Trap crop special
Finnish researcher finds success alluring pollen beetle's away from the cauliflower

Posted February 16, 2005: Trap crops are used to lure pests away from a commercial crop by presenting the pest with a more attractive alternative. Trap crops are planted near the commercial crop with the hope the damaging insect will feed on the trap crop leaving the commercial crop alone. Although the concept makes rational sense, it is not as simple as it sounds, according to research being done in Finland there are several criteria that must be considered before deciding on a trap crop.

First, researcher Heikki Hokkanen -- University of Helsinki, Laboratory of Applied Zoology who has found encouraging trap cropping results for carrot psyllid (Trioza apicalis) and the cabbage maggot (Belia radicum) -- looked at characteristics of pests including flying ability, colonization mode, mobility pattern and movement orientation but concluded that few patterns emerged in regards to pest susceptibility to a trap. He did find that insects specializing in one or a few hosts were more likely to be oriented to the trap crop than were generalized pests. He also found trap cropping to be more effective if only one generation spends a short time, rather than multiple generations over a sustained period, attacking the main crop.

In 2003 Hokkanen established a residence index (RI) for how long an insect remained on the plant. The RI can be used to predict the effectiveness of a plant as a trap crop. Using the index a graph can be drawn to calculate the percentage of trap crop needed to keep a determined percentage of the pests off the main crop. Hokkanen then used the RI to set up what he called the “perfect” trap cropping experiment.

Every August, cauliflower, canola and other crucifers in Finland and England are hit hard by the pollen beetle (Meligethes aeneus). Hokkanen hypothesized this was because there were few good smelling crucifers with pollen available during late summer. He further reasoned that if the beetles were presented with a more appealing offer they would leave the cauliflower, canola and other crucifers alone.

To test his hypothesis Hokkanen planted a row of Brussels sprout trap crops next to a field of cauliflower. He found that the trap crop reduced losses from 35% to 3% during the first year.

While Hokkanen remains an advocate of trap cropping he also warns it is not economical or effective in all situations. He suggests trap crops are best used when a non-random pest is terrorizing a high-value crop on a rather large acreage.

Heikki Hokkanen's research was presented at the 2003 Entomological Society of America's (ESA) annual meeting in Cincinnati, Ohio and reported in the September/October 2004 edition of the IPM Practitioner.

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