Ecology and population dynamics of solitary Red Locusts in southern Madagascar

Abstract

This paper summarizes eight years of field study on the Red Locust, Nomadacris septemfasciata (Serville) in southwestern Madagascar and presents management recommendations for its control. This crop pest exhibits a fairly uniform annual life-cycle phenology in southern Madagascar, which involves seasonal migration and adult reproductive diapause. There is one generation/y. Eggs are laid at the beginning of the rainy season in November and December. Eggs hatch in 24-36 d, and the hatchlings reach adulthood in 50-70 d. Fledgling adults enter a reproductive diapause in March and April, and then migrate north and northeast to higher elevations (refuge area where rainfall is > 80 cm/y) where they remain throughout the dry season (May-October). In November (the beginning of the rainy season), the adults migrate south and west to lower elevations (breeding area where rainfall averages 40-80 cm/y) where they mate and initiate oocyte development. Females possess ∼ 162 ovarioles, and typically lay two or three egg pods, each containing ∼ 100 eggs. The six-month adult reproductive diapause is controlled by photoperiod. Eggs and nymphs can experience high mortality, and hence, these stages are key to predicting population dynamics. Based on our findings, we recommend concentrating surveys in the main breeding areas (including one small southwestern fringe with the strongest probability of gregarisation and outbreak), better monitoring of local rainfall abundance and distribution, and better monitoring of deforestation, which increases locust habitat.