The yellowmargined leaf beetle (Microtheca ochroloma)—adult females (left) and males (right) shown in dorsal (A) and lateral (B) views above—is a major pest of crucifer vegetables. A new profile in the Journal of Integrated Pest Management offers a guide for growers in managing the pest. (Photo credit: Rammohan R. Balusu, Ph.D.)

In recent years, the demand for organic foods by the consuming public has exploded. Organic food sales surpassed $35 billion in the United States in 2014, up from an estimated $12 billion in 2005, according to the U.S. Department of Agriculture.

While humans are falling in love with organic food more and more, insects are also quite fond of it. Insecticide restrictions on organic crops mean the insects have an easier chance to grab a free meal without getting killed in the process. One insect causing a considerable amount of damage to organic crops in the southeastern United States is the yellowmargined leaf beetle (Microtheca ochroloma).

The beetle is usually susceptible to synthetic insecticides, but, in the absence of those insecticides in organic systems, the beetle has become one of the major pests of organic cruciferous vegetable crops, such as cabbage, cauliflower, collard, and radish. A new profile of M. ochroloma in the open-access Journal of Integrated Pest Management (JIPM) offers growers a useful guide for understanding how to manage the pest.

Past research has shown that the yellowmargined leaf beetle prefers some crucifers over others; a behavior that can be used to manage the beetle via a method known as trap cropping. Trap cropping involves planting a border of crops that the beetle is most attracted to—turnips and Napa cabbage—around a main crop like cabbage or mustard. By doing this, growers can reduce the beetle’s impact on the main crop. They can then apply organically approved insecticides on the trap crop to reduce or eliminate the use of insecticides on the main crop, says Rammohan R. Balusu, Ph.D., a research fellow in the Department of Entomology and Plant Pathology at Auburn University and lead author of the JIPM article.

“Although the use of trap crops for M. ochroloma management is gaining popularity through extension publications and hands-on training, it is still currently an underutilized tactic,” Balusu says. “Our research showed that farmers that adopt the integrated trap crop-biopesticide strategy will likely make on average $232 per acre more than those using the growers’ standard practice.”

Yellowmargined leaf beetle adults and larvae feed voraciously on crucifers, causing severe defoliation such as in the cabbage shown above. (Photo credit: Rammohan R. Balusu, Ph.D.)

In their article, Balusu and his colleagues summarize the basic life stages, ecology, and feeding behavior of the yellowmargined leaf beetle, and they identify various other management methods available to organic crucifier growers, including:

• Cultural control, such as cultivation and clean-up of fields immediately after harvest, to reduce plant debris that serves as shelter and food for overwintering beetle populations.
• Biological control, such as introduction of the spined soldier bug (Podisus maculiventris), a predator of the yellowmargined leaf beetle.
• Chemical control, such as application of Entrust (spinosad) and PyGanic (pyrethrin), which are approved by the Organic Material Review Institute (OMRI) for use in organic crop production.

“During warm conditions—around 25 degrees Celsius—the beetle can complete its entire lifecycle in less than a month, allowing population to build up very quickly and destroy an entire crop in no time,” says Balusu. “Scouting the crop frequently and regularly could help diagnose the pest early to make timely management decisions.”

Currently, no scientifically confirmed economic thresholds exist for managing yellowmargined leaf beetle, though Balusu and colleagues suggest a level of one adult per plant. Balusu says research is currently ongoing to establish a field-based threshold. Regardless, a well-rounded combination of methods is recommended.

“An integrated pest management strategy, which combines cultural control tactics such as trap cropping, pest monitoring, and targeted application of OMRI-approved insecticides, is the most effective and ecologically sustainable method of managing M. ochroloma populations in crucifer production systems,” they conclude.