Pollen contamination in seed mixture increases the dominance of resistance to Bt maize in Spodoptera frugiperda (Lepidoptera: Noctuidae).

BACKGROUND: Seed mixture, also called 'RIB', has been used to provide refuge populations for delaying insect resistance. Pollen contamination in RIB could result in refuge kernels of non-Bt maize expressing variable Bt proteins. Data are lacking regarding the impact of pollen contamination on evolution of resistance for ear-feeding insects. Here, we used Spodoptera frugiperda and Cry1F-maize as a model to examine if pollen contamination in RIB increases the dominance of insect resistance. RESULTS: Pollen contamination caused >66% refuge kernels in 5:95% (non-Bt:Bt) and 20:80% RIBs to express Cry1F protein. Survival at adult stage on pure non-Bt ears was similar (54.4-63.3%) among Cry1F-susceptible (SS), Cry1F-resistant (RR) and Cry1F-heterozygous (RS) S. frugiperda. On Bt ears, survival was similar between SS and RS (0.0-1.7%), but it was significantly less than that of RR (59.2%). On the two RIB refuge ears, survival at adult stage for RS (42.3% in 5:95% RIB; 50.0% in 20:80% RIB) was significantly higher than for SS (8.7% in 5:95% RIB; 10.0% in 20:80% RIB). CONCLUSION: The results suggest that pollen contamination in RIB could increase the dominance of resistance for ear-feeding insects by significantly reducing susceptible refuge populations and supporting higher survival of heterozygotes relative to homozygous susceptible insects. © 2017 Society of Chemical Industry.

Effect of temperature on the occurrence and distribution of colorado potato beetle (Coleoptera: Chrysomelidae) in China.

Colorado potato beetle, Leptinotarsa decemlineata (Say), is the most destructive pest of potato in many countries of the world. It first invaded China from Kazakhstan in 1990s and now is a major pest of potato in many areas of Xinjiang Uygur Autonomous Region (Xinjiang). The objective of this study was to determine the effect of temperature on the spread of Colorado potato beetle in China after its invasion. Cold temperature in winter (December) and high temperature in summer (July) were analyzed in accordance with the absence and presence of Colorado potato beetle in Xinjiang. The boundary between the absence and presence of Colorado potato beetle in Xinjiang nearly coincided with the -8°C isotherm of monthly mean minimum temperature in winter. The stress of the low temperature in winter for Colorado potato beetle basically disappeared in the southeastern Hexi Corridor in Gansu Province of China, suggesting that the Hexi Corridor is the best channel to prevent any long-distance invasions of Colorado potato beetle into the Central Plains region. However, in Turpan City in northeastern Xinjiang, the extremely hot weather in the summer prevents the local colonization of Colorado potato beetle. Furthermore, according to our monitoring, high temperature in summer also limited Colorado potato beetle to diffuse eastward through Turpan. Results of this study suggest that it is essential to strengthen inspection and quarantine measures to prevent any artificial transmissions of Colorado potato beetle spreading eastward and thus to ensure the sustainable production of potato and other Solanaceae crops in northwest regions of China.