Population Dynamics of Brachycorynella asparagi (Homoptera: Aphididae) on Undisturbed Asparagus in Washington State

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Abstract
Dynamics of the asparagus aphid, Brachycorynella asparagi (Mordvilko), were studied in two mature asparagus fields and one immature field for a minimum of two seasons. To minimize disturbance to the asparagus, no harvesting, spraying, or cultivation was done. Numbers of B. asparagi were low early in the spring and increased to a peak in late June or July or in September to early October. No midseason peak was observed. Fields with an early summer peak had a midsummer low point and usually a late summer peak. Decline of aphid numbers in the fall coincided with egg laying that started during the last week of September when day length was about 12 h. Production of winged aphids and parasitism by Diaeretiella rapae (McIntosh) were density-dependent on some plots. These mortality factors undercompensated for changes in aphid density and failed to keep aphid numbers at acceptable levels. No consistent, significant correlations between temperature or rainfall and aphid numbers were found. Egg hatch occurred shortly after the first asparagus spears emerged in the spring. Predicted time of egg hatch based on degree days was within 1 d of observed hatch. Growth of asparagus plants during a growing season had a weak, inverse relationship to aphid numbers.