Influence of relative humidity on the expression of twolined spittlebug (Hemiptera: Cercopidae) feeding injury in turfgrass genotypes

The twolined spittlebug, Prosapia bicincta (Say) (Hemiptera: Cercopidae), is an important insect pest of turfgrass in the eastern United States. Although twolined spittlebug infests most warm-season turfgrasses, the influence of low and high relative humidity (RH) on the expression of feeding damage in warm-season turfgrasses is not well understood. Experiments were conducted in which five warm-season turfgrasses were caged with ten twolined spittlebug adults and exposed to 40% and 95% RH for 5 days. The extent of damage was measured with a SPAD meter (chlorophyll content), and ratings of greenness, yellowness, and purpleness were obtained using a scale system. Physiological parameters such as stomatal conductance (GS), photosynthesis (A), evapotranspiration (E), and water use efficiency (WUE) were measured. Under both 40 and 95% RH, bermudagrass [Cynodon L.C. Rich, spp.] exhibited injury symptoms after twolined spittlebug exposure. The rate of A was lower in the presence of twolined spittlebug in bermudagrass under both RHs. Injury symptoms in centipedegrass [Eremochloa ophiuroides (Munro) Hack] were only observed under high-RH conditions, whereas in zoysiagrass [Zoysia matrella (L.) Merrill.] symptoms were only observed under low RH. Minimal levels of symptom expression were observed in St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and no feeding symptoms were observed in seashore paspalum [Paspalum vaginatum Sw.] under low RH. Overall, the presence of twolined spittlebug A was influenced by high RH, whereas WUE was affected by low RH in most of the turfgrass genotypes.