Yellow Peach Moth (YPM), Conogethes punctiferalis (Guenée), is one of the most destructive maize pests in the Huang-Huai-Hai summer maize region of China. Transgenic Bacillus thuringiensis (Bt) maize provides an effective means to control this insect pest in field trials. However, the establishment of Bt resistance to target pests is endangering the continued success of Bt crops. To use Bt maize against YPM, the baseline susceptibility of the local populations in the targeted areas needs to be verified. Diet-overlay bioassay results showed that all the fourteen YPM populations in China are highly susceptible to Cry1Ab. The LC50 values ranged from 0.35 to 2.38 ng/cm2 over the two years of the collection, and the difference between the most susceptible and most tolerant populations was sevenfold. The upper limit of the LC99 estimates of six pooled populations produced >99% larval mortality for representative eight populations collected in 2020 and was designated as diagnostic concentrations for monitoring susceptibility in YPM populations in China. Hence, we evaluated the laboratory selection of resistance in YPM to Cry1Ab using the diet-overlay bioassay method. Although the resistant ratio was generally low, YPM potentially could evolve resistance to Cry1Ab. The potential developmentof resistance by target pests points out the necessity to implement resistance management strategies for delaying the establishment of pest resistance to Bt crops.

Field trials based on manual infestation of the Asian corn borer (ACB) (Ostrinia furnacalis (Guenée)) and Fusarium verticillioides (Nirenberg) atomization were conducted on four maize hybrids to investigate the relationship between ACB infestation and F. verticillioides infection, yield loss and fumonisins contamination in maize. Analysis of fumonisin B1 and B2 was carried out using an LC-MS/MS system. In this study, manual ACB infestation significantly promoted F. verticillioides infection (both symptomatic and symptomless) and grain fumonisins level. Ear rot incidence and severity, symptomless kernel infection and fumonisins contamination were significantly correlated to each other and to ACB damage severity. Manual ACB infestation increased fumonisin level from 580 to 4418 µg/kg in 2018, 6059 to 10681 µg/kg in 2019 spring-sown maize (2019A), and 2042 to 5060 µg/kg in 2019 summer-sown maize (2019B), while the concentration threshold of European Union (EU) is 4000 µg/kg. In spring of 2019, fumonisins level in kernels from untreated controls exceeded threshold of EU. Significant negative correlation between ACB damage and ear weight were observed. Regarding yield, significant negative correlation between ACB damage and ear weight were observed in three seasons. These results indicated that ACB infestation can lead to severe quality degradation and yield loss of maize. Kernel fumonisin level may exceed concentration threshold of EU in certain conditions, threatening health of livestock and human. Measures should be taken to reduce ACB infestation to ensure food and feed security.

Field experiments were conducted to evaluate the role of two corn borers, Asian corn borer (ACB), Ostrinia furnacalis and Yellow peach moth (YPM), Conogethes punctiferalis, on Fusarium verticillioides infection using green fluorescent protein (GFP) as a marker. Effects of insect injury, manual injury and insecticide application on fumonisin production also were assessed. In this study, 3rd instars of ACB and YPM significantly increased GFP-tagged F. verticillioides infection compared to the control, regardless of fungal inoculation method. Besides acquiring F. verticillioides spores from leaf surfaces and transmitting them to ears, larvae of the ACB and YPM also injure maize ears, which allows F. verticillioides from leaves or silk to infect ears more easily. This suggests ACB and YPM larvae are vectors of F. verticillioides, which can increase the occurrence of ear rot. Manual injuries significantly increased GFP-tagged F. verticillioides infection in ears, while an effective insect control significantly reduced F. verticillioides infections of ears. Insecticide control of borers also significantly reduced fumonisins content in kernels. Larval infestations significantly increased fumonisins in kernels to levels higher or very close to EU threshold (4000 μg kg-1). Significant and high correlations among corn borer attack, F. verticillioides severity and kernel fumonisins levels were discovered, confirming the important role of ACB and YPM activity on F. verticillioides infection and kernel fumonisins production.