Biological Basis for Mass Propagation of Catolaccus grandis (Hymenoptera: Pteromalidae): Effects of Parasitoid Densities and Host–Parasitoid Ratios

Abstract

We studied the effects of densities of ectoparasitoids (per liter of cage volume) and host-parasitoid ratios on the reproductive potential of parasitoid females. Ectoparasitoid, Catolaccus grandis (Burks), densities were varied from 3.8 to 37.7 females per liter volume of oviposition cages (petri dishes). Host-parasitoid ratios ranged from 0.2 to 20 3rd instars of the boll weevil, Anthonomus grandis grandis (Boheman), per parasitoid female per days. Fecundity of C. grandis females was not affected by changes in the density of female adults in oviposition cages. However, adult mortality increased when female parasitoid density exceeded 15 females per liter of cage volume. Mean percentage of parasitism of the boll weevil hosts decreased from 100 to 33% when the host-parasitoid ratio increased from 0.2 to 20.0 weevil larvae per C. grandis female per day. Parasitoid fecundity was inversely proportional to the percentage of parasitized host larvae. A higher proportion (69-75%) of fertilized eggs were oviposited when host-parasitoid ratios were between 1 and 20 host larvae per C. grandis female than when ratios were <1 host per female (40-41%). Low host-parasitoid ratios reduced the rate of reproduction in C. grandis, whereas high parasitoid densities increased intraspecific competition and parasitoid mortality. Under laboratory conditions, the most efficient host-parasitoid ratio was 5-15 host larvae per female parasitoid per day.