Observations on the biological and ecological behaviour of Rhammatocerus schistocercoides (Orthoptera:Acrididae)/in Colombian high plateaux

Abstract

The llanera locust Rhammatocerus schisto­cercoides (Rehn) (Acrididae: Gomphorce­rinae) because its high population density and gregarious behaviour affect extensive areas of native savanna, improved pasture-land, and crops of economic importance such as rice, maize, sugar cane and sorghum, and can cause damage to cattle and crop production in the region. In order to generate basic information concerning the biology and some preliminary data on the behavior and ecology of this insect, a study was conducted in CORPOICA at the Carimagua Research Center (Puerto Gaitán, Meta) with the following objectives: To study chronologically the sexual development, copulation, and oviposition, to determine the polychromatism of individuals and to determine the habitat and food preferences of the insect on its native savannas. Observations were made between August 1996 and September 1997 at three different points: A first point where the landscape is ubicated on the plains, a second point consisting of rolling flatland, and a third site composed of hills. The results obtained show that the invasion of the insect comes on a Nort-East from South-West line. The avera­ge duration of the adult was 180 days, distributed between young (sexually immature), and adults during the first 120 days from the emergence as imago to sedentary (sexually mature) adul.ts which began their first copulation and the first oviposition in February and March. The first patch-stain of nymphs in the first instar stage occurred 25-30 days after oviposition. In the patch-stain, individual insects presented 4 different phenotypic presentations, classic fi ed A, B, C, and D, according to corporeal coloration. The swarm of adul.ts wandered from the plateaux constituted by clay soils and lignified native vegetation to the dissected plateaux, their insect wandered from of the alluvial plains on the native flatlands where vegetation was regenerating after burning off to sandy soils. In this place they became sedentary, cannibalised elytra and wings copulated and laid eggs. The. The number of eggs per oviposition was a maximum of 51 and a minimum of 25 per ootheca. The time between oviposition and emergence was 25-30 days rider semi-field conditions, hatching i.mmediately after the first rains. In the stage of sexual maturity, they were strongly attacked on the native savanna, two and three weeks after turning off, consuming in order of preference. Axonopu,s' spp., Mesosetum spp., Paspaltunpectinanun, Trachypogon vestitus, Andropogon spp. and Trasya petrosa, with an average of 20kg/clay of consumption per hectare. for a density of 4 adults per square meter.