ISSUE 15 September 17, 2009
SOYBEAN APHIDS MOVING BACK TO BUCKTHORN
Soybean aphids have started to move out of soybean fields and back to buckthorn, their overwintering host. This is a sure sign of fall for an entomologist. The North Central Region Suction Trap Network will be monitoring fall flight of soybean aphid back to its overwintering host, buckthorn. Visit the suction trap network website for updated data September through October 2009
When out finishing soybean aphid counts in the field last week, it was easy to find aphids killed by entomopathogens (insect-killing fungi). The heavy dews and recent rains are good conditions for fungal growth and infection. Natural enemies, such as Asian multicolored lady beetle (Harmonia axyridis) and Syrphid fly larvae, are also easy to find and helped keep populations of soybean aphids below the economic threshold this year. Asian multicolored lady beetles (Fig. 1) are easy to identify by the M or W-mark behind the head. Their color varies from black to yellow to red with zero to many black spots (16 spots are common). Syrphid fly larvae (Fig. 2) are usually green or brown, about 12 mm long and slug-like in appearance with a pointed head.
Figure 1. Asian multicolored lady beetle.
(Photo by S. Bauer, USDA-ARS Image gallery,
Figure 2. Larva of Syriphid fly eating aphids.
(Photo by C. Moorehead, Bugwood.org)
SAP BEETLES OBSERVED IN FIELD CORN
Sap beetles (Coleoptera: Nitidulidae) have been observed feeding on corn ears and silks (Fig. 3). These small ( inch), black beetles with four orange or yellow spots on the wing covers are sap beetles, also known as picnic beetles (Fig. 4). It is not unusual to find sap beetles feeding in corn ear tips late in the season. Sap beetles are secondary invaders of injured corn ears or stalks that are damaged by some means, often another insect, like corn borer. Sap beetle may play a role in spreading molds (rot diseases), which also contribute to ear damage. Regardless of the reason for infesting corn ears, the injury caused by sap beetles is usually negligible and non-economic, so control actions are not warranted. Once the corn reaches the dent stage, sap beetle will not continue feeding. Thresholds have not been developed for sap beetles in corn. Sap beetles can be a serious pest of sweet corn.
Figure 3. Larvae of a sap beetle species damaging
kernels of an ear of corn. (Photo by E. Nelson, Bugwood.org)
Figure 4. Sap beetle adult. (Photo from