Soybean Aphid Fall Flight - Destination: Buckthorn

Eileen Cullen, Extension Entomologist

Soybean aphids have settled in for surviving winter in Wisconsin and the north central region. Each September and October, winged  male and female soybean aphids fly to buckthorn. After the fall flight, females lay eggs that overwinter on the woody host and hatch in early spring. Aphids will feed on emerging buckthorn leaves in May, before winged aphids migrate to soybeans in June.

Both soybean aphid and common buckthorn, Rhamnus cathartica, its main overwintering host in the U.S., are invasive species introduced from Asia. The aphid can also overwinter on Alder-leaved buckthorn, Rhamnus alnifolia, a Buckthorn species native to the northern United States.

Regional Soybean Aphid Suction Trap Network …

Wisconsin soybean growers and agricultural consultants have teamed up with University of Wisconsin Extension to monitor soybean aphid flights from June through October each year. Thanks to this partnership, Wisconsin now has 7 locations state-wide reporting to a Regional Soybean Aphid Suction Trap Network. 

Fall flight activity is important because it may indicate the size, and potentially success, of the overwintering soybean aphid population. Years with high soybean aphid overwintering flights to buckthorn may be followed by heavy soybean aphid populations in soybeans the next growing season. There is some evidence for the predictive potential of suction trap data from Illinois in previous years.

Suction traps are used to montior soybean aphid flight activity
in Wisconsin and throughout the north cenral region.

Wisconsin suction traps are located in the following counties: Walworth (Sharon), Columbia (Arlington), Lancaster (Lancaster), Waushara (Hancock), Eau Claire (Eau Claire), Outagamie (Seymour) and Langlade (Antigo). Grant support from the Wisconsin Soybean Marketing Board  and North Central Soybean Research Program helped to install the WI traps, provide aphid identification services, and timely reporting to Wisconsin soybean producers.

A Regional Soybean Aphid Suction Trap Network website posts weekly winged soybean aphid counts for Wisconsin and nine surrounding states.

www.ncipmc.org/traps/

Home page screen view of the North Central IPM Center

Regional Soybean Aphid Suction Trap Network website.

Trap captures June through August represent soybean aphids flying between soybean fields (dispersal flights).  It is the September-October flight numbers that entomologists track to understand what kind of overwintering flight has occurred in the Midwest.

Table 1. 2006 Soybean aphid suction trap captures by state and month. 

Sept.-Oct. column represents the overwintering flight to buckthorn.¹

State (sites)	Jun	Jul	Aug	Sept.- Oct.
WI (7)	1	221	843	213
MN (5)	4	409	497	376
IL (9)	0	10	142	1762
IA (4)	0	21	358	532
IN (6)	0	3	28	8322
MI (5)	0	1	7	209

¹Values in table display total soybean aphids captured each month from all sites per state.

Suction traps are a means to track aphid overwintering flights, and are much easier and less time consuming than searching buckthorn plants for soybean aphid eggs. 2006 completed the 2^nd  suction trapping season in Wisconsin, with 7 traps operational. Multi-year data statewide, and regionally in cooperation with other states will help us assess the long-term value of suction traps as a predictive tool between seasons.

In 2006, Wisconsin, Minnesota, and Michigan had the lowest overwintering flight numbers. Illinois and particularly Indiana, registered heavy overwintering flights. Fall flights varied in intensity over the region with potentially high sources of overwintering aphids in IL and IN.

Soybean aphid populations in 2007 will depend on several factors.  Predators, such as the Asian lady beetle, can reduce aphid populations on buckthorn in fall before aphids deposit eggs; and again in spring after eggs hatch. Eggs that are laid must survive the winter. Heavy rains or sub-freezing temperatures in early spring can kill young aphid colonies on buckthorn in spring.