Differentiation of Developmental Pathways Results in Different Life-History Patterns between the High and Low Latitudinal Populations in the Asian Corn Borer

SIMPLE SUMMARY: The Asian corn borer, Ostrinia furnacalis (Guenée), is geographically widespread and enters a photoperiod-induced larval diapause with the gradually shortening daylengths of autumn. Here, life-history traits between non-diapausing and diapausing individuals were tested along a latitudinal gradient by rearing the larvae from six different geographical populations under their own critical daylengths to produce non-diapausing and diapausing individuals. In the non-diapausing pathway, the high-latitudinal populations had a significantly shorter larval developmental time and greater body weight than the low-latitudinal populations, whereas in the diapausing pathway, the high-latitudinal populations had longer larval developmental times and relatively smaller body weights than the low-latitudinal populations. This is the first report showing that life-history patterns of the two alternative developmental pathways were significantly different between the lower and higher latitudes. ABSTRACT: Individual insects often exhibit two alternative pathways of non-diapausing and diapausing developments. Yet, most studies have focused on the latitudinal variation in life-history traits for non-diapausing individuals. No study has examined the differences in life history traits between non-diapausing and diapausing individuals along a latitudinal gradient. We used six different geographical populations of Ostrinia furnacalis to examine the latitudinal variation in life-history traits between non-diapausing and diapausing individuals in terms of their sex ratio, larval and pupal developmental times, pupal weight, growth rate, adult weight and weight loss, and sexual size dimorphism. The results showed that latitudinal variation in life-history traits for both non-diapausing and diapausing individuals exhibited a sawtooth pattern, but the life-history pattern of the two alternative developmental pathways was significantly different between the high and low latitudes. For the non-diapausing pathway, the high-latitudinal populations showed a significantly shorter larval developmental time, higher growth rate and greater body weight than the low-latitudinal populations, suggesting countergradient variation. Conversely, in the diapausing pathway, the high-latitudinal populations had longer larval developmental times, lower growth rates and relatively smaller body weights than the low-latitudinal populations, suggesting cogradient variation. We also found that in the high-latitudinal populations, larvae in the non-diapausing pathway had shorter developmental time and higher body weight, whereas larval developmental time of the low-latitudinal populations was longer and the body weight was smaller. The relationship between larval developmental time and pupal weight was also different between the two developmental pathways. These results provide new insights into the evolution of life-history traits in this moth.