Blister beetles (soybean)
Authors: Buyung Hadi and Jeffrey Bradshaw
All blister beetles that are known to infest soybean plants are of genus Epicauta: the margined blister beetle, Epicauta funebris, and striped blister beetle, Epicauta vittata. These species of blister beetle are native to North America and are commonly occur in the eastern half of the US.
Adult blister beetles' heads are broader than their neck (prothorax) regions and they have moderately long antennae and legs. The margined blister beetle is black, gray or a mixture of both while the striped blister beetle is orange with dark stripes.
Newly hatched larva are whitish in color, but soon turn reddish brown. First instar larva forages actively. Later instar larva is sedentary and grublike.
Life Cycle and Seasonal History
In most areas in the Northern Plains, blister beetles only reproduce once per year but in the southern states they can produce two generations per year. Adults usually occur between summer and early fall. The precise timing and period of adult occurrence vary between locations. Blister beetle adults are active both day and night, although at warmer periods of the day they tend to seek shelter in shaded plant parts.
Upon mating, female blister beetle lay eggs in the soil. Hatching occur in 10 to 16 days. The first instar larvae readily disperse and forage for grasshopper eggs. The immature form of blister beetles are predaceous. Because grasshopper eggs are an important larval food source, blister beetle abundance is influenced by grasshopper abundance. The number of blister beetles may significantly increase in years with high grasshopper population and the years immediately after. Nevertheless, if grasshopper outbreaks are short lived and infrequent, the resulting blister beetle abundance may not be significant. Blister beetle larvae molt 4-8 times before pupation. The pupal stage is found in the soil and it greatly resembles the adult form albeit with legs and wings tightly drawn to the main body. The pupae are initially whitish in color and grow darker as they mature.
Adult beetles feed on various host plants including soybean and alfalfa. In areas where the beetles only produce one generation per year, the next generation of beetles overwinter in the soil in larval form.
Plant Injury and Damage
Adult Blister beetles mainly primarily feed on leaves and generally has minimal economic importance. The adults also may feed on soybean flowers, young pods or tender stems although these parts are not commonly injured.
Adult blister beetles have a defensive strategy called reflex bleeding. When harassed, the beetles secrete droplets of blood (insect blood is called hemolymph) through their joints. The blood contain a toxic substance called 'cantharidin'. Therefore, the beelte uses its blood as a deterrent. Direct contact with this substance may produce blisters on human skin, thus the name 'blister beetle'. Horse ingestion of certain species of blister beetle (e.g., Epicauta vittata) in hay may be lethal.
Blister beetles have been shown to transmit Bean pod mosaic virus.
Adult blister beetles tend to aggregate for mating and feeding. Visual inspections of plants may reveal aggregations of blister beetles on a few isolated plants. Spot foliar pesticide application on infested plants may be sufficient to control for blister beetles. The period when alfalfa is cut for hay or weedy areas around a particular soybean field are mowed may be a good time to scout for blister beetles.
Other Online Resources
For information regarding labels of chemical control options, please visit Agrian.com