Below are some hot-off-the-press items from this week’s soybean entomology meeting in Baton Rouge.

The entomologists from southern and Midwest states get together annually to share research findings, and I’ve listed some of the more interesting tidbits here.

SOYBEAN APHID

• Fall suction trap survey: The fall flight of SBA in 2008 was the largest recorded in the regional suction trap network. However, no one has reported finding eggs on buckthorn. The only explanation people can come up with is fungal infection (in other words, beneficial fungi infecting and killing the egg-laying aphids on the buckthorn). Fungal killed aphids were found at several sites in the midwest. We will survey in the spring to see if there are populations on buckthorn.
• Threshold in narrow rows: Univ of MN compared the SBA injury level and threshold in 30 inch rows vs 10 inch narrow-rows. Across 2 years at 3 locations, they found no difference. In other words, the 250 threshold works in both 30 inch or drilled beans.
• SBA and SCN: In Wisconsin, researchers examined the performance of SBA on soybean cyst nematode infested plants (in other words, do aphids do better or worse on SCN plants?). Thus far, they haven’t found a difference, but the work is continuing.
• SBA & spud viruses: We’ve known for several years that SBA can transmit potato virus Y, an important disease in seed potato. But it is now proven that SBA can also transmit potato leafroll virus. This is surprising, because PLRV is a circulative virus that must churn around inside an insect, moving to the salivary glands to be injected into a new plant. This usually means that only aphids that live directly on potato (green peach aphid, potato aphid) transmit this disease, but now SBA is proven to as well.
• SBA host plant resistance: There are now 3 different host plant resistance sources. The genes are called ‘RAG’ for the phrase Resistance to Aphis Glycines.
• Rag1 was the first resistance type identified by Univ of Illinois. It was a single dominant gene found in the MG7 variety Dowling. Varieties with Rag1 resistance will be available in Canada in 2009 and in the US likely in 2010. Aphid resistance in Rag1 is not perfect – multiple researchers report finding aphids feeding on Rag1 plants (and even reports of ‘failure’ of Rag1 resistance = hundreds of aphids per plant), so there is a certain % of the aphid population that can overcome Rag1 resistance. However, even slowing aphid reproduction down may be important in the field because natural enemies may be able to do a better job controlling the population.
• Rag2 is another single dominant gene, discovered by Rouf Mian, a breeder at Ohio State. This gene functions differently from Rag1, and will be another source of resistance. Research is being done to see if aphids can overcome this gene as well. I don’t know the commercial status of Rag2.
• Rag3 and Rag4 are two recessive genes discovered by Dechun Wang at MSU. The genes function together to produce an extremely high level of resistance (one researcher at the meeting termed it “better than an insecticide application”). Dechun’s genes are harder to work with because there are two genes on separate chromosomes and they are not dominant. However, the resistance looks fantastic in multiple trials across the midwest. The genes have been licensed to commercial companies and varieties are expected a few years from now.

STINK BUGS

• Some people call stink bugs ‘giant aphids’, because they both suck plant sap. Stink bug populations in the south are increasing and becoming quite devastating in soy production. There are multiple species in the south, including a new species (red-banded stink bug) moving north through Louisiana. Stink bug feeding damages beans in the pod, increase pod diseases, and is one cause of green stem. Southern researchers report that growers now spray 5 – 7 TIMES for stink bugs – in some cases this makes soy production barely possible given the $$ spent on spraying. Thankfully we do not have stink bug numbers to such an extent in the midwest, but we are watching the northern progress of some of these species.

HONEY BEES

• New honey bee law in Iowa: Applicators cannot make an application of a pesticide toxic to bees within 1 mile of a registered apiary, between the hours of 8am and 6pm. Apparently an apiary under this law can be even a single hive.

SOURCE: Dr. Christina DiFonzo, Field Crops Entomology Program, Michigan State University