Schistocerca gregaria (Forskål, 1775)

Schistocerca gregaria (Forskål, 1775) View in CoL

Figs 32 View Figure 32 , 33 View Figure 33

References for Socotra.

Popov (in Uvarov and Popov (1957)): 375; Popov 1959: 89–95; Wranik 1998: 161; Wranik 2003: 322, plates 152, 156.

Diagnostic notes.

This large, fully-winged grasshopper is light brown and subtly patterned with minor dark spots. The pronotum is saddle-shaped and constricted in the prozona. The median external area of the hind femora bears a thin longitudinal blackish line in the centre (Fig. 32 View Figure 32 ). The subgenital plate is deeply bilobate.

Taxonomic notes.

Schistocerca Stål, 1873 is a species-rich genus from the Americas with a single ancestor from the Old World, Schistocerca gregaria ( Song et al. 2017; Hemp and Rowell 2020).

Distribution and occurrence.

Schistocerca gregaria occurs in Africa and Southwest Asia ( Hemp and Rowell 2020), including Socotra (Fig. 32 View Figure 32 ). Both the solitary and swarming phases occur on the island. Records of solitary specimens are relatively scarce. Orthoptera expeditions before 1953 did not record the species ( Uvarov and Popov 1957). When Popov worked on the island in 1953, the species was mainly in the gregarious phase. He recorded only two adults of the solitary phase at Noged, the coastal plane in the south. The Oxford expedition in 1956 collected only one specimen ( Popov 1959). Wranik recorded a handful of specimens during his trips ( Wranik 1998). In 2009, we only recorded (and collected) one specimen. In 2010, we only did one sight record at Erisseyl (Fig. 33 View Figure 33 ).

Habitat and biology.

Popov (1959) reported three swarming events of Schistocerca on Socotra: in 1942, in the winter of 1950–51 and in the winter of 1952–53. In the latter, the initial arrival of the swarm and the following egg-laying were expected to have occurred between early December and mid-January. At those times of the year, rains ensure moist conditions suitable for egg-laying. Egg-laying occurred over most parts of the island, mainly on the coastal plains and higher in the Hagher. The first fledging was reported on 20 February and lasted until the first week of March. Few areas of the island were clear of hopper bands, except the dry western parts. After operations to wipe out the heavy infestation, survivors moved high into the Hagher, forming a huge swarm measuring many square miles. After 23 March, the swarm left Socotra, presumably to Somalia ( Popov 1959).

The origin of all three known swarming events is expected to be connected to outbreaks in India and Pakistan and the subsequent movement towards the southwest, to southern Iran, the Arabian Peninsula and Somalia. The swarms on Socotra could have crossed from Arabia or even originated directly from India. Although the species occurs on Socotra in the solitary phase, according to Popov (1959), the circumstances on the island seem unfavourable for the development of the swarming phase there itself. It is unclear if this is still the case.