Whether Macdunnoughia crassisigna (Lepidoptera: Noctuidae) is a Long-Distance Migrant?

Abstract

Macdunnoughia crassisigna (Warren) is an important polyphagous pest of bean crops and cruciferous vegetables. Whether this species is a migrant, and if so, what pattern of seasonal migration it exhibits in northern China remains unknown. The combination of searchlight trapping, ovarian dissection, and carbon isotope analysis on a small island in the center of the Bohai Strait during 2003–2013, provided direct evidence that both male and female M. crassisigna moths migrate at least 40–60 km across the sea. There was considerable annually and monthly variation in the number of M. crassisigna caught in the searchlight trap, with the vast majority (80.40 ± 4.84 %) was trapped in the summer. The mean time from the earliest trapping within a year was 143 ± 10 days from 2003 to 2013, with the shortest time span of 54 days in 2003 and the longest of 173 days in 2012. Carbon isotope analysis showed that 5.82 ± 0.92 % to 17.88 ± 8.10 % of the tested M. crassisigna moths originated from C4 plants from May to September 2010–2013, which provides additional evidence that this species is a migrant because there are no C4 plants on this island. The vast majority of the trapped females were virgins (86.29 ± 1.97 % to 89.29 ± 1.67 %) with little or no ovarian development (level 1–2, 81.06 ± 4.98 % to 87.34 ± 2.76 %) from May to September 2009–2013, as suggests that the onset of migration this species exhibits is initiated mainly by sexually immature individuals, which is termed the ‘oogenesis-flight syndrome’. Given that large numbers of adult M. crassisigna were captured while flying up to 500 m above sea level at a site with no local populations, the findings indicate that M. crassisigna is a long-distance migrant, and the pattern of seasonal migration this species exhibits is a regular ecological behavior in northern China. Such results highlight a new route for developing sound forecasting systems of M. crassisigna.