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The current paper provides a detailed review of the historical outbreaks of each of the four plague locust species found in South Africa, namely the brown locust, the African migratory locust, the red locust, and the southern African desert locust. The history and dynamics of the plague infestations and the major local outbreaks are summarized. The typical patterns of the outbreaks of the different species are described, and the threat of these locusts to agriculture in South Africa is defined. The brown locust produces regular outbreaks in the semi-arid Karoo, with large-scale eruptions of plague proportions occurring about once per decade. Patterns of outbreaks often repeat themselves, but the sheer size of the plague outbreaks is almost impossible to stop, and the brown locust has the potential to threaten food security throughout southern Africa. The African migratory locust produces outbreaks in some of the main maize and wheat cropping areas where it is difficult to control. This locust has taken advantage of the man-made crop environment to produce an extra generation per year that was not previously possible in the original grasslands. The coastal area of KwaZulu Natal Province in South Africa was a prime reception and breeding area for plague invasions of the red locust in the past, and the country, therefore, relies on the successful control of outbreaks in east and central Africa to prevent the recurrence of the plague invasions. The southern African desert locust occurs in the Kalahari Desert area, and outbreaks requiring chemical control are rare.

We provide an exemplar study for investigating the manner and extent to which plant secondary metabolites (PSMs) influence nutritional regulation in herbivores selecting among multiple foods. Two experiments were performed using the African migratory locust, Locusta migratoria (L.). In both cases, locusts were given access to multiple synthetic foods that varied in their concentration of the two most strongly regulated nutrients (protein and digestible carbohydrate) and a carbon-based PSM, tannic acid (TA). Insects in the first experiment were given two suboptimal but complementary foods: a high-protein, low-carbohydrate food and a low-protein, high-carbohydrate food. Tannic acid was then added to one food type but not the other, to both, or to neither food type. Here we could see how the addition of TA to a food with a specific protein : carbohydrate profile influenced nutritional regulatory responses. In a second experiment, locusts were given a high-protein, low-carbohydrate food and a low-protein, high-carbohydrate food, both of which contained TA. A third TA-free food containing one of five different protein : carbohydrate ratios was also provided. This experiment provided an opportunity to measure the extent to which a TA-free resource would be incorporated into the diet in relation to its nutrient content. Results indicated that the extent to which locusts regulated their protein : carbohydrate intake depended on the protein : carbohydrate composition of the TA-free foods in their environments. It was evident that TA is more effective as a feeding deterrent than as a postingestive toxin, but its effectiveness as a feeding deterrent is strongly linked to the protein : carbohydrate composition of the food in which it occurs. We discuss these findings within the context of plant defense theory and models of foraging behavior.