Every Friday mid-May through mid-October, a staff member at Kellogg Biological Station (KBS) drives to a tall, narrow pipe on the Long-term Ecological Research (LTER) main experiment site, opens a small door at the base of the tower and extracts a bottle filled with liquid and a cornucopia of insects.The little critters, victims of a strong suction at the top of the pole as they fly by, are shipped to the University of Illinois where David J. Voegtlin and Doris Lagos, experts in the identification of aphids, determine the species of aphids in the bottle and the number of each.
His particular target in the KBS bottle is an aphid species that loves soybeans and not only can harm soybeans by sucking out juices but can also transmit a lethal virus.
Voegtlin and his team are particularly active each summer, analyzing samples collected from 35 similar insect vacuums that are part of the 8-state North Central Regional Soybean Aphid Suction Trap Network.
Information about the total number of aphids captured are collated and returned to each station where it becomes part of the long-term aphid-monitoring project.
Insect tower sampling allows research teams to determine what insects are present, when they are present and how many there are, he said, noting that sampling can serve as an "early warning system." "It's an unbiased sampler," Voegtlin said. "The towers suck down all insects that happen to fly over the top of the tube. We don't try to attract insects. We catch insects that are migrating into the area."
Voegtlin is an insect specialist whose primary focus is the taxonomy and biology of aphids.
Aphids are among the most destructive insect pests on cultivated plants in temperate zones. Worldwide there are some 4,400 species, about 250 of which are serious pests for agriculture and forestry. The tiny, soft-bodied insects migrate long distances by taking to the air and riding with the wind until they literally spot the plant they favor, said Christine (Christie) Bahlai, a research associate in Michigan State University's Department of Entomology and KBS LTER investigator.
"They sense the crop host, probably mostly by color, and settle," she said.
Bahlai, whose research is based in part on samples collected at the KBS LTER site from 2005 to 2009, said that the number of aphids collected by the KBS vacuum varies significantly from year to year. In 2005, for example, there were more than 6,600 soybean aphids collected at KBS. In 2013 the number was just under 100.
"There were outbreaks in 2001, 2003 and 2005," she said. "And while the outbreaks tend to occur in two-year cycles in the eastern portion of their range, we are seeing fewer aphids now than in the past. We aren't having many problems with aphids so there's not much to research."
Soybean aphids were first seen in the United States in 1999 and have spread since, Bahlai said, rapidly became the nation’s most significant threat to soybean production. And while hotter summers do favor aphid growth, there is not enough data to determine if climate change is affecting aphid spread and population.
Soybean aphids typically have four molts each generation, she said, and are flightless until the last. "Usually by the third molt you see tiny wing buds. By the last molt they have fully-formed wings and take off and ride by the wind. Quite often crowding induces them to fly."
Once settled in they reproduce asexually—no need for a male—and their numbers grow. Bahlai said that male aphids are produced near the end of the growing season while on soybeans, but fertilization occurs after the insects fly to where they over-winter.
Voegtlin said that the aphid-trapping project was started in 2001 in Illinois and spread to the other states in 2005, when collections were started at KBS. His team counts 17 different pest aphid species, each of which prefers different host plants, including corn, wheat, peas, alfalfa and potatoes as well as soybeans.
Some farmers plant seeds that are treated to be more resistant to aphid infestations. The seed treatment provides some level of protection for about 60 days.
In Europe, researchers in the Rothamsted Insect Survey have been collecting insect pests in suction traps since 1964.
Bahlai notes that long-term records such as this provide the data needed to make predictions about the effects of invasive insects and unpredictable insect outbreaks on crop and other ecosystems. She and Lagos and their colleagues are currently seeking funding to keep this network—and long-term data set—going.