TRITROPHIC INTERACTIONS IN SORGHUM, MIDGE (STENODIPLOSIS-SORGHICOLA) AND ITS PARASITOID (APROSTOCETUS SPP.)

Studies on tritrophic interactions involving sorghum genotypes, midge (Stenodiplosis sorghicola) and the predominant parasitoids (Aprostocet us spp.) at ICRISAT Asia Center were conducted using three midge resis tant (ICSV 745, ICSV 89058 and IS 10712) and three susceptible (Swarna , CSH 9 and ICSV 112) genotypes during the post-rainy (1992/93) and ra iny (1993) seasons. A. coimbatorensis, the predominant parasitoid duri ng post-rainy season, preferred mid-late midge larvae for parasitizati on, while A. gala, which was predominant during the rainy season, pref erred early-mid larval stages. Variations in the preference of A. coim batorensis and A. gala for the developmental stage of their host larva e indicate good prospects for the biological control of sorghum midge populations. There were significant differences in parasitization leve l of midge by Aprostocetus spp. between resistant and susceptible sorg hum genotypes, and season. Higher parasitization was observed on susce ptible genotypes than on resistant ones during both post-rainy and rai ny seasons. However, the level of parasitization was greater in post-r ainy than in rainy seasons. There was also evidence of higher midge in festation in rainy than in post-rainy seasons. Susceptible genotypes a ttracted more parasitoids because of high levels of midge infestations . Low parasitoid density in midge resistant sorghum under glasshouse a nd field conditions was associated with low midge infestations in thes e genotypes. However, parasitoids were always associated with their ho st in spite of low midge densities in resistant genotypes. The present study revealed that the interaction between host plant resistance and parasitoids of sorghum midge would thus be synergistic and complement ary and could result in successful integration of these two important pest management tactics. (C) 1998 Elsevier Science Ltd. AII rights res erved.