Evaluation of transgenic Bt corn for resistance to the Asian corn borer (Lepidoptera: Pyralidae)

The Asian corn borer, Ostrinia furnacalis (Guenée), is the most important insect pest on corn in China. Bt transgenic corn provides a new tool for Asian corn borer control. Monsanto's YieldGard Bt transgenic corn expressing Cry1Ab protein, and a non-Bt control, were evaluated in Beijing. Laboratory bioassays were carried out by exposing neonates to an agar-free diet containing Bt corn whorl leaves, tassels, and anthers, or by exposing neonates directly to fresh silk and pollen. These are the tissues initially attacked by neonates in the field. All of these tissues, with the exception of pollen, contained sufficient insecticidal protein to kill > or = 95% of larvae within 7 d. Surviving larvae had also not grown beyond first instar and weighed < or = 0.1 mg. Although larvae feeding on Bt corn pollen were significantly smaller than those on non-Bt corn pollen, there was no significant difference in mortality. Field trials were also conducted with artificial infestations of Asian corn borer at mid whorl, late whorl, and silking stages. Damage ratings and number of larvae surviving per plant indicated that Bt corn was highly resistant to Asian corn borer. Therefore, YieldGard offers the potential for season-long protection against first- and second-generation Asian corn borer.     

Evaluation of spatial and temporal patterns of insect damage and aflatoxin level in the pre-harvest corn fields to improve management tactics

Spatial and temporal patterns of insect damage in relation to aflatoxin contamination in a corn field with plants of uniform genetic background are not well understood. After previous examination of spatial patterns of insect damage and aflatoxin in pre-harvest corn fields, we further examined both spatial and temporal patterns of cob- and kernel- feeding insect damage, and aflatoxin level with two samplings at pre-harvest in 2008 and 2009. The feeding damage by each of the ear/kernel-feeding insects （i.e., corn earworm/fall armyworm damage on the silk/cob, and discoloration of corn kernels by stink bugs） and maize weevil population were assessed at each grid point with five ears. Sampling data showed a field edge effect in both insect damage and aflatoxin contamination in both years. Maize weevils tended toward an aggregated distribution more frequently than either corn earworm or stink bug damage in both years. The frequency of detecting aggregated distribution for aflatoxin level was less than any of the insect damage assessments. Stink bug damage and maize weevil number were more closely associated with aflatoxin level than was corn earworm damage. In addition, the indices of spatial-temporal association （χ） demonstrated that the number of maize weevils was associated between the first （4 weeks pre-harvest） and second （1 week pre-harvest） samplings in both years on all fields. In contrast, corn earworm damage between the first and second samplings from the field on the Belflower Farm, and aflatoxin level and corn earworm damage from the field on the Lang Farm were dissociated in 2009.     

双斑长跗萤叶甲越冬卵在玉米田的空间分布型

为明确双斑长跗萤叶甲越冬卵的空间分布型,2011年10月采用分层随机抽样法在山西省晋中市的玉米田对土壤中的越冬卵进行调查.通过频次分布检验、聚集度指标的测定、改进的Iwao m*-m回归分析法和Taylor幂法则对越冬卵在土壤中的空间分布型进行了分析,并对聚集均数(λ)进行检验,分析越冬卵聚集的原因.结果表明:双斑长跗萤叶甲越冬卵在土壤中的理论分布型符合负二项分布,各项聚集度指标均满足C＞1、CA＞0、I＞0、k＞0、m*/m＞1,空间分布图式在低密度下为聚集分布,基本成分为单个个体,个体间相互排斥.基本成分的相对聚集度随越冬卵种群密度而变化的速率为3.52m-15.61.种群密度越大,相对聚集度的变化速率也越大,而且聚集的程度随着卵密度的增大而增高.聚集均数(λ)的测定表明,聚集是成虫的产卵习性和田间植被的生长情况、土壤性质、温湿度等环境因子综合作用的结果.双斑长跗萤叶甲成虫主要在近土表的土壤中产卵,在距土表15 cm以上的土壤中,有94.2％的越冬卵分布在距土表0-10 cm的土层中,其中以距土表2-5 cm的土层中的卵量最多,平均每个样点有卵25.56粒,占总数的64.7％,显著高于其他深度土层的卵量.     

Impact of heat waves on egg survival and biological performance across life stages in the Asian corn borer

One of the many extreme events as a result of climate change is the frequent appearance of extraordinarily daily high temperatures that can directly drive an insect's adaptive response. Insects have complex life cycles that may uncouple temperature's effects in one stage from the physiology in the next. In this study we focused on the Asian corn borer (ACB), Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae), one of the most important pests of maize (corn) in Asia, investigated the consequences of eggs exposed to ecologically relevant heat shock regimes, simulating heat waves at extreme high temperature. This consisted of five 90-min heat treatments separated by two degrees that ranged from 37 to 45°C for three consecutive days compared to a constant temperature of 25°C. Temperature that triggered mortality was between 39 and 41°C. Egg hatching significantly declined when temperature was 41°C or higher. There was no egg hatching at 45°C. Developmental times were significantly prolonged and the larval growth rate became slower in treatments of 41 and 43°C. There were no significant differences in pupal mass, fecundity, and sex ratio among treatments. Life table parameters showed significant adverse effects at treatments of 41 and 43°C. Depending on the fitness response of the ACB, environmental heat waves can be classified into three categories based on temperature criteria, i.e., adaptable (35–39°C), critical (39–45°C), and fatal (≥45°C). The findings of the present study will serve as an important reference for forecasting the population dynamics of the ACB.