The aphidophagous gall midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), a dominant natural enemy of aphids, has been used as a biological control agent in many countries to control aphids in greenhouses. As developmental arrest in diapause lowers the effectiveness of natural enemies, we studied the effect of photoperiod and temperature on the incidence of diapause in a Japanese strain of A. aphidimyza by examining diapause induction under different day-length conditions in the laboratory. The critical day length for diapause induction was determined to be 12.7 h at 20°C. Diapause incidence was completely prevented at 30°C even though the photoperiod used was 11L13D. We also examined diapause induction under changing temperature conditions while maintaining the critical day length (12.7L11.3D). Diapause incidence was 100% in both field and greenhouse conditions under alternating temperatures of 20/16 or 25/16°C while the critical day length of 12.7 h was maintained. The Japanese strain of A. aphidimyza was sensitive to diapause entry from the first to the third noncocooned instar larval stages. Its eggs do not seem to be sensitive to diapause induction. Our results suggest that constant short-day conditions for at least four days are needed to induce diapause in the Japanese strain of A. aphidimyza.
Abstract:In the mass rearing of Euscepes postfasciatus using artificial diets, a method for estimating the number of eggs is essential for monitoring egg-collection efficiency and controlling egg-seeding density on the diets. To develop a simple method, we first analyzed the relationship between the volumes of eggs aspirated into a 1-or 2-ml measuring pipette and the number of eggs in it. A significant difference in the pattern of increase in egg number, along with the increase of volume, was found between the two pipette types. Linear and quadratic regressions fitted well for the 1-and 2-ml pipette data, respectively (R 2 Ͼ0.97). To extend the egg-number estimation to a larger quantity of eggs, we performed similar analyses using a 5-ml measuring cylinder. Here, the number of eggs contained was determined using the above measuring pipettes and regressions. A linear regression of the estimated number of eggs on volume fitted well (R 2 ϭ0.99). The results show that the number of E. postfasciatus eggs can be estimated precisely using measuring pipettes or cylinders. This study also showed that the pattern of increase in egg number differs depending on the measuring equipment, which should be considered for establishing egg-number estimation methods for other insects.
We examined the effects of powdered plant material as an ingredient of the artificial diet for egg collection, the dehydration method for preparing plant material (freeze or thermal dry), and timing of mixing the plant material in diet preparation procedure (pre-or post-heating) on the number of eggs obtained, adult survival rate, and egg hatchability of Euscepes postfasciatus, a serious pest of sweet potato (Ipomoea batatas). The type of plant material did not significantly affect the adult survival and hatchability but markedly affected the number of eggs obtained. Diets with the leaves and vines of the host plants of E. postfasciatus (sweet potato and a wild host, Ipomoea pes-caprae) realized twice the number of eggs than diets with the storage root of sweet potato, indicating an advantage of the former parts of Ipomoea plants as an ingredient of the diet for egg collection. The drying method for the plant parts and timing of mixing the plant material did not significantly affect the number of eggs obtained and other parameters, suggesting that some unknown factor(s) of leaves and vines inducing good oviposition of E. postfascuatus may be stable to heat treatment.
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