Update:
We surveyed commercial soybean fields in the northern third of Iowa and found strong evidence of insecticide resistant aphids. This evidence included populations spreading and increasing beyond the what was measured before an insecticide was sprayed. This is remarkable because insecticides have performed very well, reducing populations and preventing yield loss after they are applied. We are using molecular markers to determine if the aphids collected both before and after the use of an insecticide have mutations associated with insecticide resistance. We anticipate that the frequency of these mutations will increase after the application. This is very worrisome as this will increase the likelihood of these mutations spreading.
We also learned that despite the increase in aphid spread and population after the insecticides were applied, the populations were very low, at least an order of magnitude below what is considered a threshold to spray insecticide. This is somewhat comforting, but highlights a larger issue. Farmers may be using insecticide unnecessarily, applying them when they are not needed to prevent yield loss from soybean aphids. By using insecticides in this way, they are eroding the value of insecticides. Even though the populations are too low to cause yield loss, they are still responding to the insecticide, with the resistance evolving and spreading amongst the survivors.
These data will be used in the years to come to demonstrate how insecticide use in soybeans can erode their value. This will be done across multiple platforms, including twitter, podcasts and the many farmer meetings conducted through ISU extension and outreach.
View uploaded report 
We surveyed commercial soybean fields in the northern third of Iowa and found evidence of insecticide resistant aphids. This result is important for two reasons. The first is that the soybean aphid populations across Iowa were very low, including the fields we visited. Some of the 22 fields we visited had no aphids, even the fields with the most aphids had populations below what is required to reduce soybean yield (< 250 aphids per plant on average). A subset of these fields were sprayed with insecticide. Either the farmer was very risk-adverse or was practicing a preventative approach (i.e. a 'prevent-defense') to avoid possible outbreaks later in the season. This brings up the second reason our result is important is that even with this low density of aphids, we found evidence of insecticide resistance in the population. This was most noticeable after the insecticides were applied. When we returned to these fields at least 7 days after an insecticide was applied, not only had the percentage of plants infested with aphids increased, but so too had the average number of aphids on them. This is the response we would see if the aphids were resistant to the insecticide.We are using molecular markers to determine if the aphids collected both before and after the use of an insecticide have mutations associated with insecticide resistance. We anticipate that the frequency of these mutations will increase after the application. This is very worrisome as this will increase the likelihood of these mutations spreading.
Even though the populations of aphids increased after insecticides were applied, they were too low to reduce soybean yield. So the farmers did not suffer immediately from these resistant aphids. But this is very troubling. Insect susceptibility to insecticide is a natural resources that can be eroded with continued insecticide use. Farmers may be using insecticide unnecessarily, applying them when they are not needed to prevent yield loss from soybean aphids. By using insecticides in this way, they are eroding the value of insecticides. Even though the populations are too low to cause yield loss, they are still responding to the insecticide, with the resistance evolving and spreading amongst the survivors.
Going forward, we will share these results with farmers. We hope that these results will show farmers the potential consequences of insecticide use that is not immediately necessary. Furthermore, we will couple our molecular data to determine if that data can more rapidly determine the presence of aphid resistant soybeans than bioassays with living aphids.