Citrus Thrips (Thysanoptera: Thripidae) Phenology and Sampling in the San Joaquin Valley

Citrus thrips, Scirtothrips citri (Moulton), was monitored over a 3-year period in San Joaquin Valley, Calif., navel orange groves to compare population trends observed using alternative sampling methodologies and to determine thermal accumulations required for development. Citrus foliage monitoring did not indicate a direct relationship between timing of the end of shoot growth, petal fall, and the level of citrus thrips fruit scarring. Over the first three spring generations, citrus thrips were found in greatest numbers in the northeast quadrant, although first-generation larvae in the south developed more rapidly than larvae in the north. Comparisons among sampling techniques (D-Vac, pupation papers, ground traps, yellow cards, and fruit counts) and their ability to predict scarring were inconclusive. The period between the first and second citrus thrips generations measured from the peak of a particular life stage to the next peak was 156 degree-days above a lower threshold of 14.59°C. The period between the second and third generations was not consistently related to heat units based on this lower threshold.