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NOVEMBER 1996.Solitary adults were first reported on the Red Sea coastal plains in November 1996. The origin of these adults is thought to be from those escaping control operations against hopper bands and adult groups in the interior of Yemen during the autumn. Most of the adults were probably drawn into the Red Sea Trench on southerly winds associated with a strong and persistent depression over the northern Red Sea in mid November 1996. The majority of these landed on the coastal plains of Saudi Arabia and probably dispersed over a wide area from Al-Lith in the south to Al-Wajh in the north, making it difficult to find them. JANUARY 1997. Small scale breeding first occurred shortly after the rains, primarily near Al-Lith and Badr, producing a new generation of solitary adults that appeared from late January onwards. Densities were still relatively low, mostly from 1-3 per ha with a few locations reporting up to 100 per ha.
In mid January, widespread light to moderate rains fell on the coast north of Jeddah. Adults may have concentrated in this area over the next few weeks, increasing in density to nearly 1-2 adults per m2 (10,000/ha) which was probably enough to induce a partial phase change from solitarious to transiens. Laying occurred by solitary adults in the Khulais and Badr areas shortly after the rains.
FEBRUARY-MARCH.Heavier laying by solitary adults and groups of transiens occurred in late February in Al-Lith, Usfan-Tuwwal, Khulais, Rabigh, and during the first half of March in Usfan-Tuwwal, Masturah, Badr, Yanbu, and Umm Lajj. Breeding during the latter period was supplemented by low density mature swarms reportedly coming from the western shore of the Red Sea on 8-15 March. The swarms were estimated to vary in size from 5-50 km2 with densities of 5-20 adults/m2 and laid upon arrival. Other laying adult densities were estimated to be about 2-5/m2. Consequently, locust numbers rapidly increased during this period.
MARCH-APRIL.High density hatching commenced about mid March and increased over the next few weeks in all areas. This led to large numbers of hoppers and, in some cases, grouping and small band formation during April. By the end of April, hoppers were fledging and new adults started to appear.
Another period of laying occurred in early April which was primarily concentrated on the northern coast near Yanbu, Umm Lajj and Al-Wajh as well as further south near Khulais. This was probably associated with late maturing adults of the incoming swarms combined with adults produced locally earlier in the year. Those in the north were not reported by locals who collect them for selling. Densities of laying adult groups were probably higher in northern areas than near Khulais and estimated to be about 5-20/m2. Hatching occurred in late April and new adults started to appear by late May. Fourth and fifth instar gregarious hopper groups were present near Al-Wajh on 28 May at densities up to 50 per m2.
MAY.By early May, vegetation was rapidly becoming dry on the coastal plains. As a result, immature adults were concentrating in the few remaining green areas along the base of the foothills. Some adults had moved up the valleys of the foothills east of Khulais and Al-Wajh.
JUNE.As a result of the control operations of the previous months, only small adult infestations were present. In response to the dry conditions and high temperatures, these migrated off the coastal plains west towards the interior of Sudan. A few of these also moved east towards the interior of Arabia.
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