Models for estimation of population density of late instar nymphs and fledglings of the desert locust,Schistocerca gregaria(Forsk.)

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Abstract
Precise estimation of numbers of gregariously behaving desert locust, Schistocerca gregaria (Forsk.), populations is essential for the development of an economical control strategy. Such an estimate should facilitate proper deployment of scarce available resources frequently needed at widely scattered sites in infested areas. A simple, less time‐consuming, yet precise and cost‐saving technique for estimating absolute numbers of locusts based on plant counts has been developed. It was observed that on the Red Sea Coast of Sudan, which is a major locust breeding and recession area, locusts take shelter in different bushy plants including Panicum turgidum and Salsola forskalii. The numbers of locusts present in each plant were found to be highly correlated with its size. Simple linear regression models accounted for about 70% variability, when plant perimeter was used as a predictor variable. These models can be used to estimate locust numbers on a plant of a given size. Thus the number of infested plants in a sample area can be counted, and the locust density calculated mathematically. It was observed that in the study area P. turgidum and S. forskalii covered about 3·18% and 4·05% of the ground surface, respectively. The estimated density of locusts was 15·7 × 106 individuals per km2 in a total infested area of 4 km2. Hence the swarm which was expected to fly out of that area would contain approximately 62·8 × 106 locusts.