This study describes a new baculovirus isolate recovered from infected larvae of the diamondback moth, Plutella xylostella (L.), and identified as a multiple nucleopolyhedrovirus (MNPV). The plaque purified isolate designated as PxMNPVCL3 was found to be pathogenic to P. xylostella, Heliothis virescens (F.), Trichoplusia ni (Hübner), H. subflexa (Guenée), Helicoverpa zea (Boddie), Spodoptera exigua (Hübner), and S. frugiperda (J. E. Smith) larvae in decreasing order of susceptibility. The LC50 for diamondback moth, the most susceptible, was 6 occlusion bodies (OB)/cm2, whereas the most resistant species, namely S. frugiperda, was 577 OB/cm2. PxMNPVCL3 was more pathogenic to diamondback moth by 3-4 log cycles as compared with 2 broad-spectrum baculoviruses, namely Autographa california (alfalfa looper) MNPV and Anagrapha falcifera (celery looper) MNPV. The 3 baculoviruses were compared with each other and characterized by restriction endonuclease (REN) analysis, hybridization, and neutralization tests. Fragmentation profiles generated by REN showed that the 3 baculoviruses shared some fragments in common. Hybridization studies employing digoxigenin labeled PxMNPVCL3 DNA as a probe revealed the close but distinct relationship of these 3 viruses. Neutralization tests confirmed the hybridization studies, namely that the 3 viruses although genetically similar are distinguishable from each other.

Diadegma semiclausum (Hellén) (Hymenoptera: lchneumonidae), an exotic diamondback moth parasitoid, was released in two pilot areas (Werugha in Coast Region and Tharuni in Central Province) in Kenya. Fifteen month before release, observations on the diamondback moth, Plutella xylostella (Linnaeus), and local natural enemy population dynamics and pest damage were initiated in both areas and continued for three years after release. The P. xylostella population was bimodal with higher records during dry seasons. At Werugha, the peak population of P. xylostella was 16.8 per plant (October 2001); at Tharuni it was 12.8 (February 2002). Populations at Werugha declined from three months after release and decreased from 5.4 per plant (before release) to 0.8 (year 3 after release). Concurrently, average damage (1.9 to 1.5) (on a 0-5 scale), proportion of attacked plants (72 to 31%) and proportion of plants in damage group >2 (plants with head damage) decreased (21.4 to 5.3%), while total parasitism increased from 14.4 (before) to 52.5% (year 3 after release, 90% due to D. semiclausum). At Tharuni, D. semiclausum was only recovered 3 months after release. Average populations of P. xylostella declined from 5.9 per plant (before release) to 2.4 (year 3 after release) and damage scores from 2.3 to 1.7. The proportion of plants in damage group >2 declined from 39.7 to 4.5% while overall parasitism increased from 4.2 to 40.6% (98.3% by D. semiclausum). Four species of indigenous parasitoids (Diadegma mollipla (Holmgren), Oomyzus sokolowskii (Kurdjumov), Apanteles sp. and Itoplectis sp., all primary parasitoids) were almost completely displaced by D. semiclausum. Possible reasons for the different parasitoid development between the two release areas and the displacement of the indigenous species are discussed.

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Yield-phenology relation is a critical issue affecting rainfed maize field productivity in semiarid east African Plateau (EAP). We first introduced Chinese ridge-furrow mulching (RFM) system to EAP, using three maize cultivars with early-, mid- and late-maturing traits as test materials. A two-year field experiment was conducted in a semiarid farm of Kenya from 2012 to 2013. Three treatments were designed: alternative ridge and furrow with transparent plastic mulching (FT), with black plastic mulching (FB) and without mulching (CK). We found that FT and FB significantly increased soil moisture and accelerated crop maturity across two growing seasons. Leaf area and shoot biomass were increased by 30.2% and 67.5% in FT, 35.2% and 73.5% in FB, respectively, compared with CK. Grain yield, water use efficiency and economic output were increased by 55.6%, 57.5% and 26.7% in FT, and 50.8%, 53.3% and 19.8% in FB, respectively. Optimal yield and economic benefit were observed in late-maturing cultivar due to increased topsoil temperature in FT in 2012 (cool), and in early-maturing cultivar owing to cooling effect in FB in 2013 (warm). Our study suggested RFM system, combined with crop phenology selection, be a promising strategy to boost maize productivity and profitability in semiarid EAP.

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