Effects of community-wide use of lambdacyhalothrin-impregnated bednets on malaria vectors in rural Sierra Leone

Abstract. The effect of community-wide use of bednets treated with lambdacyhalothrin 10mg/m² on the malaria vector Anopheles gambiae (forest form) was evaluated in Sierra Leone. Sixteen similar villages near the town of Bo were randomly allocated either to remain without nets or to receive treated bednets for all inhabitants, with effect from June 1992. Mosquitoes were sampled using human biting catches on verandas, light-trap catch (beside an occupied untreated bednet), window exit-trap catch and pyrethrum spray collections. During the first year of intervention (June 1992 to July 1993) the treated bednets provided personal protection for people sleeping under them, but had very little impact on densities of An. gambiae collected on human bait. The human blood index (HBI) of An.gambiae was not affected (HBI = 99% in villages with and without nets). An.gambiae parous rates were significantly reduced in all intervention villages, but malaria sporozoite rates fell in only some of the villages. These results are intermediate between those obtained from other projects in Tanzania and Burkina Faso, where treated bednets reduced man-biting, parity and sporozoite rates, versus The Gambia where treated bednets had no significant impact on any of these factors. Possible reasons for these contrasted findings are discussed.     

The Role of Auxin Metabolism in Root Meristem Regeneration by Pinus lambertiana Embryo Cuttings

Since the existence of root promoting substances that consist of a complex between auxin and another molecule has been suggested, we have examined the role of auxin conversion products in root regeneration by Pinus lambertiana embryo cuttings. Auxin conversion products were detected using radioactive forms of the auxins IAA (indoIe-3-acetic acid), NAA (a-napthaleneacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid). 10^?7M NAA was more effective than 10^?6M IAA at promoting rooting, yet it formed conversion products much less rapidly. Also continuous exposure to IAA was necessary for optimum root formation. Based on these and other findings, we conclude that free auxin, and not the conversion products we detected, is essential to root meristem formation.     

A circadian rhythm of locomotor activity in newly emerged Ceratophyllus sciurorum

Abstract Circadian rhythm in newly emerged individuals of the Red Squirrel ( Scuirus vulgaris ) flea C.s. sciurorum was studied in a constant environment, using an insect activity monitor. Trials were run over 7 days using two start times (08.00 and 17.00 hours). The results show that, regardless of start time, the fleas display a 24 h activity rhythm. The presence of a rhythm under constant conditions gives a strong indication that C. s.sciurorum has a self-sustaining clock which is started by disturbance and is most likely to be linked to host activity patterns.     

Observations on the Structure of the Zoospores of Vaucheria

The motile zoospore of Vaucheria has been studied by means ofultraviolet and electron microscopy. The cilia are shown tobe definitely heterokont with an average length difference of1.3 µ between the two members of a pair; they are arrangedin parallel over the spore surface with the shorter cilium ofeach pair orientated towards the front end of the spore. Theinternal structure of the ciliary bases is described from serialsections. The arrangement of the other cell organs throughoutthe spore is discussed in a preliminary way and sufficient structuraldetails are given for identification of mitochondria, fat bodies,nuclei, and plastids. A thin membrane on the spore surface isdemonstrated and a somewhat thicker membrane lining the mainvacuoles is described and its thickness measured. The structureof the cytoplasm is discussed in a preliminary way.     

Observations with the Electron Microscope on Biciliate and Quadriciliate Zoospores in Green Algae

Quadriciliate zoospores of Draparnaldia and biciliate zoosporesof Chaetomorpha have been examined using our previous methods.New features have been seen in both, chiefly in connexion withthe basal organs which attach the cilia to the cytoplasm ofthe parent cell.