Francis E. Nwilene

Efficacy of traditional practices and botanicals for the control of termites on rice at Ikenne, southwest Nigeria

Upland rice is mostly at risk from soil-borne insect pests, including termites, which cause significant crop yield losses. Studies were conducted in 2005 and 2006 at Ikenne, southwest Nigeria to assess the effectiveness of two traditional practices (cow dung and red palm oil mixed with pawpaw), two plant extracts (neem seed oil and neem powder) and Furadan coated with garri (cassava flour) against termite attacks on nine rice varieties—NERICAs 1–7, LAC 23 and OS 6. In 2005, the results showed that neem seed oil was more effective than neem powder and cow dung in the control of termites. Of the five treatments in 2006 (Furadan coated with garri, neem seed oil, neem powder, cow dung and red palm oil mixed with pawpaw), two treatments—neem seed oil and Furadan coated with garri—gave the best protection against termite attack. Among the rice varieties, termite attack was significantly lower on NERICA 5 than on the other NERICA varieties in both years. NERICA 5 was apparently the least attacked by termites when unprotected, indicating that it could be used as a resistant check variety for termites. Yield losses were lower in the treated than in the control plots. These findings indicate that botanicals, such as neem seed oil, can provide effective control against termites on rice fields and can also be used as alternatives to persistent chemical pesticides. This study has far-reaching implications because neem seed oil is environmentally safe, easy to prepare, readily available and affordable by resource-poor farmers in Nigeria.

Biology of the African rice gall midge Orseolia oryzivora (Diptera: Cecidomyiidae) and its incidence on wet-season rice in Nigeria

The biology of the African rice gall midge Orseolia oryzivora Harris and Gagné was investigated in screenhouse and laboratory studies, and its incidence on cultivated wet-season rice was studied in farmers’ fields during the 2006 and 2007 rice-growing seasons at two localities in Nigeria. This insect is nocturnal, and mating takes place immediately after emergence. Both mated and unmated females lay eggs, with mated females laying on average 389 eggs each, and unmated females laying about 87 sterile eggs. The egg stage takes on average 2.5 days. Larval development takes 3.6, 3.3 and 3.0 days for the first, second and third instars, respectively, while the pre-pupal and pupal stages take 2.8 and 6.1 days, respectively. Adult females live for 48–78 h, while males live for 24–30 h. The life cycle of O. oryzivora is completed within 21–24 days under screenhouse conditions. The adult male is slender and about 3 mm long, while the female is more rounded with a 4 mm long body and a bright red abdomen. The insect produces unisexual progeny. Field incidence is low at the beginning of the rainy season, peaking with the peak in rainfall and humidity that concurs with the vegetative stage of the crop. The population of the midge declines as temperatures rise. In conclusion, prediction models may be developed based on weather parameters, to aid in forecasting the field incidence of O. oryzivora and its management strategies. Furthermore, it maybe possible to reduce the damage caused by O. oryzivora to rice crops by altering planting period and taking into account environmental factors.

Parasitoid biodiversity conservation for sustainable management of the African rice gall midge, Orseolia oryzivora (Diptera: Cecidomyiidae) in lowland rice

Abstract Platygaster diplosisae and Aprostocetus procerae attack both the African rice gall midge (AfRGM), Orseolia oryzivora, and Orseolia bonzii, a closely related gall midge that feeds on Paspalum scrobiculatum. Recent research has shown that managing this weed at the edge of rice fields offers African farmers, low-cost non-chemical control of AfRGM.

QTL Mapping in Three Rice Populations Uncovers Major Genomic Regions Associated with African Rice Gall Midge Resistance

African rice gall midge (AfRGM) is one of the most destructive pests of irrigated and lowland African ecologies. This study aimed to identify the quantitative trait loci (QTL) associated with AfRGM pest incidence and resistance in three independent bi-parental rice populations (ITA306xBW348-1, ITA306xTOG7106 and ITA306xTOS14519), and to conduct meta QTL (mQTL) analysis to explore whether any genomic regions are conserved across different genetic backgrounds. Composite interval mapping (CIM) conducted on the three populations independently uncovered a total of 28 QTLs associated with pest incidence (12) and pest severity (16). The number of QTLs per population associated with AfRGM resistance varied from three in the ITA306xBW348-1 population to eight in the ITA306xTOG7106 population. Each QTL individually explained 1.3 to 34.1% of the phenotypic variance. The major genomic region for AfRGM resistance had a LOD score and R2 of 60.0 and 34.1% respectively, and mapped at 111 cM on chromosome 4 (qAfrGM4) in the ITA306xTOS14519 population. The meta-analysis reduced the number of QTLs from 28 to 17 mQTLs, each explaining 1.3 to 24.5% of phenotypic variance, and narrowed the confidence intervals by 2.2 cM. There was only one minor effect mQTL on chromosome 1 that was common in the TOS14519 and TOG7106 genetic backgrounds; all other mQTLs were background specific. We are currently fine-mapping and validating the major effect genomic region on chromosome 4 (qAfRGM4). This is the first report in mapping the genomic regions associated with the AfRGM resistance, and will be highly useful for rice breeders.

Morphological diversity and genomic DNA fingerprinting of the African rice gall midge, Orseolia oryzivora (Diptera: Cecidomyiidae) and of two other species of African Orseolia

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.RésuméUne étude de la diversité morphologique a été réalisée sur la cécidomyie de la galle du riz africain, Orseolia oryzivora Harris & Gagné et sur deux autres espèces africaines, O. bonzii Harris et O. nwanzei Harris & Nwilene, sp. n. Les différences morphologiques entre les stades adultes et immatures des trois espèces sont minimes et plus marquées au niveau des caractères nymphaux. A cause des caractères morphologiques limités, la cartographie peptidique de l’ADN génomique de ces trois espèces d’insectes a été effectuée à l’aide de la méthode d’amplification aléatoire d’ADN polymorphe (RAPD) et de la méthode SCAR. Quinze des 90 amorces d’opérons ont montré un polymorphisme chez les trois espèces testées, créant 86 bandes, dont 60 (70%) étaient polymorphes. L’amorce OPV6 a produit trois marqueurs RAPD, qui ont permis de différencier les trois espèces d’Orseoïia. Ces marqueurs ont été clonés et séquencés. Leur séquence a été ensuite utilisée pour concevoir six paires d’amorces SCAR. Les paires des amorces de chaque marqueur SCAR ont permis d’amplifier et de différencier les trois espèces d’Orseolia au niveau de l’ADN génomique. La cartographie peptidique de l’ADN génomique des marqueurs SCAR et RAPD a révélé que les espèces O. oryzivora et O. bonzii sont plus étroitement liées et que O. nwanzei est distincte. Chacune des six paires d’amorces SCAR a produit un segment d’ADN de taille spécifique pour O. nwanzei, O oryzivora et O, bonzii; ces paires d’amorces pourraient donc être utiles pour des diagnostiques de terrain. La cartographie peptidique de l’ADN définie pour chaque espèce d’Orseolia sera utile pour les études entomologiques, l’identification de nouvelles espèces et la différentiation des espèces agressives des espèces non agressives, en vue de développer de façon efficace des cultivars de riz dotés d’une résistance durable à la cécidomyie de la galle du riz africain.

International Trade and Exotic Pests: The Risks for Biodiversity and African Economies

Trade is important for economic development and growth; however, it is also the principal means of introducing invasive pests and disease vectors that can cause environmental damage and economic losses and pose a serious risk to biodiversity. Invasive pests and trade have created a two-way linkage, leading to perceptions that African countries are becoming a source of invasive pests in other countries via trade. What phytosanitary measures do African countries have to take therefore to reduce losses in economic and trade opportunities? Another important issue is the ability of African countries to reduce trade-related pest invasions from other countries and the impact of such invasions on African economies and the environment. Management strategies that can reduce the introduction of exotic pests, while not restricting the benefits of trade or causing protective trade barriers, are desirable. This paper reviews linkages between trade and invasive pests and the resulting effects on African agricultural exports, the economy, environment and biodiversity. Strategies and policies to deal with invasive pests, trade and trade barriers and protectionism are reviewed to assess how they may affect or can be used by African countries to address these problems.

Population dynamics of the African rice gall midge Orseolia oryzivora (Diptera: Cecidomyiidae) and its parasitoids in the forest and southern Guinea savanna zones of Nigeria

The African rice gall midge (AfRGM) Orseolia oryzivora Harris and Gagne is an important insect pest of rice in Nigeria. Studies were conducted at Ogidiga (forest zone) and Edozhigi (southern Guinea savanna) in Nigeria, under rainfed lowland conditions during the 2006 and 2007 rainy seasons, on the population dynamics of AfRGM adults using light trap and random sampling of % tiller infestation (plant damage due to AfRGM) and % parasitism by Platygaster diplosisae Risbec and Aprostocetus procerae Risbec (parasitized larvae and pupae and parasitoid species present in dissected tillers). The results obtained showed that AfRGM populations were relatively low in June and July - the beginning of the 2006 and 2007 rainy seasons, respectively - and increased abruptly from September, reaching a peak in October at both locations. The increase was attributed to the rapid build-up of the pest populations at both locations. There were strong positive correlations between adult populations from light-trap catches and % tiller infestation, and between % tiller infestation and parasitism. The peak period of parasitism by P. diplosisae and A. procerae occurred towards the end of the rainy season in October, coinciding with high level of % tiller infestation. It is concluded that conservation of the parasitoids early in the cropping season (i.e. to improve their synchronization with the host) could become an effective management strategy against AfRGM.

Parasitism and development of Platygaster diplosisae (Hymenoptera: Platygastridae) on the African rice gall midge Orseolia oryzivora (Diptera: Cecidomyiidae).

The life cycle of the koinobiont endoparasitoid Platygaster diplosisae Risbec was investigated to assess its suitability as a biological control agent of the African rice gall midge Orseolia oryzivora Harris & Gagne. Screen house and laboratory experiments were conducted in 2008 under ambient conditions in Ibadan, Nigeria. Morphological characteristics of the parasitoid’s immature stages were observed, and its life cycle parameters were measured. The parasitoid’s average egg incubation period was 12.9 days, and on average, 67.3% of eggs hatched. Three instars occurred, with average developmental durations of 2.2, 0.5 and 2.5 days for the 1st, 2nd and 3rd instars, respectively. Pupal development took 6.7 days until adult emergence. Pre-oviposition period averaged 12.1 h, and a female laid on average 95.2 eggs, with a mean oviposition period of 3.5 days. The longevity of males and females was 3.0 and 4.1 days, respectively, without food; longevity was extended when honey and water were provided. Mating and oviposition behaviours were recorded, and a sex ratio of eight females to one male was found in parasitoid progeny. The parasitoid had a total developmental period of 27.3 days, which is about 5 days longer than that of its host. In conclusion, P. diplosisae can play an important role in the biological control of O. oryzivora on rice, and should be conserved in African rice production systems.

Insect Vectors of Rice Yellow Mottle Virus

Rice yellow mottle virus (RYMV) is the major viral constraint to rice production in Africa. RYMV was first identified in 1966 in Kenya and then later in most African countries where rice is grown. Several studies have been conducted so far on its evolution, pathogenicity, resistance genes, and especially its dissemination by insects. Many of these studies showed that, among RYMV vectors, insects especially leaf-feeders found in rice fields are the major source of virus transmission. Many studies have shown that the virus is vectored by several insect species in a process of a first ingestion of leaf material and subsequent transmission in following feedings. About forty insect species were identified as vectors of RYMV since 1970 up to now. They were essentially the beetles, grasshoppers, and the leafhoppers. For this review, we presented the chronology of their identification. Also, the biology, ecology, host range, distribution, and caused damage of these insects were briefly summarized.

Effect of fungi–termite interaction on the chlorophyll content of three rice varieties grown on ultisol soil of Ikenne, south-west Nigeria

The effect of fungi–termite interaction on three rice varieties was conducted in a screen house at the Africa Rice Center (AfricaRice) Ibadan, Nigeria. Of the 10 fungi species (Fusarium verticilloides, Trichoderma sp., Aspergillus niger, Aspergillus flavus, Macrophoma sp., Neurospora sp., Botryodiplodia theobromae, Penicillum sp., Rhizopus sp. and Sclerotium rolfsii) isolated from termites, soil and rice plants, F. verticilloides, Trichoderma sp. and B. theobromae were used for the interaction study. Each fungus was inoculated singly and in combinations with termite into the root of each rice variety in potted soil. Leaf samples were taken to measure the chlorophyll content which is a major parameter to estimate effect of termite–fungi interaction. The chlorophyll content of the inoculated rice plants was significantly reduced when compared with the control. Fungi interaction with termite had significant reduction on the chlorophyll content. The synergistic relationship between the fungi and the termite was discussed.