Defensive Secretion Production in Lubber Grasshoppers (Orthoptera: Romaleidae): Influence of Age, Sex, Diet, and Discharge Frequency

Abstract

The lubber grasshoppers Romalea guttata (Houttuyn) and Taeniopoda eques (Burmeister) discharge a defensive secretion from paired metathoracic spiracles. The amount of stored secretion varies greatly among individuals and is influenced by age, stage, sex, diet, species, body weight, and prior discharge. Later instars possess more secretion than younger instars and females possess more than males. When lubbers molt, all stored secretion is lost; thus freshly molted insects lack exudate. Newly molted adult lubbers increased the amount of stored secretion at an age-related variable rate that peaked on day 4 in T. eques and day 7 in R. guttata. Thereafter, secretion production continued, but at reduced rates. In adults of both species, secretion volume was positively correlated with body weight. In T. eques, discharge of secretion from the spiracles does not influence the rate of filling of the gland reservoir. In R. guttata, a polyphagous diet or a monophagous diet of onion leaves, Allium sp., produced significantly more secretion than diets of wild cucumber, Melothria pendula L., or grapefruit, Citrus paradisi Macfady. leaves. Wild R. guttata adults have more secretion than wild T. eques adults, possibly because of the latter's adaptation to a dry desert environment. This study suggests that numerous factors influence secretion volume and hence defensive efHcacy in lubber grasshoppers. Lubber predators are thus confronted with a variably defended prey, whose defensive capabilities increase over time and with certain diets.