Physiological and behavioral adaptations of three species of leafhoppers in response to the dilute nutrient content of xylem fluid

Abstract

Physiological and behavioral processes of three species of leafhoppers were examined in relation to the extremely dilute content of their food source (xylem fluid). Segregated sexes of Homalodisca coagulata (Say), Homalodisca insolita (Wlk.) and Cuerna costalis (F.) were caged on two hosts, Lagerstroemia indica L. and Catharanthus roseus (L.). Excreta was analyzed and compared to the composition of xylem fluid of the hosts during day and night feeding. Both xylem fluid and insect excreta were analyzed for amino acids, organic acids and sugars and excreta was also analyzed for common excretory products. Efficiencies of metabolic conversion of organic compounds (defined by quantity ingested versus quantity excreted), and total nitrogen and carbon retention were calculated. Diurnal feeding patterns as well as total daily ingestion rates were recorded. Four primary similarities were noted in diet utilization regardless of leafhopper species, host species or sex: (1) excretion of ammonia as the primary waste product; (2) high efficiency of conversion for all organic compounds ingested from xylem fluid; (3) high daily feeding rates (100–300 times dry body weight per day and (4) adjustment of feeding rates to diurnal fluctuations in xylem fluid chemistry. Although these processes were operative for all leafhoppers examined, the extent of their usage and subsequent energy gain and nitrogen accumulation varied greatly with host species and insect sex. These processes maximize efficiency of diet utilization and are discussed in relation to nutritional and caloric requirements of xylem feeding insects.