Endo- or ecto-parasitism with the cluster fly, Pollenia dasypoda Portochisky (Diptera: Calliphoridae), based on the diameter of its host body, the earthworm Allolobophora caligonosa (Sav.)

Abstract

Parasitism with the cluster fly, Pollenia dasypoda Portochisky (Diptera: Calliphoridae), in relation to its host, the earthworm Allolobophora caligonosa (Sav.), was studied at Giza region, Egypt. Also, different biological parameters of the parasitoid were studied. Natural parasitism rate during March 2019 ranged between 4 and 10% per 50 earthworms. In 6 samples (300 earthworms), the total rate of parasitism was 12.66%. Experimental parasitism by placing the newly hatched larvae (L1) of P. dasypoda, directly on the bodies of their host worms, A. caligonosa, resulted to 100% parasitism in all replicates. An interesting phenomenon by larvae of the last instar (L3) of P. dasypoda appeared during the study. This parasitoid is known as an endo-parasitoid on the earthworms, where the third instar larvae (L3) complete their development inside the same parasitized earthworm. But under laboratory conditions of the present study, few individuals of L3 became ecto-parasitoids on the parasitized earthworm. The reason behind this behavior was the diameter of the host (earthworm). Experimentally, the L1 was placed on young earthworm, and when reaching the L3, its body diameter became larger than that of its host. To avoid the pressure of the host body around L3, it moves backward from the host body keeping its head with mouthparts inserted in the same location of initial parasitism, continuing feeding for 4–5 days as ecto-parasitoid, until fully developed. Then, it leaves the host and turns into a pupa adjacent to the corpus of its mostly dead host earthworm.