larvae were exposed to a filter paper containing 3, 000 LIIIs per insect, infection took place within 30min. In the last 6th instar larvae, the invading LIIIs developed to adults within 2 days, yielding new LIIIs within 5 days. The peak emergence of LIIIs from the insect cadavers occurred between 9 and 14 days after the inoculation, depending on the size of the larvae. Yields of LIIIs per insect larva were positively correlated with the body weight of the larva.
