Onion thrips (Thysanoptera: Thripidae) damage and contamination in sauerkraut.

J. Econ. Entomo!. 75: 492-494·(1982) Studies conducted to determine Thrips tabaci Lindeman damage and contamination in sauerkraut revealed that both occur at detectable levelsin processedcabbage, althoughsuch levelsare much lower than predicted from examination of fresh cabbage. Addition of the chemical preservativessodium benzoate (0.1%) and potassiummetabisulfite (0.05%) had no effect on plant tissue damage or insect contamination. Although tolerance levels for insect contamination in many other vegetableshave been established, the FDA has not established such a tolerance for insect contaminants in sauerkraut. To avoid discretionaryseizure, and in light to these findings on this newlyimportant pest of cabbage, guidelinesshouldbe establishedfor plant injury and insect tolerances. Materials and Methods Detection of Thrips Contamination and Plant Injury About 125 heads of cabbage, cv. 'Hinova,' were harvested from a commercial field known to have a high level of thrips-infested cabbage and processed at the New York State Agricultural Experiment Station's Food Processing Laboratory. Cabbage was divided into three treatments: (1) no damagetrimmed of green and thrips-infested leaves; (2) commercial grade-trimmed of green leaves only; and (3) extreme damage--containing only thripsinfested leaves. Treatments 1 and 2 were replicated three times with 10 kg of shredded cabbage each, whereas treatment 3, because of a limited quantity of severely infested leaves, was replicated twice with one lO-kg and one 8-kg sample. Cabbage leaves were segregated into one of the three treatments and shredded. During shredding, small subsamples (700 g) of shredded cabbage were collected to determine levels of insect contamination and thrips damage before processing. Five hundred shreds from each subsample were checked for thrips injury, and the remainder (ca. 600 g) was washed with 1 liter of water, filtered, and examined for insect fragments (all examinations for insect contaminants followed accepted practices [Horwitz 1980)). The eight main samples, containing 8 to 10 kg of shredded cabbage, were salted with sodium chloride (2.25% wt/wt), and were packed in plastic containers (35 by 25 cm). Containers were capped with a water seal (lO-cm depth) to insure anaerobiosis and incubated at 20°C. After 8 weeks of incubation, each container was drained of brine. A 200-ml sample of the brine was filtered and examined for thrips contamination. The drained solids from each container were divided into four sections, i.e., top, surface spoilage (an effect normally observed in sauerkraut fermentation), and equal thirds of the remainder. This partitioning was done to determine the distribution of thrips within the sealed tank. Three 500-g samples of each of the four sections per container were washed with 1 liter of water and examined for thrips contamination. The remaining solids (except the spoiled section)