A detailed analysis of a
Desert Locust Upsurge in Saudi Arabia
(Nov 1996 - May 1997)
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(14kb) The 1996/97 winter period was a classic example
of Desert Locust upsurge: as a result of several
successive falls of rain, good breeding conditions
persisted for nearly six months which led to a
dramatic increase of locust numbers on the northern
Red Sea coastal plains of Saudi Arabia. The most
rapid surge occurred during March and April which
corresponded to a second (and heavier) generation
of breeding and reports of incoming mature swarms
from Sudan. Infestations were present from March
onwards at hundreds of locations, extending along
the coast for about 900 km. Average infestation
levels (the percent of green vegetation in which
locusts are present) were about 8% but varied from
1-30%. The initial build-up of locust numbers was
missed during the first four months (November -
March) because adults were scattered along the
coastal plains and foothills and often were not
reported by locals. It is not only extremely
difficult to accurately monitor the entire area but
impossible to treat such low densities of locusts
scattered over such a large area. First generation
breeding occurred over a long period of time and
was not well syncronized which led to different
sizes and types of populations. This was compounded
by large expanses of green vegetation which
encouraged a general increase in locust numbers
rather than concentrate the infestations. Hence,
good control targets in which high numbers of
locusts could be treated in small concentrated
areas did not really exist until the end of the
season when vegetation began to dry up. This was
after several periods of breeding had occurred. By the end of May, some of those adults that
escaped control or could not be treated moved off
the coastal plains into the foothills and the
larger valleys just beyond the first range of hills
east of Al-Wajh, Yanbu (W. Fagir) and Khulais. Only
low numbers of solitary immature and maturing
adults persisted in the few areas of green annual
vegetation (Panicum and Diptergium
sp.) and perennials (Acacia sp. bushes and
trees) in low-lying areas and wadis on the plains.
There were a few areas where groups of late instar
hoppers were present, most notably north and east
of Al-Wajh. Operations continued near Khulais,
Rabigh and Al-Wajh. However, aerial and ground
control operations steadily declined and teams were
reduced in all areas and by mid June, the campaign
had come to an end. The LCC mobilised its resources which peaked in
late April with more than 70 ground teams, four
aircraft and 340,000 litres of pesticide. Given the
difficult circumstances, the LCC significantly
reduced the level of infestations. Only a few small
swarms and adult groups mixed with solitarious
adults migrated from the coastal plains to the west
and east during May and early June. Consequently,
the campaign was able to prevent the formation of
large swarms that could have threatened adjacent
countries and extend the upsurge to other
regions. calendar
of breeding
(14kb)
