Low-Temperature Survival Strategies of Potato Leafhopper (Homoptera: Cicadellidae)

Abstract

Studies were conducted to provide information on the behavior of nymphs and adults of potato leafhopper, Empoasca fabae (Harris), under sudden low-temperature conditions, the host-finding ability of potato leafhopper nymphs, and on the soil cooling rate during freezing and subfreezing temperatures. Avoidance of sudden low temperatures by susceptible life stages decreases low-temperature mortality. The percentage of potato leafhopper nymphs and adults dropping off leaf surfaces when exposed to experimental temperatures of 0, 5, and 10∘C for 1 h were measured. More fourth and fifth instars dropped off the leaves at all three temperatures than did first to third instars and adults. Significantly more insects of all ages dropped off the leaves at 0∘C than at 5 or l0∘C. The percentage of potato leafhopper nymphs relocating host plants at two plant densities were measured. Significantly more insects were found within 15 cm of the release point(s) (37.8%) than were found 15–30 cm (27.0%), 30–45 cm (17.4%), or 45–60 cm (19.3%) from the release point(s). No significant differences were found in host-finding ability between instars. The percentage of nymphs able to relocate host plants ranged from 24 to 27%. Success in host relocation by nymphs was not influenced by host plant density. The cooling rates of soil samples acclimated to 4.4∘C were measured 3.0 cm below the soil surface, on the soil surface, and in the leaf canopy for three experimental temperatures (0, −5, −l00∘C). Leaf canopy temperatures reached 0∘C in 15, 15, and 5 min for the three temperatures, respectively. Soil surface temperatures reached 0∘C in 115, 35, and 15 min, respectively. Soil temperatures at the depth of 3.0 cm did not drop to 0∘C within 3 h under any of the three temperature regimes used in these experiments. Survivorship of potato leafhopper nymphs when exposed to long durations of freezing or subfreezing temperatures may be overestimated when using available low-temperature mortality information without taking into account the insect behaviors and host finding abilities at the low temperatures reported here.