Characteristics Of The Fight Of Soybean Aphid And Its Potential For Parasitoid Dispersal

The soybean aphid, Aphis glycines Matsumura, is a pest of soybean, Glycine max (L.). The soybean aphid reduces soybean yield directly via plant feeding and indirectly through virus transmission and reduction in seed protein content. High soybean aphid densities generally affect soybean plants by reducing plant height, pod number and total yield with yield reductions reaching 50%. The soybean aphid has recently invaded North America and Canada in 2000, where it is currently the most important insect pest of soybeans. Winged aphids (alates) engage in flight to colonize new plants, fields or habitats, and at critical times migrate between different host plants, aphids engage in (active) short-distance flight but also exploit weather patterns mainly for (passive) long-distance migration. Hymenopterous parasitoids are of great significance for natural control of aphid populations. The dispersal of parasitoids with host flight is tightly associated with host aphids. Aphid parasitoids take advantage of host flight for dispersal which would be contributed to biological control of the soybean aphid. In our research, we first studied the active flight potential of A. glycines under a range of environmental conditions and the trade-offs between flight and fecundity in the soybean aphid using an aphid flight mill to aid forecasting and management protocols for A. glycines at the landscape level, then we detected the host alates post-parasitization flight and the development of parasitoids in alate aphids. Our research has implications for classical biological control of the soybean aphid. The main results were summarized as follows.Aphids that were 12-24 h old exhibited the strongest flight behavior, with average flight durations of 3.3-4.1h, which represented flight distances of 4.6-5.1 km. After the age of 72 h, A. glycines flight performance rapidly declined. The optimum temperature range for flight was 16-28oC, while optimum relative humidity was 60%-90%. Our findings show that A. glycines posseses a fairly strong active flight aptitude (ability and inclination) and point to the possibility of flight initiation under a broad range of environmental conditions. Fecundity, longevity and reproductive periods of 12h old A. glycines alates which had engaged in >2.5 km long flights were significantly lower than those of <0.5 km individuals. The offspring of alates with flight experiences of >1.5 km also had lower fecundity than those produced by individuals which had engaged in flights <1.5km. Our results are therefore consistent both with direct trade-offs between flight and fecundity and a trade-off between flight and fecundity via maternal effects.Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3th and 4th instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids that had been parasitized as 4th-instar alatoid nymphs 24 h or 48 h prior to testing was similar to that of un-parasitized alates of identical age. However, flight performance declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72h and 96h prior to testing. Flight performance of aphids that had been parasitized as alate adults for 24h was not significantly different from un-parasitized alates of respective ages. Parasitoid larval and pupal development time and percent mummification did not differ between treatments in which aphids had flown over varying distances.We investigated the effect parasitism by the parasitoid Binodoxys communis on flight behavior of both the summer population soybean aphid and fall gynoparae. In summer population, flight distance of alate aphids that had been parasitized for 24 or 48 h did not differ significantly from unparasitized alates of the same ages. However, flight duration sharply declined for alates that had been parasitized for 72h and 96h. Larval and mummy development time, parasitoid emergence rate of passenger wasps did not differ between treatments in which the aphid host had flown over differing distances. In gynoparae, flight performance of gynoparae aphids that had been parasitized as 4th-instar alatoid nymphs 7d prior to testing was similar to that of un-parasitized alates of identical age.These results have the potential to aid forecasting and management protocols for A. glycines at the landscape level and help evaluating the dispersal efficiency and overwinter host of parasitoid. Our results have implications for natural biological control of A. glycines.