Cannibalism, oviposition and egg development in the edible long-horned grasshopper, Ruspolia differens (Orthoptera: Tettigoniidae) under laboratory conditions

Abstract

Reliance on seasonal wild harvests of the edible long-horned grasshopper Ruspolia differens (Serville) (Orthoptera: Tettigoniidae) needs to be broken through developing efficient mass rearing protocols. This study aimed at boosting productivity of laboratory colonies of R. differens through understanding ways of minimising cannibalism, selecting suitable oviposition substrates and enhancing egg development and hatchability. Firstly, we investigated the extent of cannibalism in a colony of R. differens relative to total mortality, sex, diurnality, growth stage, body parts eaten and visual barriers (presence/absence of cardboard egg trays). R. differens cadavers recovered from cages with/without the egg trays were scored for cause of death (cannibalism/other), time of death (night/day), sex, growth stage and body part devoured. Secondly, cotton wool and leaf sheaths of Pennisetum sp., maize and Panicum sp. were evaluated for oviposition preference by R. differens. Eggs oviposited in each substrate were incubated to determine developmental duration and hatchability. Thirdly, we tested effect of moistening R. differens eggs on incubation period and hatchability in intact and opened leaf sheaths against unmoistened eggs in intact sheaths as a control. We found that cannibalism accounted for 49% of R. differens deaths with 83% of victims being adults. Males and females were equally susceptible to cannibalism. Over 97% of cannibalism occurred at night and presence of egg trays almost doubled incidence of cannibalism. The thorax was the most preferred body part, which was consumed in 77% of cannibalised individuals. Maize and Panicum sp. were preferred for oviposition over Pennisetum sp. and cotton wool. Opening of egg-laden leaf sheaths reduced incubation period by 0.4 days. Unmoistened eggs didn’t hatch after incubation for 25 days, but 65% of them hatched within 11 days upon moistening. These findings offer guidelines for improvement of protocols for mass rearing of R. differens for human consumption and other uses.