Influence of plant age, temperature, and moisture on Protaphorura fimata feeding injury on lettuce in the Salinas Valley of California, USA

Abstract

AbstractProtaphorura fimata Gisin (Collembola: Onychiuridae) is a serious pest of lettuce, Lactuca sativa L. (Asteraceae), seedlings in the Salinas Valley of California, USA. Little is known about the growth stages at which lettuce seedlings are vulnerable to P. fimata feeding, and how temperature and soil moisture affect symptoms and severity of feeding injury. To determine the most vulnerable lettuce seedling stage to P. fimata feeding, sets of lettuce seeds were planted for six consecutive days on the soil within clear plastic cups. On the seventh day, all plants were exposed to 100 P. fimata for a week. The results indicate that the number of germinated seeds, fresh weight, and dry weight were significantly lower in 1‐day‐old seedlings than in 3‐ to 6‐day‐old seedlings. To determine effects of soil moisture on P. fimata feeding, various amounts of distilled water (1.5, 2.5, 3.5, 4.5, 5.5, or 6.5 ml) were added to 10 g of soil in containers planted with lettuce. Plants were later exposed to 100 P. fimata for a week. Results indicate that the seedlings that received 6.5 ml water had significantly lower seed germination and fresh weight, but a greater percentage of injured seedlings and more feeding punctures per germinated seed, than the seedlings that received 2.5, 3.5, 4.5, or 5.5 ml of distilled water. In the temperature assay, 100 P. fimata were exposed to lettuce seeds maintained at 5.4, 10.8, 15.5, 21.2, 29.1, or 33.0 °C for 31, 12, 8, 7, 5, and 5 days, respectively, until the first pair of leaves became fully expanded. Protaphorura fimata caused feeding injury on the germinating lettuce seeds in all temperature ranges except at 33.0 °C. The number of seeds germinated and fresh weight of seedlings were significantly lower in the seedlings exposed to P. fimata than unexposed seedlings at all the temperature ranges.