Intra– and Interspecific Competition Among Two Parasitoids of the Rice Weevil (Coleoptera: Curculionidae)

Abstract

We studied intra- and interspecific competition among 2 parasitoids [ Anisopteromalus calandrae (Howard) and Lariophagus distinguendus (Forster) (Hymenoptera: Pteromalidae)], which attack the rice weevil, Sitophilus oryZae (L.). As the intraspecific density of the parasitoids increased, the search rate per female and rate of population increase of A. calandrae decreased curvilinearly, suggesting a type of contest-like intraspecific competition. The other parasitoid, L. distinguendus , seemed to exhibit a type of scramble-like intraspecific competition; as long as the number of hosts available was not severely limiting, the search rate and rate of population increase of the parasitoid were not related to the intraspecific density of parasitoids. Statistics estimated for the interspecific competition model suggested that A. calandrae was the dominant competitor and could displace L. distinguendus . However, under conditions of interspecific competition, the 2 species of parasitoids coexisted until the rice weevil population was completely suppressed. This apparent coexistence seemed to be possible because of the differences in the type of intraspecific competition exhibited by the 2 parasitoids.