International Institute of Tropical Agriculture

About: International Institute of Tropical Agriculture is a nonprofit organization based out in Ibadan, Nigeria. It is known for research contribution in the topics: Population & Agriculture. The organization has 2638 authors who have published 4330 publications receiving 119041 citations. The organization is also known as: IITA.

Evidence of a multiple insecticide resistance in the malaria vector Anopheles funestus in South West Nigeria

Abstract: Knowing the extent and spread of insecticide resistance in malaria vectors is vital to successfully manage insecticide resistance in Africa. This information in the main malaria vector, Anopheles funestus sensu stricto, is completely lacking in the most populous country in Africa, Nigeria. This study reports the insecticide susceptibility status and the molecular basis of resistance of An. funestus as well as its involvement in malaria transmission in Akaka-Remo, a farm settlement village in southwest Nigeria. Plasmodium infection analysis using TaqMan protocol coupled with a nested PCR revealed an infection rate of 8% in An. funestus s.s. from Akaka-Remo. WHO susceptibility tests showed this species has developed multiple resistance to insecticides in the study area. Anopheles funestus s.s. population in Akaka-Remo is highly resistant to organochlorines: dieldrin (8%) and DDT (10%). Resistance was also observed against pyrethroids: permethrin (68%) and deltamethrin (87%), and the carbamate bendiocarb (84%). Mortality rate with DDT slightly increased (from 10 to 30%, n = 45) after PBO pre-exposure indicating that cytochrome P450s play little role in DDT resistance while high mortalities were recorded after PBO pre-exposure with permethrin (from 68 to 100%, n = 70) and dieldrin (from 8 to 100%, n = 48) suggesting the implication of P450s in the observed permethrin and dieldrin resistance. High frequencies of resistant allele, 119F in F0 (77%) and F1 (80% in resistant and 72% in susceptible) populations with an odd ratio of 1.56 (P = 0.1859) show that L119F-GSTe2 mutation is almost fixed in the population. Genotyping of the A296S-RDL mutation in both F0 and F1 samples shows an association with dieldrin resistance with an odd ratio of 81 (P < 0.0001) (allelic frequency (R) = 76% for F0; for F1, 90 and 10% were observed in resistant and susceptible populations, respectively) as this mutation is not yet fixed in the population. The study reports multiple insecticide resistance in An. funestus from Akaka Remo. It is, therefore, necessary to pay more attention to this major malaria vector for effective malaria control in Nigeria.

Effect of plant lectins on larval development of the legume pod borer, Maruca vitrata

Abstract: The legume pod-borer Maruca vitrata (Fabricius), [Lepidoptera: Pyralidae] is a major constraint restricting increased cowpea production in tropical Africa and Asia. Since lectins are known to have insecticidal properties against several pests, a survey was undertaken to screen for the effects of 25 lectins from 15 plant families on the development of Maruca pod borer (MPB) larvae. The list included 8 galactose/N-acetylgalactosamine-, 7 mannose-, 5 complex glycan-, 2 sialic acid- and 3, N-acetylglucosamine-specific lectins. Feeding bioassays using artificial diet were carried out at 2% (w/w) topical levels. Although a total of 16 lectins had detrimental effects pertaining either to larval survival, weight, feeding inhibition, pupation, adult emergence and/or fecundity, only the Listera ovata agglutinin (LOA) (Orchidaceae) and Galanthus nivalis (Amaryllidaceae) agglutinin were effective against MPB larvae for all six parameters examined. Larval mortality and feeding inhibition caused by the most active lectin (LOA) was above 60%.

Evaluation of Soybean Germplasm for Resistance to Soybean Rust (Phakopsora pachyrhizi) in Nigeria.

Abstract: Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important constraints to soybean production worldwide. The absence of high levels of host resistance to the pathogen has necessitated the continued search and identification of sources of resistance. In one set of experiments, 178 soybean breeding lines from the International Institute of Tropical Agriculture were rated for rust severity in the field in 2002 and 2003 at Ile-Ife, Yandev, and Ibadan, Nigeria. Thirty-six lines with disease severity ≤3 (based on a 0-to-5 scale) were selected for a second round of evaluation in 2004 at Ibadan. In the third round of evaluation under inoculated field conditions, 11 breeding lines with disease severity ≤2 were further evaluated for rust resistance at Ibadan in 2005 and 2006. The breeding lines TGx 1835-10E, TGx 1895-50F, and TGx 1903-3F consistently had the lowest level of disease severity across years and locations. In another set of experiments, 101 accessions from the United States Department of Agriculture-Agricultural Research Service and National Agriculture Research Organization (Uganda) were evaluated in the first round in 2005 under inoculated conditions in the screenhouse; 12 accessions with disease severity ≤20% leaf area infected were selected for evaluation in the second round in 2005 and 2006 under inoculated field conditions at Ibadan. Highly significant differences (P < 0.0001) in disease severity were observed among the 101 accessions during this first round of rust evaluation. Significant (P < 0.0001) differences in rust severity and sporulation also were observed among the 12 selected accessions. Accessions PI 594538A, PI 417089A, and UG-5 had significantly (P < 0.05) lower disease severity than all other selected accessions in both years of evaluation, with rust severities ranging from 0.1 to 2.4%. These results indicate that some of the breeding lines (TGx 1835-10E, TGx 1895-50F, and TGx 1903-3F) and accessions (PI 594538A, PI 417089A, and UG-5) would be useful sources of soybean rust resistance genes for incorporation into high-yielding and adapted cultivars.

Plant diversity management in cocoa agroforestry systems in West and Central Africa—effects of markets and household needs

Abstract: Cocoa production in humid forest landscapes has been one of the main cash providers of West and Central African economies. Along with the liberalization of the perennial tree sector, there are increased fluctuations of cocoa income. At the same time, the demand and interest for timber production and non-wood forest products have also been increasing. With the continuous disappearance of natural forests, the production of these commodities is being shifted into cocoa agroforests and plantations. In view of helping research and development institutions in promoting sustainable tree crop systems, this paper attempts, for the main cocoa producing countries of West Africa (Cameroon, Nigeria, Ghana and Cote d’Ivoire), to: (1) document the temporal evolution of the market demand for forests and non-wood forest products both at the local and international levels; (2) explore the set of tree species that can be produced in cocoa agroforests of WCA to satisfy this demand. Deforestation resulting partly from the expansion of perennial orchards and slash and burn agriculture is: (i) leading to a shortage of suitable forest land necessary to stabilize or increase national cocoa production and (ii) increasing the gap between the demand and availability/supply of non-wood forest products (NWFP) and timber by reducing the main source of these products—the forest. Demand of these products is increasing with the growth of urban and peri-urban centers. At the same time, perennial agroforestry systems such as cocoa agroforest are increasingly perceived as assets for Payment for Environmental Services (PES) such as carbon storage and biodiversity conservation, because of the potential of the resources that they can generate. These demands of products and payment for ecosystem services that can be provided by sustainable cocoa agroforestry systems depends upon the appropriate combination of cocoa, timber and non-timber forest trees on the same land. Such demands is still to be properly exploited in the region. Cocoa agroforests in West Africa are characterized by fewer species than those of Central Africa. The level of market access influences the types of species that are managed inside cocoa agroforests. Among the species potentially associable with cocoa, those demanded by the local, regional and international markets are not necessarily the ones that are more frequent in the cocoa fields. The gradual reduction of natural forest, from which timber and non-timber products are gathered, aroused the need to integrate the growing of such species in cocoa agroforestry systems.

Assessment of key factors responsible for the pest status of the bean flower thrips Megalurothrips sjostedti (Thysanoptera: Thripidae) in West Africa

Abstract: Megalurothrips sjostedti (Trybom) is an important pest of cowpea (Vigna unguiculata) in West Africa. Three key factors assumed to be responsible for its pest status are analysed, the survival on alternative host-plants during the dry season, the inefficient biotic mortality factors regulating population growth, and the effect of larval feeding on the development of cowpea flower buds. Extensive surveys indicate clearly that M. sjostedti survives the dry season on a wide range of alternative hosts all belonging to the Leguminosae, where it can feed and reproduce. Different antagonists were observed attacking eggs and larvae of M. sjostedti; their impact, however, is low and cannot prevent pest outbreaks. Two undescribed Megaphragma spp., and one Oligosita sp., all trichogrammatid egg parasitoids, were recorded for the first time. The anthocorid Orius sp. was the most important larval predator. No hymenopterous parasitoids could be reared from larvae collected on cowpea and three major alternative hosts, whereas a low percentage of the larvae collected from the flowers of Tephrosia candida, an exotic shrub native to India, were parasitized by the eulophid Ceranisus menes (Walker), also recorded for the first time in Africa. The feeding activity of six larvae of Megalurothrips sjostedti during five days induced the shedding of all flower buds of a cowpea inflorescence. The results of the analysis shed new light on the M. sjostedti pest problem, and the ways to solve it. The lack of efficient antagonists, particularly larval parasitoids known from closely related south-east Asian Megalurothrips spp., and the high damage threshold, indicate that M. sjostedti is a potential target for biological control. However, further studies are needed to investigate the migration of M. sjostedti adults to and from alternative host-plants, in order to reinforce the action of biocontrol with cultural pratices.