CHAPTER ONE
1.0 INTRODUCTION
Grasshoppers and locusts include
insects in different families belonging to the super family Acridoidea
and the order Orthoptera Grasshoppers and locusts are distinguishable
from other orthopterans primarily on the basis of their external
morphology. The most obvious and distinctive features of grasshoppers
and locusts are their enlarged hind legs and their relatively short and
thick antennae. There are more than 350 grasshopper and locust species
recorded from the Sahel (Mestre, 1988), of which about 30 are considered
to be of regular or irregular pest status (Popov, 1988). Grasshoppers
and locusts occur in a wide variety of habitats, from low-elevation,
hot, dry deserts to high-elevation, moist environment. Most species
occur in arid and semi-arid environment, and it is in the warm semi-arid
and arid desert grasslands that grasshopper and locust species
diversity and population densities are the greatest They are relatively
large, active insects and require structurally open habitats where they
are free to move, and where sunlight levels are high enough to enable
them to maintain high metabolic rates. Habitat specificity varies
considerably among species of grasshoppers and locusts. Some species
such as SchistocercagregariaForskål and Oedaleussenegalensis Krauss
(Orthoptera: Acrididae) are typically common in desert environments but
can be found in a wide variety of habitats over wide geographic and
altitude ranges when outbreaks occur. Other species are much more
restricted or specific to particular types of habitats .Grasshoppers
tend to feed on particular plants that occur in their preferred
habitats.
1.1 OTHER LOCUSTS AND GRASSHOPPERS
Other important locust and grasshopper species occur mainly in Africa, but also in the Middle East. They include among others Zonocerusvariegatus L. and Kraussariaanguilifera Krauss (Orthoptera: Pyrgomorphidae); the Egyptian grasshopper AnacridiumaegyptiumL., CataloipusfuscocoeruleipesSjostedt,DiabolocatantopsaxillarisThunberg, HieroglyphusdaganensisKrauss, the brown locust LocustanapardalinaWalk, the red locust NomadacrisseptemfasciataServille, Kraussellaamabile Krauss, Pyrgomorpha cognate Krauss
(Orthoptera: Acrididae). Some of these locust and grasshopper species
may cause severe economic damage to crops while others may occur usually
only in small numbers, rarely causing heavy damage and having no
economic importance.(COPR 1982)
1.2 HOST PLANTS AND ECONOMIC IMPORTANT OF GRASSHOPPERS AND LOCUST
Both
grasshoppers and locusts cause direct losses to crops by voraciously
devouring vegetation. They feed on several economically important crops
among which rice, wheat, cotton, maize and millet are the most
important. Some species are host specific to certain plants; others feed
on many different species and even families of plants. Total plant loss
may occur when attack coincides with vulnerable stages of the crop.
Grasshoppers pose damage every year, but become very destructive during
outbreak periods. In the Sahel and Sudan savannah zones of West Africa,
the Senegalese grasshopper O. senegalensisisan important pest of Pennisetum (millet),
the principal food crop of the region (Cheke et al; 1980). In outbreak
years, hopper bands can destroy millet and sorghum seedlings and farmers
often have to reseed several times. In 1989, 5.7% of the farmers in
northwestern Mali lost 70 to 90% of their millet crop due to
grasshoppers (Cheke, 1990; Kremer and Lock, 1992). In Niger, between 10
and 82% damages measured on millet seed heads have been reported to be
caused by O. senegalensis (Cheke et al., 1980).
1.3 MANAGEMENT AND CONTROL OF GRASSHOPPERS
Chemical
control strategies Control of grasshoppers and locusts has
traditionally relied on synthetic insecticides and for emergency
situations this is unlikely to change. Large-scale locust and
grasshopper outbreaks generally demand immediate attention and
significant short-term reduction of the pest populations. To prevent
total crop losses following severe outbreaks, chemical controls with
conventional pesticides have been the most appropriate strategy in
Sahel, Northern United States and Canada, South-eastern Asia, Australia
and elsewhere from the 1950s to the mid-1980s (Brader, 1988). The
technique of control of locusts and grasshoppers involved the spraying
of barriers of persistent oregano chlorine insecticides across areas
infested by hopper bands. For many years, the product of choice was
dieldrin, a persistent pesticide well suited for barrier treatment
(Brader, 1988). However, concerns about its detrimental impact on the
environment resulted in its prohibition in most countries. Since the
withdrawal of dieldrin, locust and grasshopper control has become more
difficult and less efficient. In the absence of this product, other less
persistent pesticides such as fenitrothion, malathion and fipronil,
have been used for acridids control in Africa and in many parts around
the world targeting both nymphs andadults. They are sprayed or dusted
directly onto hopper bands and swarms, or distributed close to them as
baits. All of these techniques require much greater effort in locating
and treating individual targets than the former barrier technique that
had been apparently successful. Most modern pesticides such as
fenitrothion that has a half-life of about 24 hours are much less
persistent and have therefore to be applied more frequently in larger
volumes. Hence, even though they are less toxic than dieldrin, their
environmental impact may well be worst. The scale and cost of pesticide
application added to the concerns over the environmental and human
health implications have triggered a strong interest in international
programs for the development of microbial control agents for use in
integrated control of acridoid pests. Biological control as alternative
to conventional pesticides Biological control of acridoid pests has
been developed as an alternative to conventional chemical application.
At least 200 species of insects, mites, and nematodes attack
grasshoppers. Various species of flies and wasps parasitize grasshopper
nymphs and eggs while other flies, beetles (including blister beetle
larvae in the genus Epicauta), birds, and rodents are
significant predators. Among diseases that occur naturally in locust and
grasshopper populations, the most common are from fungal infections and
microsporidian, principally Paranosema locustae Canning (Micro
sporidia: Nosematidae) (Brader 1988)
1.4 OBJECTIVES OF THE STUDY
The objectives of the study are
(i) To determine the food plantpreferred by Oedaleus species as host plants.
(ii) Tofind out the effect of neembiopesticide on grasshoppers
(iii)Determine the duration of development of larval instars
(iv)Treat food with neem extract and record the behavior of the grasshoppers