Elson Shields
Department of Entomology
Cornell University
Ithaca, NY

Migration of Potato Leafhopper (E. J. Shields & A. M. Testa)

Empoasca fabae, the potato leafhopper (PLH)

In 1998, sampling flights were taken on 8 different dates between 8/28 and 9/11. A total of 8 sampling dates is a very small data set to draw any definitive conclusions on the general environmental cues used by PLH to initiate their fall migration. The evening activity period between 1 h before to 30 min. after sunset was consistent regardless of barometric pressure characteristics. PLH adults would appear around the RPV landing/service area at the same time each night regardless of weather conditions and independent of the aerial capture data, suggesting that falling barometric pressure can be correlated with increased flight activity of diapausing female PLH at ca. 30 m above an alfalfa field. In addition, these data suggest that leafhoppers conditioned to initiate long-range fall migration respond to a drop of barometric pressure lasting >12 h prior to the evening activity period by launching upward into the planetary boundary layer where long-ranged transport occurs.

Taylor & Reling (1986) proposed that PLH initiate their return fall migration prior to the arrival of the low pressure front in either calm winds or in winds with a southerly flow. As the leafhoppers are pulled into the front at an upper altitude, they fold their wings in response to air temperatures dropping to <12 °C and then drop out of the front into the warmer air temperatures at lower altitudes behind the front and resume flying. The winds behind the front have a northerly air flow and would transport the leafhoppers southward as long as the leafhoppers remain airborne. Only one of the aerial sampling time periods (31 Aug.) had weather conditions similar to the above described pattern and we collected only 2 leafhoppers aloft. In contrast, three of the aerial sampling periods occurred just after the passage of a low pressure front and a large number of leafhoppers were collected aloft (29 Aug. - 9 PLH, 2 Sept. - 8 PLH, 6 Sept. - 18 PLH). Two of the sampling periods (1 Sept., 5 Sept.) occurred just after the passage of the highest pressure during the past 24 h and ca. 24 h before the passage of the low pressure front. Under these conditions, large numbers of leafhoppers were flying aloft as reflected in the aerial collection data (1 Sept. - 15 PLH, 5 Sept. - 12 PLH). We believe that PLH in reproductive diapause within a physiological window shortly after eclosion become conditioned to initiate their fall return migratory flight during their normal dusk activity period after barometric pressure has been declining for more than 12 h or when declining barometric pressure immediately follows a high pressure ridge passing through the area. Initiating long-ranged movement under either of these conditions would facilitate the efforts of PLH to migrate south to the overwintering area. However, a much larger sampling data base is required to adequately substantiate our conclusions.

While the current fleet of 2.4 m RPVs is providing exciting data, the aerial density of potato leafhopper over populated alfalfa fields ranges between 0-4 individuals per 1000 m3 with one individual per 1000 m3 of air typical. The current RPV design requires 30 min. sampling time to sieve 5000 m3 and collect between 0-20 leafhoppers with less than 10 collected leafhoppers typical (50% are females). These low numbers of collected leafhoppers exclude any biological study with the captured leafhoppers and only allow conclusions about reproductive status based on dissection. Laboratory verification of reproductive status requires a larger number of females to be collected during each flight and conclusions on flight behavior into the planetary boundary layer could be strengthened with larger collections of individuals in smaller time slices.  To solve this problem, we have developed two larger RPVs capable of sampling larger quantities of air per time slice. The 3 m wingspan RPV (5 hp) is estimated to increase the sampling capacity by 50-60% (7500-8000 m3/30 min.) over the currently used design of 2.4 m, while the 4 m wingspan RPV (14 hp) is estimated to increase the sampling capacity by 140-200% (12,000-15,000 m3/30 min.). However the cost of each RPV rises from about $2500 for the 2.4 m RPV to $6000 for the 3 m RPV and $12,000 for the 4 m RPV. During the past month, the first prototype of each of the 2 larger RPVs have been flown. The winter will be utilized to develop and mount the net system and both airplanes will be ready for aerial sampling in the 2000 growing season.

not all flights are successful...

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