Tree locusts-Anacridium melanorhodon melanorhodon, Anacridium melanorhodon arabafrum, Anacridium wernerellum, Anacridium aegyptium
Fig. 113. The distribution of Tree Locusts.
Figure 113 shows the areas where Anacridium species are found in Africa and Arabia. Anacridium melanorhodon melanorhodon, A. melanorhodon arabafrum and A. wernerellum are illustrated in Plate 3.
This species is generally found in areas of short grass and scattered trees, the most common trees in such habitats being various species of Acacia, but it may also be found in treeless areas. Of the two subspecies, A. melanorhodon melanorhodon occurs in the western part of the distribution area and A. melanorhodon arabafrum in the eastern, but the two subspecies meet in Ethiopia and Sudan.
This species is mainly found to the south of A. melanorhodon in areas where there are more trees, but the two species overlap considerably.
This is the Egyptian Tree Locust. It occurs in countries around the Mediterranean and in the Middle East.
The life cycle of Tree Locusts is similar to that of the Desert Locust except that the males generally have six instars and the females usually 7-8 or, more rarely, 6 or 9. The extra instars are quite common in both swarming and non-swarming Tree Locusts.
There is little definite information on the duration of the various stages of the life cycle but Table 13 gives some idea of the time taken for egg and hopper development. Breeding occurs during the rainy season and there is usually only one generation each year, but as in other locusts development is influenced by the weather and food supply.
A. melanorhodon melanorhodon
A. melanorhodon arabafrum
Immature adults are grey, sometimes a little brownish, brighter in younger, and duller in older individuals; in the latter a pinkish tinge is present at the base of the hind wings. In swarming adults this pinkish colour appears quite early, a month or so after fledging. Non-swarming adults are somewhat browner than swarming ones and the pink coloration may not develop until maturation.
Maturation takes place at the start of the rainy season. Mature adults cannot be distinguished from immature adults by colour alone. The only certain way to recognise a mature female is by dissection. The presence of yellow yolk in the eggs, whatever their size, is a sure sign of maturity.
Copulation and laying are much the same as in the Desert Locust except that the copulating pairs are mostly in trees or bushes until egg laying begins. Laying usually takes place at night. The eggs are laid in moist, usually sandy, soil in the form of an egg pod similar to that of the Desert Locust. The average number of eggs in a pod is high, about 150. Whether swarming Tree Locusts, like Desert Locusts, lay fewer eggs than non-swarming ones is not known. Females can lay up to three pods.
Gregarious hoppers of Tree Locusts are yellow with black markings, the pattern being different in detail for each species; solitarious hoppers are green with white and black dots. It is not unusual to find solitariously coloured hoppers amongst gregariously coloured ones, and vice versa. Various intermediate colour forms are also quite common.
After hatching hoppers climb the nearest bush or tree and may form groups. Where laying has been concentrated groups may be found over many hectares. Feeding occurs at night.
Adults form swarms which are usually both smaller and less mobile than those of the Desert Locust. During the day adults normally roost in trees, and if disturbed they will fly from branch to branch or to a nearby tree. Such disturbance, however, does not cause mass departure. Swarms usually fly at night, a habit which has earned them their Arabic name, Sari el leil, which means the 'night wanderer'. Flight usually starts soon after sunset when mass departure from the roosting sites occurs. It is in stratiform formation.
There is little information on how far Tree Locust swarms can fly because none has ever been followed. They probably settle fairly soon and begin to feed. If trees and bushes are available they settle on them, but they settle on herbaceous crops if there are no taller plants, and eat them. Feeding on crops is most likely during the dry season.
Seasonal movements and breeding
Little is known about the seasonal movements of the various species of Tree Locust. There are records which suggest that swarms of A. melanorhodon melanorhodon can move considerable distances during the dry season. For instance, it seems likely that swarms gradually moved eastward from northern Nigeria into eastern Chad between February and June 1956 and individual locusts have been caught at sea up to 100 km off the West African coast.
Anacridium melanorhodon melanorhodon breeds in an area where there is a well-defined wet season between June and October, during which breeding occurs, and a long dry season lasting from November until May. Records show that this breeding area is smaller than the overall distribution area. There is only one generation per year. Anacridium melanorhodon arabafrum occurs in areas of East Africa and Arabia where the rainy seasons are much more complex and variable. Hoppers of this subspecies have been recorded for every month between October and May. It is probable that there is only one generation a year, but it is possible that in some areas there may occasionally be two. Anacridium wernerellum has one generation per year in Nigeria where it survives the dry season as an immature adult, but two generations have been observed in Tanzania.
Further studies in the field are needed to increase the sparse knowledge of the seasonal breeding and movements of Tree Locusts.