Locusts in the World

Abstract

Locusts (Orthoptera: Acrididae) form dense bands and swarms that can cause substantial damage to pastures and crops. And a feature that makes locusts particularly devastating is the ability of migrating swarms to appear without warning in large numbers in previously uninfested areas, overwhelming local crop protection programs. To reduce damage, many governments conduct locust control programs: they aim to begin treating the locusts before they reach crops to try to reduce the size of swarm invasions of cropping areas. Locusts alternate between periods of low numbers (recessions) and very high numbers (plagues). When in low numbers, locusts are quite dispersed, but favorable conditions allow populations to increase and the dispersed locusts undergo a behavioral change where they come together to form bands and swarms. Most locust management programs rely on regular monitoring of locust populations and when bands or swarms are detected, treatment programs begin. But these early intervention programs have the greatest chance of success if they are combined with a reasonably good understanding of the critical factors that lead to population upsurge and of where locusts are more likely to be. When such factors occur, then extra resources need to be made available for survey and treatment. It takes several generations of successful breeding for initial localised outbreaks to reach plague proportions: and the aim is to rapidly find and treat as many of the locusts as possible in each of the generations of increase as part of a strategy of preventive control (la lutte preventive or la lucha preventiva). Such treatments can limit the rate of increase in each generation, reducing the consequent damage when the locusts reach crops. Treatments have relied on the use of various chemical pesticides, and the use of chemical pesticides will continue. But increasing constraints on the use of chemical pesticides mean that alternatives need to be investigated as part of treatment programs to ensure locusts are treated whenever and wherever they are found.