Insect migration is a fascinating natural phenomenon, the study of which can increase our fundamental knowledge of insect population dynamics, behavior, and physiology. Understanding directed insect migration is also important in the fields of pest management and biodiversity conservation. For example, large-scale movements of herbivorous insects can cause substantial economic damage to crop production and forests. Knowing the migratory mechanisms and capacity of these pest species can inform predictive mathematical models that forecast outbreaks and help efforts to limit pest-associated losses. Meanwhile, the identification of factors that influence each of the three stages of migration is essential for conservation efforts of at-risk species, especially when migrations occur across international borders. We need to study the factors that influence migration to make these predictive models more realistic. How do insects migrate? What resources are required to successfully complete migration? By answering these questions, researchers can begin to develop effective conservation strategies to protect migrating populations of threatened insects. Two well-known examples of migratory insects are the migratory locust and the monarch butterfly. Locusts are good examples of pestiferous migratory insects. Some grasshopper species experience developmental changes in overcrowded conditions with low resource availability. Competition for space and resources causes juvenile grasshoppers to develop into migratory forms in the adult stage. These migratory forms are commonly referred to as locusts. Locust exhibit morphological, behavioral, and physiological differences from grasshoppers of the same species in the solitary phase. Migratory forms can have bolder coloration, a greater appetite, shorter lifespans, and lower reproductive rates than solitary forms. Despite lower reproductive rates, the gregarious nature of the migratory form can result in the deposition of thousands of egg pods per square meter of soil during major outbreaks. Locusts also tend to aggregate based on visual and chemical cues, feeding and moving as a coordinated and cohesive unit called a swarm. Locust are voracious herbivores capable of destroying huge areas of vegetation as they migrate, and a swarm can contain millions of insects traveling up to hundreds of kilometers per day. Since ancient times, locust swarms have contributed to human famines across the globe and continue to threaten agricultural production today. There are about a dozen species of short-horned grasshoppers that have a gregarious locust phase. The change between solitary and migratory forms relies on a type of phenotypic plasticity called polyphenism. Phenotypic plasticity is the phenomenon whereby a single organism's behavior, physiology, or morphology changes based on environmental conditions, while polyphenism specifically occurs when an organism has two or more discrete forms, despite having the same genes. A great example of a migratory grasshopper species is the suitably named migratory, locust, Locusta migratoria. When it comes to management of locust populations, action must be taken quickly to prevent devastating effects of outbreak swarms. Locust management is heavily dependent on understanding the factors that promote migratory behavior. Currently, the primary mode of locust management is to control early swarms with insecticides. The financial and ecological costs of managing locusts using insecticides however, are substantial. Insecticide use poses significant potential risks to people and non-target species. With pest management, the best defense is often a good offense, and the best way to manage locust plagues is to prevent them from happening in the first place. Locust swarm formation is often associated with the end of the dry season. Fast vegetation growth that occurs at the end of the dry season promotes a rapid increase in grasshopper population density. These overcrowded conditions induce the migratory syndrome in these grasshoppers, and they develop into the migratory locust phase. Collection and analysis of weather data, ecological conditions, and grasshopper population numbers can help to forecast the timing and location of locust swarms. This kind of early warning and prevention allows for more efficient locust management. Thanks to these efforts, swarming events have decreased substantially in the 21st century. Nevertheless, occasional lapses in monitoring or exceptionally favorable environmental conditions can result in locust swarms like the ones that occurred in 2004 in Africa and 2013 in Madagascar. Migratory locusts are a serious past problem. Fortunately, our understanding of the underlying mechanisms of migratory behavior allows us to restrict the damage these pests can cause. The same concepts can be applied to conservation efforts, which we will discuss in the next video using the famous and fantastic monarch butterfly migration as a case study.
