Developmental biology and field performance of Platygaster diplosisae Risbec (Hymn: Platygasteridae) an egg-larval parasitoid of african rice gall midge Orseolia oryzivora Harris and Gagné (Diptera: Cecidoymiidae)

The developmental biology and field performance of Platygaster diplosisae an endoparasitoid of African rice gall midge (AfRGM) Orseolia oryzivora were investigated. Experiments were conducted in the screen house, laboratory and fields during 2006/2007 farming seasons. The pre-oviposition period averaged 12.1 h. The mean number of eggs laid per female was 95.2 and mean oviposition period was 3.5 days. The average incubation period was 13.0 days with a hatchability of 67.3%. There were three larval instars with developmental duration averaging 2.2, 0.5 and 2.5 days for the 1st, 2nd and 3rd larval respectively. The prepupa and pupa developmental period lasted for 2.4 and 6.7 days respectively. The longevity of males and females were 3.0 and 4.1 days respectively without food, which varied when food was given. The parasitoid has total developmental period of 27.3 days. The results showed that P. diplosisae has an impact as a bio-control agent of AfRGM, but the percentage parasitism of the host was low at the beginning of the season and increased significantly later in the season with a peak in October of each season. It was recommended that mass rearing or conservation of the parasitoid be adopted to improve its efficiency in control of AfRGM.Keywords: Biology, Platygaster diplosisae, bio-control, field impact, Orseolia oryzivora

Effects of biofertilizer containing N-fixer, P and K solubilizers and AM fungi on maize growth: A greenhouse trial.

An in vitro study was undertaken to evaluate the compatibility of indigenous plant growth promoting rhizobacteria (PGPR) with commonly used inorganic and organic sources of fertilizers in tea plantations. The nitrogenous, phosphatic and potash fertilizers used for this study were urea, rock phosphate and muriate of potash, respectively. The organic sources of fertilizers neem cake, composted coir pith and vermicompost were also used. PGPRs such as nitrogen fixer; Azospirillum lipoferum, Phosphate Solubilizing Bacteria (PSB); Pseudomonas putida, Potassium Solubilizing Bacteria (KSB); Burkholderia cepacia and Pseudomonas putida were used for compatibility study. Results were indicated that PGPRs preferred the coir pith and they proved their higher colony establishment in the formulation except Azospirillum spp. that preferred vermicompost for their establishment. The optimum dose of neem cake powder

Effect of Neem Seed Kernel Extracts in the Management of Rice Stem Borers in the Field in Nigeria

Stem borers are economic pests of rice and its management through conventional methods has not given the desired results. Hence in this study field experiments were conducted to determine the comparative efficacy of neem seed kernel extracts (Azadirachta indica; (Neem) and synthetic insecticide (Carbofuradan) against rice stem borers in Nigeria during 2006/07 farming season. The effect of these sprayings was also recorded on natural enemies and yield attributes. Results showed that the two pesticides significantly (p < 0.01) reduced stem borers damage (number of dead hearts, white heads) compared to untreated check, and also significantly (p < 0.05) increased number of productive tillers with resultant increase in grain yield than the control plots. Maximum numbers of different natural enemies were found in neem extract treated plots against the carbofuran treated plots. It is suggested that on the basis of infestation of borer, high yield and conservation of natural enemies, neem seed extract can be regarded as suitable alternative to synthetic insecticides for the management of rice stem borers in the field.Keywords: Botanical/insecticide, stem borer controlNig J. Biotech. Vol. 23 (2011) 13- 2

Identification and differentiation of three Nigerian Orseolia sp. by RAPD markers

Identification and differentiation of three Nigerian Orseolia sp. (Orseolia nwanzei, Orseolia bonzii and Orseolia oryzivora) was carried out using Random Amplified Polymorphic DNA (RAPD) markers. Ninety operon primers were screened, from which 6 showed polymorphism among the three species tested, generating 54 bands, 69% of which were polymorphic with sizes ranging between 1000 and 3000 bp. DNA fingerprints of adults and pupae of each species were genetically identical. O. oryzivora and O. bonzii are identified as most closely related, while O. nwanzei is distinct. The DNA fingerprints identified for each Orseolia sp. will be useful for entomological survey for the identification of new species within the context of the effective development of rice cultivars with durable resistance to AfRGM

Electrophysiological and behavioral responses of female African rice gall midge, Orseolia oryzivora Harris and Gagné, to host plant volatiles.

African rice gall midge, Orseolia oryzivora Harris and Gagné, is a major pest of rice in Africa. Depsite its economic importance, its chemical ecology is not well understood. Here, we assessed behavioral and electrophysiological responses of O. oryzivora to host plant volatiles. In olfactometer bioassays, mated female O. oryzivora were attracted to volatiles emitted from intact rice plants but were repelled by volatiles collected from plants infested by conspecifics. In a choice test, there was a preference for volatiles from uninfested plants over those from infested plants. Coupled gas chromatography-electroantennography analyses of panicle volatiles isolated four electrophysiologically active components: (S)-linalool, 4,8-dimethyl-1,3,7-nonatriene, (E)-caryophyllene, and (R/S)-(E)-nerolidol. A synthetic blend of volatiles at the same concentration and ratio as that from an intact plant was attractive to mated females, whereas a blend based on the ratio of volatiles from an infested plant was repellent. This suggests that O. oryzivora uses olfaction for host plant recognition. The identification of blends of volatiles emitted by plants that can both attract and repel O. oryzivora may aid the development of sustainable control measures

Identification and differentiation of Orseolia species in Nigeria as revealed by SCAR-PCR analysis

Identification and differentiation of Orseolia species in Nigeria was carried out using SCAR-PCR analysis. Twenty-three insects from 9 localities in Nigeria and three reference insects (Orseolia bonzii, Orseolia nwanzei and Orseolia oryzivora) were analyzed. Out of the 60 SCAR primers screened, only four produced clear amplified DNA fragments at annealing temperature of 55°C that differentiated all the 26 Orseolia species. Cluster analysis revealed two major insect genotypes (OSG-1 and OSG-2). The OSG-1 was further divided into two subgroups (OSG-1a and OSG-1b). Eleven insects were genotyped as OSG-1a, 14 as OSG-1b and one as OSG-2. Only NG1 and NG2 were identical among the insects of OSG-1a genotype. OSG-1b genotype produced two different groups of identical insects. While O. bonzii and O. oryzivora were genotyped as OSG-1b along with other twelve insects, only O. nwanzei was genotyped as OSG-2. OSG-1b genotype constitutes about 54% O. bonzii and O. oryzivora in Nigeria, OSG-2 genotype represents 4% of O. nwanzei in Nigeria while OSG-1a genotype covers 42% of yet unknown Orseolia species in Nigeria. This information would strongly assist breeding programmes aiming at effective development of cultivars with durable resistance to African rice gall midge (AfRGM) in Nigeria