Abstract:

To understand the parasitism characteristics of tachinid parasitoids, Exorista civilis Rondani and Nemorilla maculosa Meigen (Diptera: Tachinidae) on the population of the beet webworm Loxostege sticticalis L. (Lepidoptera: Pyralidae), the number and position of the tachinid eggs and the parasitism rate in various instars of L. sticticalis were investigated in a field population in Kangbao, Hebei province. The relationship between the tachinid parasitoid survival and the host instars and the number and position of tachinid eggs on the host larvae was also analyzed. The results showed that the parasitism rate on the 5th instar host larvae by the tachinid flies was the highest. The number of tachinid eggs deposited on the 5th instar larva by these two tachinid flies varied from 1 to 8 eggs per host larva, with one egg per host larva dominant (45%), and followed by two eggs per host larva (33.6%). However, only one tachinid maggot could survive in a host. The tachinid eggs located more on head and thorax than on abdomen. Compared with the dorsal and abdominal sides of the host larvae, the lateral side was the most favorite side attacked by the tachinids. The survival rate of the tachinid progeny was highly related to their egg number on the host larva. Only 66.7% of the host larvae with one tachinid egg each could produce a mature maggot，while 100% of the host larvae with more than two tachinid eggs each could produce a mature maggot.

Key words: Exorista civilis, Nemorilla maculosa, Loxostege sticticalis, parasitic character, survival rate