Seasonal and geographical variation in diapause and cold hardiness of the Asian corn borer, Ostrinia furnacalis.

Asian corn borer, Ostrinia furnacalis (Guenée), is a key corn pest in the Asian-Western Pacific countries. It overwinters as full-grown larvae in plant stalks or in a spun-silk covering located in the plant debris in the temperate regions of China. Supercooling point (SCP) and survival rate after low sub-zero temperature treatment were assessed for field-collected populations in the laboratory using a cool bath with a 1°C/min cooling rate until -40°C. Mean SCPs were varied among geographical populations, with a significant decline from -22.7°C of Haikou, the multivoltine tropical population in the south, to -28.5°C of Gongzhuling, the univoltine temperate population in the northeast of China. In addition, there was more than 1°C difference in SCP between Gongzhuling univoltine and bivoltine populations that were from the same geographic origin. Mean SCPs of the Guangzhou population fluctuated over the year, with significantly lower SCPs in winter than in other seasons, which correlated with a significantly higher proportion of diapausing larvae in winter than in other seasons. Over 41% of overwintering larvae from the northeast population could withstand to be supercooled for a few minutes to the low sub-zero temperature of -40°C, but only 6.7% of their southern counterparts did so. The findings from this study suggest that O. furnacalis mostly takes advantage of freeze avoidance as diapausing larvae for overwintering in the southern region, whereas it exhibits freeze tolerance in diapause in the northeastern region.

[Effects of elevated atmospheric CO2 on plant, herbivorous insect, and its natural enemy: a review].

Since the industrial revolution, the huge consumption of fossil fuels and unduly destruction of natural habitats by human activities have led to the ever-increasing concentration of atmospheric CO2. To study the adaptation mechanisms of plant, herbivorous insect, and its natural enemy within agricultural ecosystems to the elevated atmospheric CO2 concentration is of significance in deciphering the damage pattern of agricultural pest occurrence and controlling the pest occurrence and in mitigating the CO2 emission from agricultural ecosystems. This paper reviewed the research progress on the effects of elevated atmospheric CO2 on the host plant, herbivorous insect, and its natural enemy in agro-ecosystem, with the focuses on the improvement of related research methods, the variation patterns of host plant primary and secondary metabolites induced by elevated atmospheric CO2, the effects of the elevated CO2 on the growth and development, population density, and behaviors of herbivorous insect, and the biology and predation and/or parasitism rates of natural enemy. The future research frontiers in this research area were also discussed.

Impact of wheat-mung bean intercropping on English grain aphid (Hemiptera: Aphididae) populations and its natural enemy.

The effects of intercropping wheat, Triticum aestivum L., with mung bean, Vigna radiate L., on the populations of English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), and its natural enemies were evaluated by field and laboratory experiments. The population densities of aphids and their natural enemies were evaluated in the intercropped field against different row ratio combinations of wheat-mung bean. Results showed that wheat-mung bean intercropping caused a drop in aphid densities, and the ratio 12 wheat: 4 mung bean brought about the largest drop (> 8%). In addition, the population densities of coccinellids (ladybirds) and parasitoids and the species diversity of all the natural enemies of aphid were higher in the intercropped field than in the field planted only with wheat. However, intercropping did not influence the community indices (evenness and index of dominance concentration) of the natural enemies. Y-tube olfactometer bioassays were carried out in the laboratory to test whether odor blends of host and nonhost plants affect the host selection of S. avenae. Bioassays indicated that both apterous and alate aphids significantly preferred host plant odor over odor blends of host and intercropped species. Hence, the olfactory-based host location of aphids in the field might be affected by intercropping. The intercropping experiment clearly showed that increased crop species diversity suppresses aphid population growth and preserves the population of natural enemies of aphids. Our results also provide support for the "resource concentration hypothesis" and the "enemies hypothesis".