Movement patterns and phenology of the tobacco thrips, Frankliniella fusca (Hinds), in Virginia peanuts
Birdwhistell, Amie J.
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The immigration, population dynamics and intra-field movement patterns of the tobacco thrips, Frankliniel/a fusca (Hinds), in peanuts were studied in 1990 and 1991 in the City of Suffolk, Virginia. The long-term goal was to improve our understanding of the role of tobacco thrips in the epidemiology of tomato spotted wilt virus in peanuts; the short-term goal was to develop quantitative descriptions of thrips development and movement for inclusion in a systems model intra-field movement patterns were assessed by establishing an isolated population of thrips in the center of a (67 m2) peanut field and monitoring the subsequent spread of thrips throughout the field. Thrips did not redistribute step-wise, as expected. Instead, thrips dispersed evenly throughout the field. However, failure to observe step-wise movement was probably due at least in part to the failure of insecticides to control the thrips in the corner areas of the experimental fields. Immigration and inter-field movement of adults were monitored with sticky traps. Thrips were caught on these traps only during the immigration period, which ended approximately two weeks after plant emergence. The spatial pattern of thrips immigration indicated that their movement was strongly influenced by wind direction and also by field borders. Proximity to fields planted the previous year in peanut also apparently influenced immigration. A computer model was developed based on previous and recent laboratory studies to simulate the phenology of the tobacco thrips as a function of temperature. The model was validated using field data from the 1991 season and used to help explain apparent anomalies in the 1990 data. The model confirmed that thrips damage to peanut was caused by two generations (F1 and F2) during June and July. Model results also suggested that rainfall was a significant mortality factor in thrips population dynamics. A second model was developed to simulate thrips movement in relation to wind speed and direction. This model will be used in future studies to test hypotheses about the ability of thrips to move within and between fields.
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