Flea Beetles

 Year 1 (2006) Summary

The three flea beetle species in the Willamette Valley that are capable of inflicting economic damage on tubers are the tuber flea beetle (Epitrix tuberis), the tobacco flea beetle (E. hirtipennis), and the western potato flea beetle (E. subcritina). The first two of these species were found in the potato fields on all five of the sampled farms, and the third species was present in very low numbers at a few of the farms. Tuber flea beetle numbers were about twice as high as those of tobacco flea beetles.

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Flea beetle populations increased at the edges of the potato fields more rapidly than at the inner areas of the fields. This indicates that flea beetles initially came from overwintering sites outside of the potato fields, and gradually spread into the inside of the fields from the edges. The ‘edge’ area of the field was defined as potato plants within 5 meters of the outside edge of the field.

The extent of tuber damage in each of the five fields relative to flea beetle populations and the timing of their arrival was also assessed. Three of the fields showed the expected higher or lower amount of damage with higher or lower flea beetle populations respectively, but two of the fields showed the opposite trend, with high populations yet comparatively little tuber damage. There are many possible management and/or biological factors in these fields that could cause the large flea beetle populations to not reach their typical damage potential, and this also shows that the beetle population levels are not always reliable predictors of damage in a field.

Since tubers are more susceptible to damage from increasing numbers of flea beetle larvae as the season progresses, the time of arrival of the beetle adults to a field in the spring could also be an indicator of the extent of damage in a given field. The timing of arrival of flea beetle adults also turned out to not be a reliable predictor of tuber damage, but the sampling at the beginning of spring may not have been intensive enough to catch the first individuals. The plan for year 2 is to increase the intensity of flea beetle sampling in the early spring to confirm the actual timing of arrival, as well as to provide biofix information for predictive tuber and tobacco flea beetle degree day phenology models that are being developed.

yellow_sticky_trap.jpg Sampling and diagnostic methods for flea beetles were tested and developed, and these have been summarized in an identification and monitoring worksheet for use in the field. Sweep netting of potato plants was more efficient than simple visual observation for assessing beetle numbers in the crop field. Yellow sticky traps yielded some information on flea beetle numbers, but they were not as efficient as sweep netting, and are probably more useful for assessing the timing arrival of the first flea beetles rather than population levels. Since flea beetle populations were shown to increase at field edges first, monitoring efficiency can be increased by focusing on these parts of the field. A flea beetle damage rating system was also developed to quantify damage for the consistent diagnosis of flea beetle damage.

Future work
The flea beetle management strategies the farmers are most interested in investigating in the 2007 season are entomopathogenic nematodes, covering the base of the potato plants with soil or a mulch to prevent oviposition, and early planting and harvest to get the tubers out before they accumulate significant damage. We will also try to examine the overwintering sites on each farm as sources, and combine this information with the information produced from the other experiments into a set of IPM recommendations that will be presented in discussions and summarized in either handbook or information sheet form.