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Field infestation of millet by Sitotroga cerealella (initial infestation) has been studied in two cropping systems and in three locations in Senegal. In all cases, ears were attacked since harvest, but the level of damage was 10 times higher on ears from fields close to dwelling houses than on those away from dwelling houses. In this way, the author discusses the problematic conservation of millet seeds in farm conditions, depending on that initial infestation in one hand and on the other hand on storage method of millet ears in traditional granaries.
Observations on the fauna that live in close association with mounds constructed by Cubitermes testaceus (Isoptera: Termitidae) were made in a grassland area of Uganda. Termite nests were systematically excavated and dissected and a careful record of the fauna associated with each was made.
Arthropods belonging to three different classes were recorded in mounds of C. testaceus and with varying degrees of occurrence. They included insects (93%), chilopods (5%) and diplopods (2%). Ants were found to be the commonest insects in the mounds followed by other termites (21%) Coleoptera (9%) and Dictyoptera (1%).
In view of the carnivorous nature of most of the ants recorded, and considering the feeding behaviour observed in the field, it is suggested that they can have considerable effect on C. testaceus populations in the grassland ecosystem at Kaazi.
Part I: Symposium on Integrated Pest Management and Environmental Conservation: Insect Physiology
The stable fly, Stomoxys calcitrans L., has two pairs of Malpighian tubules. Ultrastructurally, the tubules consist of three morphologically distinct zones: the distal, intermediate and proximal regions, which themselves are characterized by distinct cell types. The tubule cells have numerous mitochondria, microvilli and basal infoldings, which are associated with mitochondria. It is suggested that the distal and intermediate regions are secretory, while the proximal region is reabsorptive; and that the haemotophagous habit in S. calcitrans is probably correlated with the ultrastructure of its Malpighian tubules.
Part I: Symposium on Integrated Pest Management and Environmental Conservation: Pest Management Strategies and Practices
A large and varied group of insects attack crops of the tropical farmer, and carry various disease-causing organisms to him and his animals. The control of these agricultural pests, and vectors of human and animal diseases relies mostly on chemical pesticides. However, investigations show that alternative methods such as biological control and resistant crop varieties are available, which may be used in the reduction of pest infestation, resulting in an Increase in food production by the African farmer.
The paper acknowledges the need for pesticide usage to boost agricultural production and for disease control in Uganda and elsewhere in Africa. But drawing from some instances of pesticide pollution so far reported in Africa, the paper highlights the need for cautious use of the chemicals in order to avoid further pollution.
The need for using pesticides within the framework of integrated pest management (IPM) is presented, but also presented are results of a survey which indicates that quantities of pesticides used continue to increase, and that the attitudes of farmers and extension workers are still heavily weighted in favour of pesticide application alone.
A number of options that could be taken to inculcate IPM ideals and concepts among the people are presented, emphasizing education and training, not only for farmers and extension workers, but also for the youths most of whom are destined to become the future farmers.
The various agricultural ecosystems in The Gambia are described in brief, and the richness of flora and fauna discussed. Indiscriminate cutting of trees without replanting, bush fires and mechanization of commercial crops have so far been much more destructive to the environment than has chemical control.
In the future one may expect more chemical control to be used in commercial crops, but probably not in subsistence cultures. With more commercial enterprises and less government participation, risks for the environment will probably increase.
The CILSS Integrated Pest Management Project (1983–1987) showed that it is possible to reduce yield losses without endangering the environment. IPM approaches can improve the methods of cultural and traditional control in subsistence cultures, and keep chemical control at a low level in commercial crops. Introduction of varieties which are tolerant or resistant to the most important pests, and biological control agents can be used for a number of crops. The system of surveillance, which was introduced for a number of pests by the CILSS project, should serve as a permanent basis for all control activities.
Commercial cotton growing in the Sudan dates from 1867. At present, about 400,000 ha of various cotton cultivars are grown under different irrigation systems. The production of this main cash crop has been faced with a multitude of entomological and pathological problems, some of which were tackled through the adoption of specific cultural practices or enforcement of legislative regulations.
When cotton treatment with synthetic organic insecticides was initiated in the mid 1940s against Empoasca lybica de Berg, the impressive preliminary results have encouraged over-reliance on chemical control at the expense of other measures. This rather limited approach of control strategy has contributed partially to the appearance of new pests in damaging levels e.g. Heliothis armigera (Hbn.), Bemisia tabaci (Genn), Aphis gossypii (Glov) and Spodoptera littoralis. The principal measure for their control is insecticide application.
The cost of crop protection soared to ten-fold during the last 20 years. The annual number of sprays applied to cotton increased from one to seven sprays. To overcome the ever increasing use and high costs of pesticides on cotton growing, the Agricultural Research Corporation undertook intensive research programmes to find answers to major crop protection problems. Since 1978 researchers are directing their efforts towards the development and implementation of integrated pest management strategies to include cultural and legislative measures, as well as the use of more selective insecticides.
The potential of plant genetics in the overall context of integrated pest control could be viewed simply as the potential of plant resistance in pest management. Genetic resistance in plants is one of the most effective and economic means of controlling plant pests. Resistant plants are the first line defence against pests. Successes in breeding for pest resistance depend upon the sound knowledge of the plant genes controlling resistance to pests.
Recent report on the existence of two nonatlelic and independent genes, Rac1 and Rac2 in cowpea cultivars ICV 10 and TVu 310, and ICV 11 and ICV 12, respectively, from the ICIPE has broadened the scope of cowpea breeding against aphid biotypes. Use of biotechnology as a plant breeding tool in transferring resistance genes into agronomically suitable cultivars appears to hold good promise for the future.
Studies aimed at setting up a system of rational control of pests were carried out at the Vallée du Kou rice irrigation scheme near Bobo-Dioulasso in 1986. The first part of the study focuses on the phytosanitary survey of the above mentioned rice irrigation scheme of 1043 ha through a network of observation sites. This part has given prominence to the fact that the development and importance of the pest infestation were affected by the spacing out of the rice planting and has also allowed us to locate the critical periods of the infestations and their economic incidence. These pests consist mainly of lepidopterous stem borers: Chilo sp., Sesamia sp., and Maliarpha separatella.
The second part of the study focused on phytosanitary experiments. Using Decis (Deltamethrin) at 12.5 g a.i. per ha at the intervention thresholds of 5% dead heart and 1% whitehead, has proved to be the most interesting formula as it combines efficiency and profitability.
The system of rational control that has been set up based on phytosanitary survey and insecticide application at threshold levels, presents a double advantage, it reduces the number and cost of interventions, and limits the anarchical use of pesticides, hence their harmful effect on the environment. Such experience in insect pest management will be extended to other rice growing areas throughout the country.
Seven species of stored grain pests were found infesting underground storage pits “bakars” in the Bay Region of Somalia. These species and their relative abundance (%) in “bakars” are as follows: Alphitobius laevigatus (Fabricius) (Coleoptera, Tenebrionidae) (3.7%), Palorus subdepressus (Wollaston) (6.1%), Tribolium castaneum (Herbst) (29.2%); Rhizopertha dominica (Fabricius) (Bostrichidae) (23.9%); Sitophilus oryzae (Linneaeus) (Curculionidae) (4.7%); Cryptolestes ferrugineus (Stephens) (Cucujidae) (32.4%); Sitotroga cerealella Oliver (Lepidoptera, Gelechiidae) (unsampled). The mean percentage damage by insects for the region was 10.4 and by rats was 8.4 for sorghum grain stored as heads in 100 “bakars”. Actellic, K-Othrine and Malathion, applied as a 2% dust to threshed durra sorghum grain stored in sacks above ground, provided 99.2, 99.5 and 94.5% control, respectively.
An initial study of the extension service and pest control in Iganga district was made between 14 July and 20 August 1987. This was part of a more extensive on-farm study of pest control problems in the district. This study covered 36 small scale farmers randomly picked from the three agricultural sub-zones in the district.
It was observed that: (i) information on crop protection was scanty, (ii) the majority of the farmers were aware of the presence of pests on their farms, (iii) there is a minimal use of pesticides on small scale farms in the district, (iv) a number of pests occur in varying frequencies on small scale farms in the district and (v) the extension staff are still too few to handle even the general aspects of crop production.
Insect pest problems on cowpeas can be reduced by use of strategies which involve ecological manipulations. These include crop diversification (mixed cropping, etc.), alteration of planting dates, crop rotation, trap-cropping and weed control. The merits of these cultural methods of pest control are discussed.
The status of biological control of cowpea pests is still low but promising. The crop is an annual and therefore offers very limited possibilities for the application of the classical biological control techniques. However, a large number of parasitic Hymenoptera, Diptera and predatory Hemiptera, notably Reduviids have been identified in the cowpea ecosystem. Ecological studies of some of these have been carried out and levels of parasitism determined in a few cases, but their significance in the dynamics of cowpea pest populations have not been fully established.
It is however known that conservation of parasites and predators in their wild environment is one of the traditional biological control methods. Therefore, a rationalized pesticide programme for the control of cowpea pests should aim at preventing hazards to their natural enemies so as to increase their biocontrol efficiency.
Ctenocephalides felis adults obtained from young goats belonging to the Faculty of Veterinary Medicine (SUA) were reared in captivity and the offsprings used for testing against permethrin. A total of 1260 fleas were exposed to 0.005% permethrin dust (0.5% a.i. diluted with fine sand) for periods varying from 30 min to 24 hr. Additionally, white rats infested with 2400 fleas were exposed to a similar mixture for 24 hr.
In the first set of tests, 100% mortality was obtained after a 2-hr exposure of the insects to the insecticide. Similarly, in the second set of tests, all the fleas were found dead at the end of 24-hr exposure.
It was generally concluded that permethrin is very effective against this flea species and that it could be used for controlling the ectoparasite in livestock, animal barns and residential houses in the area. It was finally recommended that similar tests with other flea species in the country, especially in plague endemic areas were desirable.
An experimental microspodiosis has been stimulated within Heliothis armigera (Lepidoptera, Noctuidae). The microsporidian used was Nosema manierae, a natural parasite of Chilo zacconius (Lepidoptera, Pyralidae). Nosema manierae causes high mortality in the larvae and the nymphs.
Following the introduction in Congo of the cassava mealybug, Phenacoccus manihoti in 1973, a French Congolese team was set up to tackle the problem. The main results of the team's studies that aimed to the effectiveness of Epidinocarsis lopezi a parasitoid introduced in Africa from South America by IITA, are reported here.
The studies were simultaneously developed in the laboratory and in the field, In the areas of biology, physiology, behaviour and ecology of the Encyrtidae. These studies allowed the drawing up of a balance of its qualities and limits observed, its effectiveness in natural conditions and provide the opportunity to share some ideas on the use in Africa of the South American's auxiliary. The different areas of the studies are successively examined.
Part II: Symposium on Insect Pests and Sustainable Food Production
In the years prior to independence, farmers had access to the international market through the production of export crops which at that time received considerable input from research. Access to export crops has dwindled, support for research by national governments is disappointing, human resource development is inadequate, donor funding is uncoordinated, and the food crisis has taken on political dimensions. The assumption that direct importation of western technology can solve the problems of Africa is no longer valid in the face of several failures. The challenge to national agricultural research systems and the problems associated with the generation or adapting of farmer-oriented, location-specific technologies for sustaining agricultural production are discussed. Examples are drawn from India and an agenda for action, involving national governments, the international agricultural research centres and donors, in resolving these problems is presented.
Part II: Symposium on Insect Pests and Sustainable Food Production: Ecology, Biology and Bionomics
A drop off rhythm of engorged Rhipicephalus appendiculatus Neumann was demonstrated for females and engorged nymphs, but not for larvae. Seventy per cent of 1279 engorged R. appendiculatus females dropped off the animals between 0800 and 1000 hr, while 66% of 2736 engorged nymphs dropped between 1600 and 1800 hr.
Females which were put on the animals at night (2000 hr), started to drop-off 24 hr later, than those put on in the day (0900 hr). Ticks which were fed on tick-sensitized animals also started to drop off 24 hr later, than those on tick-naive animals.
The implications of these results on tick control management are discussed.
Food plant preferences and spatial dispersion patterns of the armoured ground cricket, A canthoplus speiseri Brancsik were investigated. The average numbers of the ground cricket found feeding on each food plant per transect in each of the three study areas were tested for differences at the 0.05 level of probability by Duncan's multiple range test. The variance/mean ratio was used to analyse spatial dispersion patterns. A. speiseri fed on 12 plant species from the Compositeae, Gramineae and Solanaceae families. Hyparrhenia nyassae (Rendle) Stapf., (Gramineae) and Rottboelia exaltata Linn, f., (Gramineae), were the most preferred food plants. The armoured ground cricket densities on the two food plants were insignificantly different from each other. The cultivated plants, Zea mays L., and Sorghum vulgare Pers., were fed upon opportunistically by the ground crickets. The variance/mean ratio identified aggregation in the armoured ground cricket populations in all three study areas . The significance of the findings on food plant preferences and dispersion patterns are discussed in relation to future sampling and control of A. speiseri.
Students in the 2-year diploma course in crop protection at the CILLS (French acronym for “Permanent Interstate Committee for Drought Control in the Sahel”) Crop Protection Training Centre (Département de Formation en Protection des Végétaux) in Niger undertake laboratory or field research work on specific subjects under the supervision of resident lecturers. It is in this context that studies on the biology of the rice armyworm, Mythimna loreyi, were conducted in the laboratory on two host plants, maize and sorghum. The studies were conducted at a mean temperature of 27.01°C and mean r.h. of 41.65%. The egg-laying habits of the insect and parameters such as the length of the preovipositional period, larval and pupal developmental period and longevity of adults were studied. Larval developmental time was significantly shorter on maize than on sorghum, but there was no significant difference in the length of the pupal period. The preovipositional period ranged from 1 to 8 days with a mean of 4.32 days. There was no significant difference between the longevity of adult males and females.