No abstract

The ability of female larvae endoparasitoids [Microplitis croceipes CRESSON : Cardiochiles nig, riceps VIERECK and Campoletis sonorensis (CARLSON)] tO distinguish between unparasitized tobacco budworm, Heliothis virescens (F.), larvae and H. virescens larvae parasitized by the egg-larval parasitoid Chelonus insularis, CRV_SSON, was determined in laboratory studies. The 3 species of larval endoparasitoid females did not appear capable of distinguishing between unparasitized and C. insularis parasitized larvae resulting in multiple parasitoidism.The results of theensuing competition between the 3 species for possession of the host-demonstrated that both C. sonorensis and M. croceipes were intrinsically superior to C. insularis. Both larva endoparasitoids destroyed the older C. insularis larvae by physically attacking the latter. The presence of C. ina:ularis larvae in the host was found to prevent the hatch of compeating C. nigriceps eggs through physiological suppression.The results show that the early attack of a host, as in the egg-larval parasitoid habit, is not necessarily advantageous.

Can. Ent. 106: 825-830 (1974) The functional response of Spalangia endius Walker was described by a linear relationship between attack rate and density of house fly pupae. S. endius searched well at higher host densities and in 72 h, appeared capable of attacking more than 80 pupae per female under laboratory conditions. The response of Muscidifurax raptor G. & S. was quadratic as poor searching ability limited this parasitoid's attack rate at high host densities. Individual parasitoid efficiency of both species was reduced by intraspecific competition when parasitoid density was increased.

In laboratory studies the effect of parasitism by the egg-larval endoparasitoid Chelonus insularis CRESSON on the resulting larvae of 2 host species, Heliothis virescens (F.) and Spodoptera ornithogalli GU~NEE) were determined by comparing daily measurements of larval weights. Growth of parasitized larvae of both host species was slower than growth of unparasitized larvae. Injections of fluids from the female parasitoid's calyx or poison gland into H. virescens eggs retarded subsequent larval growth. However, a combination of fluids from these 2 organs produced the most significant reduction in the host larval growth rate. The growth reducing factor(s) was also effective when injected into 5-day-old host larvae.