In 1996, many swarms of red locust, Nomadacris septemfasciata (Serville), formed in the Buzi-Gorongosa outbreak area in Mozambique. Some of these swarms migrated and crossed international boundaries, on a scale not seen since the last plague of 1929–1944.

The swarms did not breed in countries that they invaded, namely, Zimbabwe, Zambia, Botswana and South Africa. On the other hand, in Malawi, successful breeding by the swarms resulted in hopper bands. Filial generation outbreaks continued into 1997 in the breeding area, but at a reduced scale.

An analysis is made of the possible causes of the upsurges of 1996 and the likely implications to the preventive control strategy that has been the principle for red locust plague prevention.

There is need for a further comprehensive study of the Buzi-Gorongosa plains so as to understand better the factors that contribute to its high potential as an outbreak area.

In this study, Coccinella septenipnnctata was efficient in controlling Aphis gossypii populations on cucumber in the greenhouse. This efficiency was a function of the predator/prey ratio and the initial aphid density at the time of release of the predator. Prey density had a large influence on the fecundity and establishment of this coccinellid in the greenhouse.

The activities, working conditions and progress of the International Red Locust Control Service during the mid-1950s are outlined. Research programmes and results are summarised.

A socio-economic study was executed in South East Niger to determine the conditions under which a novel mycopesticide based on the fungus Metarhizium flavoviride could be introduced for locust and grasshopper control as a possible alternative reducing the use of synthetic chemicals. From the interviews, all farmers estimated locusts and grasshoppers to be one of three major pests. The survey revealed that 93.8% of the farmers conduct collective pesticide applications. About 45.5% of the farmers received support from the brigades, at least once. The remaining farmers (54.5%) were not assisted by the brigades due to a lack of pesticides. Farmers estimate that the choice of any pesticide greatly depends upon its knock-down ability (57.5%) or the numbers of cadavers found after a treatment (42.5%). Most farmers (82%) consider the government to be responsible for locust and migrant grasshoppers control. On average, farmers were willing to pay US$ 1.00 per ha per year, to protect their crops.

Austracris guttulosa in northern Australia is similar to Nomadacris septemfasciata in the southern half of Africa in having one generation per year, mainly in tall grass plains that are seasonally flooded by rainfall and flooding rivers. Locusts survive the dry season as adults and after the early rains of the wet season, oviposit in bare areas. Young offspring nymphs hatch out and feed on adjacent short ephemeral grasses while older nymphs and young adults are in taller vegetation. While locusts usually do not breed well outside tall grass plains of the source area, rain is critical to overall population increase of A. guttulosa, allowing egg and nymphal survival in the normally dry open plains south of the source area. When such rain falls, a preventive control programme is instituted, which begins with forecasts of population increase in areas receiving rain for offspring survival; any high populations found are delineated for control. While swarms within the source areas are often not controlled, those further south nearer cropping areas usually are. Austracis guttulosa does not form bands, so control is usually left until the adult stage when swarms form. Current practice involves the use of chemical insecticides, though promising research indicates that the entomopathogenic fungus Metarhizium anisopliae may form part of an integrated pest management programme in the future.

With N. septemfasciata, outbreaks seem to be related to dry periods, but the precise factors leading to outbreaks are not well understood. Until further research that allows accurate forecasting is undertaken, regular monitoring of outbreak areas and control of any bands and swarms that form will be an essential part of any preventive control programme. Both bands and swarms are present for long periods, giving ample opportunity for preventive control particularly in localities where crops are grown near outbreak areas.

Field experiments were carried out at Coimbatore, Tamil Nadu State, India, for four consecutive years (1990–94), to monitor the seasonal activity of Cotesia flavipes Cameron (Hymenoptera: Braconidae), a larval parasitoid of gramineous borers, including the sugarcane shoot borer (Chilo infuscatellus Snellen), sugarcane internode borer (Chilo sacchariphagus indiens (Kapur) and sorghum stemborer (Chilo partellus Swinhoe) (all Lepidoptera: Crambidae). The highest levels of parasitism (0.0–17.9%) were recorded on Ch. partellus followed by Ch. sacchariphagus indiens (0.0–8.3%) and Ch. infuscatelliis (0.0–1.1%). The parasitoid was collected in Ch. partellus and Ch. sacchariphagus indiens in all the four study years, whereas it was not observed in Ch. infuscatelliis during 1993–94. Parasitism rates in Ch. partellus were positively correlated with minimum temperature and afternoon RH. In Ch. sacchariphagus indiens, parasitism levels showed significant negative correlation with minimum temperature. Parasitism rates in Ch. saccharipliagus indidus larvae collected during harvest from seven sugar factory areas of Tamil Nadu State were lower in 1992–93 (0.0–1.8%) and higher in 1993–94 (0.0–3.2%) than those recorded at Coimbatore in the corresponding period (December-March). Cotesia flavipes was the only larval parasitoid recorded from the borers both at Coimbatore and the seven sugar factory areas surveyed in Tamil Nadu.

The efficacy of a field vacuum unit for the management of Bemisia tabaci was evaluated on melon (Cucumis melo L.) during two summer seasons. The tractor-mounted unit was designed to dislodge insects by blowing air from lateral vents onto the plants while simultaneously vacuuming from above. Field observations, collection of leaf samples, and hand-vacuum sampling before and after the field vacuuming were used to evaluate the efficacy of removal. Bemisia tabaci population reductions were significant (30–60%) and lasted from week to week when vacuumed weekly. Parasitoid populations were slightly affected, but were not significantly different from populations in the untreated control plot. Field vacuuming was found to be as effective as insecticide applications for the control of B. tabaci in melons.

Prospects for the biological control of locusts and grasshoppers have become much brighter during the last ten years thanks to a number of international research projects. This paper examines a number of options, including one that is ready for immediate implementation: the mycoinsecticide, Green Muscle®, based on the fungus Metarhizium anisopliae (flavoviride) var. acridum. It has been registered in South Africa and other African countries are likely to follow during 1999. Trial results on grasshoppers and several locust species have been very encouraging, and preliminary tests on red locusts show potential as well. Recent research on pheromones also points to some interesting possibilities, both when used alone and in combination with a mycoinsecticide. Finally, microsporidian protozoans and rhabditid nematodes show some promise for long-term suppression of red locust populations, but more research and development is needed to demonstrate their potential.

A tsetse-control trial was carried out in a primary forest habitat on Unguja Island of Zanzibar to assess the effect of insecticide-impregnated blue cotton screens on a population of Glossina austeni Newstead. In November 1991, screens were deployed at densities of 45–70 per km2 and the fly population was monitored monthly using sticky panels. Both female and male daily catches were not affected during the initial five months after screen deployment, but the physiological age distribution of female flies shifted significantly towards younger groups. Females were more influenced by the screens than males. The fly population was very low after the long rainy season, but increased to pre-control levels three months after the flooding of the forest floor. Thereafter, male and female apparent densities decreased, and 78–91% and 98–99% suppression was obtained for males and females respectively at the end of the 18-month intervention period. While effective control of G. austeni using blue cotton screens was shown to be feasible, it required a high deployment density and a long intervention period.

Rice yellow mottle virus (RYMV) is one of the most economically damaging diseases of rice in sub-Saharan Africa. It is found only in Africa and the surrounding islands, where it is transmitted by insect vectors such as Tricliispa sericea Guérin, Chaetocnema piala Chapius and Sesselia pusilla Gerst., (all Coleoptera) respectively within the subfamilies Hispinae, Halticinae and Galerucinae of the Chrysomelidae; Chnootriba (= Epilachna) similis Thunberg (Coleoptera: Coccinelidae); and Conocephahis longipennis de Haan (Orthoptera: Tettigoniidae). These vectors are leaf-feeders with biting mouthparts and are abundantly present on rice and grasses in irrigated lowland fields. Transmission of RYMV is mechanical as a result of feeding damage. However, the dynamics of virus spread and the role of the vector is poorly understood. A better understanding of RYMV epidemiology requires information on the distribution, biology, host range, nature of damage, and management strategies of the vectors. It is hoped that this review will be a useful source of information in the further development of integrated pest/disease management (IPM)in rice.

Experiments on the effects of KK-42, an anti-juvenile hormone imidazole derivative, on the rearing and reproduction of Bombyx mori L. were carried out in a hot, wet summer in West Bengal, India. A single dose of 3 μg KK-42/larva induced precocious metamorphosis in a bivoltine hybrid (KPGB × P5) race of B. mori when applied topically to freshly moulted (less than 1-h old) fourth instars, and increased their rearing performance over control tetramoulters. However, cocoon and shell weights, shell ratio and filament length were reduced by the anti-JH treatment. Final body weight and head capsule width of the treated fourth instars were significantly higher than those of the controls. Bivoltine trimoulter males also showed good capacity for mating with multivoltine Nistari females. The possibility of obtaining three-way multi-bi hybrid eggs during the wet part of summer in a tropical climate is discussed.

The intensity of diapause of field-collected diapausing larvae of Olilo partellus (Swinhoe) and Chilo orichalcociliellus Strand (Lepidoptera: Pyralidae) was compared in the laboratory at 28 ± 0.5°C under a photoperiod of 12:12 (L:D)h. Chilo partellus terminated diapause faster than C. orichalcociliellus. Mean time to diapause termination was 9.7 days for C. partellus and 14.4 days for C. orichalcociliellus. Male and female C. partellus larvae terminated diapause and adults emerged at the same time, while significant differences were found in diapause termination and in emergence times between male and female C. orichalcociliellus.

The outbreak areas of the red locust are seasonally inundated wetland areas supporting a rich biodiversity. The potential for environmental damage from the repeated use of broad-spectrum insecticides for locust control in these ecologically sensitive wetlands is therefore great. This paper describes the first trial of a Metarhizium anisopliae var. acridum (LUBILOSA isolate IMI 330189) mycoinsecticide as an alternative, more environmentally benign, intervention strategy for managing red locust populations in their outbreak areas. Following initial bioassay tests in the laboratory, which gave 90–93% kill of 3rd instar hoppers within 6–9 days, an oil based formulation of aerial conidia was applied at a rate of 5 × 1012 conidia/ha using a motorised ‘Solo’ knapsack sprayer to treat 3rd and 4th instar hopper bands in the Buzi outbreak area near Beira in Mozambique. Caged samples of 3rd instars succumbed quickly with a median time to kill of 3.6–3.9 days and 98–100% kill recorded within 8–9 days. The 4th instars took longer to die, with a median lethal time of 5.9–6.1days and > 90% mortality after 21 days. Mortality in control samples was low with 13–23% mortality after 21 days. During this mortality assessment period mean minimum and maximum air temperatures ranged from 26–34°C and relative humidity ranged from 85–100%. Observations on treated bands in the field showed that the cohesion of the 3rd instar bands broke down within 6 days, while controls still behaved normally. Unfortunately observations on the 4th instar band had to be terminated after 10 days due to heavy flooding. This preliminary field trial demonstrated the feasibility of using a Metarhizium mycoinsecticide, applied through conventional spray equipment, for controlling the red locust in its outbreak areas.

The aim of the present study was to determine, by a field experiment, whether the seasonal variations in the levels of cyanide and rutin in the phloem, secondary compounds potentially implicated in cassava resistance to the cassava mealybug (Phenaccocus manihoti), could be influenced by different kinds of soil fertilisation (manure, NPK, KC1, lime, mulch). It was found that mean cyanide and rutin contents varied significantly with season, soil treatments and infestation. For each soil treatment, the highest contents of these compounds on uninfested plants was registered in the main dry season (Jul-Aug) for cyanide and at the end of the dry season (Jul-Aug) and beginning of the rainy season (Oct-Nov) for rutin. The infestation factor induced an increase in cyanide and rutin contents for 43 combinations of period and soil treatment among 48 in total. For cyanide content (phagostimulant function in mealybug), this increase appeared significant at the end of the rainy season (Apr-May) and in the main dry season (Jul-Aug) for control and KC1 fertilisation. For rutin content (an unfavourable substance for the insect) significant increase was induced by infestation in each period for manure and mulch and especially in the main dry season (Jul-Aug) and at the beginning of the rainy season (Oct-Nov) for other soil treatments. Concerning the seasonal variations in the level of rutin, these results showed that mulch and manure are the best fertilisers to increase cassava resistance against mealybugs.

The historical account of the rise and fall of Nosema locustae as a biological control agent of grasshoppers has substantial implications for the successful development and implementation of biological control of migratory locusts in Africa. The potential of N. locustae was ultimately not sufficient to overcome a set of impediments, including: efficacy (the rate and extent of mortality were relatively low), target specificity (not all pest species were susceptible), formulation (wheat bran bait excluded feeding by some pests), cost (the price of the formulated product was excessive), storage (the organism lacked long-term stability), complex application (the pathogen and its carrier had to be applied during a narrow set of environmental and logistical parameters) and production (the use of an in vivo production system made high-volume production difficult). Some of the most significant limitations that led to the failure of N. locustae have been overcome by work on other pathogens, including the problems of formulation, storage, efficacy and production. However, at least four relevant lessons can be derived from the N. locustae story and applied to ongoing work with biological control of migratory locusts. First, the erratic population dynamics of acridids necessitates that the production, storage and distribution of an augmentative biological control agent will be driven by a boom-and-bust cycle. Second, the immense spatial scale and low unit value of the resources (rangelands) being protected create a unique set of logistical challenges. Third, the control of acridids involves the management of a native insect pest embedded within complex, native ecosystems, which suggests that our interventions should be undertaken with a great deal of caution, monitoring and, ultimately, humility. Fourth, although pathogens can be used as ‘bio-insecticides’, biological control requires education of end-users regarding a more sophisticated approach to pest management.

The effect of fluoride on the food and dietary water intake and utilisation were studied in final instars of silkworm, Bombyx mori L. race NB4D2 fed ad libitum with mulberry leaves treated with sodium fluoride at concentrations of 25 ppm, 50 ppm and 75 ppm. The larval duration increased by two days while food consumption, assimilation rate, assimilation efficiency, feeding and metabolic rates increased significantly in all the treated larvae. On the other hand, the amount of faeces produced, food conversion, conversion rate and conversion efficiencies decreased significantly in all the treated batches when compared to controls. The water intake and utilisation parameters increased significantly while rate of water loss through faeces, water retained in the body and retention efficiency decreased in all the fluoride-treated silkworms. The factors responsible for these changes in treated batches are discussed in relation to the effect of fluoride on cocoon and shell weights.

The red locust, Nomadacris septemfasciata (Serville) (Orthoptera: Acrididae), is a threat to agricultural productivity in Malawi. The country has a single known red locust outbreak area, the Lake Chilwa flood plains in southern Malawi, in addition to several other areas where the locust occasionally breeds. Activities of the red locust in Malawi during the period 1988 to 1998 are discussed. Four major outbreaks occurred during the period—in 1993, 1995, 1996 and 1997. Control of these outbreaks was conducted by air except for the 1995 outbreak in Mpatsanjoka River Valley which was controlled by spot treatment on the ground. The use of both a helicopter and a fixed-wing aircraft, where the helicopter locates locust swarms and their concentrations and guides the spray aircraft, appears to be the most efficient and effective strategy for controlling locust outbreaks in Malawi.

Eggs and larvae of Microplitis rufiventris Kok. (Braconidae: Hymenoptera) were exposed to two sublethal concentrations (0.2 and 0.4 ppm) of the chitin synthesis inhibitor lefenuron, by feeding treated artificial diet to their hosts, Spodoptera littoralis (Boisd.) (Noctuidae: Lepidoptera) larvae. Each concentration was initiated during the egg stage or different instars of the parasitoid larvae. Between 4.3 and 33.8% of parasitoid larvae in lefenuron-treated hosts showed morphological and developmental abnormalities. The effect of the compound on the developmental rate and sensitivity of the parasitoid larvae varied according to the parasitoids' age at treatment; the egg stage and older parasitoid larvae were more tolerant to the compound than the first instars. In all treated hosts the developmental rate of the parasitoid was lower than that of controls. The lower lefenuron concentration (0.2 ppm) was more effective at disrupting the development of young parasitoid larvae than the higher one. Delayed or latent effects of the compound were evident in non-emergence of parasitoid adults that were exposed to the compound as first instars. Reduced sensitivity of old parasitoid larvae could be compatible with survival of the parasitoid in integrated control programme of S. littoralis.

Indoor-resting blood-fed Anopheles gambicie s.l. were collected from selected localities in Ethiopia. Anopheles arabiensis was the only sibling species identified. Paracentric chromosomal inversion polymorphisms were observed on the 2R and 3R arms. A significant excess of heterozygotes was obtained in samples from Siile carrying the 3Ra inversion. Similarly, significant variation was seen in the frequencies of the 3Ra inversion between the study localities. The observed intraspecific inversion polymorphisms relative to indoor resting behaviour are discussed.