FOOD PLANT PREFERRED BY OEDALEUS SPECIES

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 plant preferred 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