A morphological diversity study was conducted on African rice gall midge Orseolia oryzivora Harris & Gagné and two other African species, Orseolia bonzii Harris and Orseolia nwanzei Harris & Nwilene, sp. n. Morphological differences between adult and immature stages of the three species are slight and mainly evident in pupal characters. Due to limited differences in morphological characters, genomic DNA fingerprinting of these three insect species was carried out using random amplified polymorphic DNA (RAPD) and sequence-characterized amplified region (SCAR) methods. Out of 90 operon primers, 15 showed polymorphism among the three species tested, generating 86 bands, 60 (70%) of which were polymorphic. Primer OPV6 produced three RAPD markers that distinguished the three Orseolia species. These markers were cloned and sequenced. Their sequence was then used to design six SCAR primer pairs. Each SCAR primer pair amplified and distinguished the three Orseolia species at genomic DNA level. Both SCAR and RAPD genomic DNA fingerprinting revealed that O. oryzivora and O. bonzii are most closely related and O. nwanzei is distinct. Each of the six SCAR primer pairs produced a specific DNA fragment size specific for O. nwanzei, O. oryzivora and O. bonzii. The DNA fingerprints will be useful for entomological survey, identification of new species and differentiating aggressive from non-aggressive species, aimed at the effective development of rice cultivars with durable resistance to African rice gall midge.

Six distinct biotypes of the Asian rice gall midge, Orseolia oryzae (Wood-Mason), have been characterized so far from different parts of India and their geographical distribution has been well mapped and monitored annually through the national gall midge biotype studies. These studies have been showing minor changes in the virulence pattern of the pest population at Warangal in Andhra Pradesh state since 2000. Hence, a sample of the pest population from the site was collected during 2003 and selected subsequently in a greenhouse through 13 successive generations for virulence against diverse sources of plant resistance. This Warangal-derived population (WDP) was tested to record reactions of two sets of differential rice varieties used for biotype detection and known to carry one of the 10 known gall midge-resistance genes. The results revealed that WDP has acquired virulence against CR-MR1523, one of the biotype differential rice varieties, which derived resistance from the source Ptb21 cultivar. Since the virulence pattern noted for WDP was different from that noted for the six characterized biotypes, it is proposed to designate this new biotype, tentatively, as biotype 4M. Only three of the resistance genes, viz. Gm3Gm4 and Gm8 confer resistance against this biotype.

Pitfall-trap sampling was used to determine the activity (numbers collected as determined by locomotor activity and density) of epigaeic (soil-surface dwelling) arthropods in rice cultivated at various toposequence sites on the slope of an inland valley in Bouaké, Côte d'Ivoire, West Africa in 1994–1996. The major arthropod groups collected were ants, spiders, crickets, carabids and grasshoppers. Ants and spiders were the most active. Arthropod activity changed in response to crop growth stage with activity generally increasing towards harvest. Ant activity differed significantly between toposequence sites and was highest in the upper portion of the slope. The pattern for spider activity in relation to toposequence site varied among years. Agronomic practices that would enhance the populations of ground-dwelling predaceous arthropods are an important consideration when developing cultural practices for rice production on hillsides of inland valleys in West Africa.

A ‘rice garden’ with monthly plantings of rice was established in an irrigated lowland area in April 1993 and continued for 3 years. Populations of the most common insects, the stalk-eyed flies, Diopsis spp., and the green leafhoppers, Nephotettix spp., and spiders and stemborer damage varied distinctly in relation to month of transplanting. Arthropod populations also exhibited distinct patterns in relation to crop growth stage. Grain yields varied with month of transplanting but there was no distinct trend from one year to the next. This study indicated that continuous cropping of the same fields over a 3-year period did not result in a build-up of insect pests or a decline in grain yield.

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.

Populations of larvae and pupae of the African rice gall midge, Orseolia oryzivora Harris & Gagne (Diptera: Cecidomyiidae), and two parasitoids, Platygaster diplosisae Risbec and Aprostocetus procerae (Risbec)[= Tetrastichus pachy diplosisae Risbec], were recorded in replicated experiments on farmers' fields at Karfiguéla, Burkina Faso in the 1992 wet season and the 1993 dry season. In each season, four plantings were made at 14-day intervals and samples taken at weekly intervals for 10 weeks. Gall midge populations in the wet season developed through three distinct phases: an initial slow increase, followed by a period of rapid increase coinciding with maximum tillering, and then a final decline. On average, the highest midge populations and highest levels of parasitism developed in the later plantings. During the dry season midge infestations were low and no parasites were detected.

The effect of protein fractions isolated from cereal grains on the development and survival of the bean weevil, Callosobruchus maculatus, was investigated using wheat, rice and maize. These cereals were fractionated into albumins, globulins, prolamins, glutelins and a residue. The fractions were incorporated in artificial seeds which were infested by C. maculatus. Survival (as indicated by LD50) and development (as indicated by WD50) of 20-day-larvae of the bruchid were negatively affected by most of the fractions. Rice globulins were the most detrimental and affected both the survival and development of the larvae, while wheat albumins and globulins had a stronger effect on larval development than on survival. A previously isolated maize α-amylase/trypsin inhibitor showed an LD50 of 1.5% to Callosobruchus maculatus.

Seven-day-old seedlings of 22 rice cultivars with dominant Glh1, Glh2, Glh3, Glh5, Glh6 and Glh7 and recessive glh4 genes were evaluated for resistance to the green leafhopper (GLH), Nephotettix virescens (Distant), in a no-choice seedling test under uniform infestation at four nymphs per seedling. “IR29” (gene not identified) was the resistant check, while “Taichung Native 1” (no resistance gene) was the susceptible check. Maximum reproducibility for resistance score was obtained 11 days after infestation. “Pankhari 203” (Glh1), “Kalimekri 77–5” (IRRI Accessions 6613 and 6622) (Glh1), “ASD7” (Glh2), “DNJ97” and “Arai” (Glh3), “ASD8” (Glh5), “PTB18” (Glh6), and “Laki 65” (IRRI Accession 6622) and “Lasane” (Glh7) showed consistently resistant reaction under the no-choice test. The lines could be used for allelic studies of GLH resistance and for gene pyramiding.

Larval and adult predators comprise the largest component of the natural enemy fauna which attack the semi-aquatic rice caseworm Nymphula depunctalis (Guenée). Spiders, birds, and adult dragonflies/damselflies were the dominant predators of caseworm adults, while aquatic beetle larvae, aquatic bug nymphs and adults, and ants preyed on caseworm larvae. Egg parasitoids are unknown in nature and larval/pupal parasitoids are rare. A nuclear polyhedrosis virus, the only recorded pathogen, occurs but rarely. A ricefield pulmonate snail Lymnaea quadrasi (Mollendorff), which forages on algae, causes limited caseworm egg mortality in a passive and fortuitous manner. Water beetles—the dytiscid Cybister tripunctatus orientals Gschwendtner and hydrophilid Sternolophus rufipes Fabricius—are voracious larval predators. Prey consumption by these water beetles is higher on older caseworm larvae whose larger size creates more movement while the larvae are crossing the water surface. Also, older caseworms are more prone to leave the protection of their cases while under attack. Younger caseworm larvae, however, tend to retract and remain motionless when attacked. The last instar dytiscid preyed on an average of 11.4 caseworm larvae per day while that of the hydrophilid preyed on 6.7 larvae per day.

A total of 2256 germplasm accessions, 3000 advanced generation breeding lines and 150 released varieties of rice were screened under artificial infestation in the greenhouse. Among these, 15 new germplasm accessions, 50 breeding lines derived from 16 crosses and 15 released varieties were resistant. Antibiosis was the predominant resistance mechanism; antixenosis affecting oviposition was noted in 33 resistant varieties. Biochemical composition of a set of resistant varieties along with susceptible checks, revealed that nitrogen content of seven test varieties was significantly higher than that of the susceptible checks, while in other six varieties it was lower than the checks. Similarly, eight of the resistant varieties had considerably higher percentage of polyphenolic compounds in basal stem portion, but seven other cultivars showed significantly lower concentration as compared to susceptible checks. Thus, it was apparent that there was no clear trend among the resistant cultivars as a group in relation to quantitative differences of chemical components analysed.

When reared in the greenhouse, the rice skipper, Pelopidas mathias (F.) (Lepidoptera: Hesperiidae), laid 2–3 times fewer eggs than Held collected females held under the same conditions. Adult-emergence and mating/oviposition cages may have to be placed in environmental chambers with controlled temperature and photoperiod to achieve normal mating and oviposition. Rearing required a mating'oviposition-cage at least 3 m3 in volume and honey as sustenance. Eggs and larvae were held in larval rearing cages and pupae were removed and held in adult emergence cages. Maximum oviposition occurred at dawn. The total developmental period from egg to adult was 34.7 days. P. mathias demonstrated a greater oviposition preference for rice and Paspalum conjugatum Berg, than for Dactyloctenium aegyptium (L.) Willd. P. mathias successfully developed to adulthood on all 24 species of Poaceae tested, exclusive of rice, but did not survive on the six species of Cyperaceae tested. Low populations of P. mathias in rice can be attributed to its low fecundity, wide host range, and equal adaptability to upland and lowland environments, thus diluting its number.

Chilo species constitute one of the three major lepidopterous rice stem borers in Africa and their occurrence stretches across the different rice ecosystems; two major species, C. zacconius Bles. and C. diffusilineus (J. de Joannis) are found in West Africa, while C. partellus (Swinh.) and C. agamemnon Bles. appear to be the predominant species on rice in East and North Africa, respectively. A brief note is given on some aspects of the biology, especially the life history and behaviour of C. zacconius. Control measures are discussed as well as an integrated approach towards management based essentially on growing resistant varieties, conservation of natural enemies and adjusting planting dates.

Stem borers are major insect pests of rice in Africa. The utilization of varietal resistance in the management of these pests, has great economic potentials, as it involves no extra cost to the farmer and is also free from environmental hazards. Investigations into the sources of resistance to the African rice striped borer, Chilo zacconius, some possible factors associated with host plant resistance and the benefits derived from growing resistant varieties are briefly reviewed.

Several species of Chilo are serious pests (stem borers) of sorghum, maize, rice and sugar-cane. Studies on genetics of resistance to Chilo species have been carried out only In a few cases. In maize and sorghum resistance to C. partellus, measured in terms of leaf-feeding, dead hearts and stem-tunnelling is polygenic. Both additive and non-additive gene effects are important in the inheritance of resistance to C. partellus. However, the importance of additive and non-additive gene effects in determining resistance, varies with the resistance parameter in two crops. Resistance to leaf-feeding and stem-tunnelling is governed predominantly by additive genes, while both additive and non-additive genes are important in the inheritance of dead hearts. The non-additive gene action, however, is of higher magnitude and more important in the inheritance of resistance to dead hearts in maize than that in sorghum. Recurrent selection using S1, S2 lines would be efficient in increasing levels of resistance both in sorghum and maize. Tolerance should be considered as an important factor in sorghum breeding for borer resistance.

The level of resistance in rice to C. suppressalis is low to moderate and appears to be under polygenic control. A recurrent selection programme using male sterile lines could be effective in improving the level of resistance. No information is available on genetics of resistance to Chilo spp. in sugar-cane.

Pure line populations of brown planthopper, Nilaparvata lugens (Ståi), are needed for identifying new genetic sources of resistance. Among the known N. lugens biotypes in the Philippines, Biotype 1 can infest rice cultivare which lack genes for resistance. Biotype 2 can damage cultivars carrying Bph1 resistance gene, in addition to those that are susceptible to Biotype 1. Biotype 3 can infest rice cultivars carrying bph2 resistance gene, in addition to those susceptible to Biotype 1. In the greenhouse Biotypes 1, 2, and 3 are maintained on TN1 (no resistance gene), Mudgo (Bph1 gene) and ASD7 (bph2 gene) rice plants, respectively. Because Biotype 1 population is reared on TN1 plants, susceptible to all the three biotypes, accidental infestations of Biotype 1, Biotype 2 and Biotype 3 cannot be ruled out.

N. lugens biotypes were separated from each other by their differential ingestion and assimilation of food on different susceptible and resistant rice cultivars. A homogeneous population of Biotype 1 of N. lugens was produced from single pairs of males and females selected on the basis of their low food intake on rice cultivars Mudgo and ASD7. The purity of such Biotype 1 population was further demonstrated for three generations based on differential nymphal growth and development and adult longevity and fecundity on resistant Mudgo and ASD7 and on the susceptible TN1 rice cultivars. The technique can also be useful in identifying biotypes of other sucking insect pests.

The rice plant is an extremely versatile crop that is grown under both tropical and sub-tropical conditions in various ecological conditions. Several insect pest species attack the rice crop at all growth stages while in the field. The nature and magnitude of crop loss due to insect pest attack in tropical and sub-tropical Africa are highlighted. Reliable evaluation techniques for establishing relation between insect pest intensity/damage and crop loss are outlined. Natural insect pest infestation in the field, manipulation of pest infestation with chemicals, caging to confine or keep out insect pests and the use of resistant varieties as methods of estimating on-farm losses due to insects are discussed. In tropical Africa, the major constraint to the determination of crop loss due to insect pests of rice is research-related.

This bibliography on rice leaffolders contains 886 published and unpublished references for the period 1854 to June 1987. References are arranged alphabetically by the name of author and also classified by subjects. A distribution map, tables of alternate host plants, outbreaks, resistant rice varieties, resistant wild rices, natural enemies and developmental stages, and a brief description of current status of the leaffolders are also provided.

Major rice stem borers in W. Africa were discussed and scientific investigations relating to varietal resistance were reviewed. Impediments militating against a faster rate of development of this area of research in W. Africa were highlighted. A call was made to accord greater emphasis and priority to research on varietal resistance since in the long run it will become the most important rice crop management tactic feasible for the majority of West African small scale rice farmers.

This bibliography on diseases of insect pests of rice contains 287 references. Major groups of insect pathogens are briefly discussed. Available records on diseases, insect hosts and locations of collections are tabulated. Additionally, references are grouped by subject.

A new technique of mass-screening rice seedlings for resistance to the crab, Sesarma huzardi, developed by the West Africa Rice Development Association (WARDA) at Rokupr is described.

About 500 mangrove swamp local collections and a few exotic varieties have been screened for resistance to crab damage. Only 2% of the varieties have been identified as highly tolerant. Generally, the local collections were tolerant, while none of the foreign introductions have been tolerant.

The basis of resistance appears to be morphological, which physically affects feeding mechanism; thus, some varieties were more susceptible to crab damage than others.

Degree of the heritability (hb2 = 61%) estimate indicated that there is genetic variability for tolerance. In a team-oriented research, some of the varieties are being used in the WARDA breeding programme at Rokupr.