The World-Wide Magnitude of Orthoptera as Pests

Abstract

A quantitative assessment of pest status in Orthoptera s.str. is currently difficult. While estimates of crop-damage are sometimes available and relatively easy to obtain, this is rarely translated into crop-loss nor is reduction in productivity of domestic animals as a result of damage to rangelands. Crop damage rarely has a simple relationship to crop-loss. Obtaining a direct measure of harvest weight is complicated by harvest methods. Effect of prolonged attack over a number of years must be taken into account. The varying market value of the crop lost will alter the status of a pest locally. Most published annual data does not take these subtleties into account. Published government harvest loss data may be exaggerated either upwards (perhaps to get aerial spraying into an area to kill cattle ticks) or downwards (to achieve forecast government productivity targets). Most Orthopteran pests attack as associations of two or more species, each of which oscillates in numbers independently. Monitoring studies rarely continue for periods long enough to understand what drives these changes. Exceptions are to be found in the mid-west of the U.S.A. (Anderson 1970, Hewitt, and Onsager, 1982), central Asia, and eastern Australia. Long-term changes in farming practice, e.g. replacement of millet by sorghum in the Sahel, may be indirect clues that Orthoptera pest damage is having an effect. Intercrops and poor weeding may favor greater attack by acridids. Qualitatively centers of Orthopteran pest activity can be chosen. These include North America, Central America, the southern Caribbean, central and northeast South America, sahelian Africa, Ethiopian highlands, southwestern and southern Africa, eastern Europe, central Asia, northern Africa, India, East Pakistan and Afghanistan, parts of the Arabian peninsula, China, Philippines, and Australia. Severe damage is often evident where there has been displacement of farming communities during recent wars and agriculture has been abandoned. Ecological disequilibrium is more frequent where marginal lands have been occupied recently, e.g. Kenya, or arid lands irrigated (as in Libya) or overgrazing incurred (as in Central Asia) accompanied by drought. Some vegetational changes seem to be natural,