Intercropping brassicas with taxonomically unrelated plant species reduced infestations of the aphid Brevicoryne brassicae L. and the rootfly Delia brassicae (Bohé) by over 60% compared with those on brassicas grown in pure stand. Twice as many carabid and staphylinid predators of the immature stages of the rootflies were trapped on intercropped than on brassicas areas, but when they were excluded similar reductions in rootfly eggs occurred suggesting that predation was not an important factor suppressing rootflies in intercrops. Similar numbers of female D. brassicae entered mixed stands indicating that the response of the flies to host‐plant stimuli was not disturbed by non‐host plants. Flies were more active in the laboratory in mixed plantings than in stands of host plants or of non‐ host plants with host‐plant odour blown over them, and their rate of departure from these treatments was correlated with their activity. Oviposition by D. brassicae was reduced in mixed stands. The proximity of host and non‐host plants influenced the diversionary effects of the non‐host plants on oviposition behaviour, so that when 50 cm apart or less, maximum reduction in oviposition occurred. Single row‐intercropping, therefore, appears to be the best arrangement of plants for reducing rootfly attack and was most effective when the intercrop provided at least 50% ground cover between the rows at the time of pest invasion. RÉSUMÉ Effet de l'association culturale sur quelques insectes nuisibles aux choux: réduction des attaques de Brevicoryne brassicae, conséquences pour les entomophages prédateurs épigés, perturbation du comportement de ponte de Delia brassicae L'association des choux avec des plantes sans relations taxonomiques réduit d'environ 60% les attaques de Brevicoryne brassicae et Delia brassicae par rapport aux attaques observées sur cultures pures de choux. Deux fois plus de coléoptères prédateurs des stades larvaires de mouches sont capturés en cultures associées qu'en cultures pures de choux; mais même après élimination des carabidées et staphylinidées, en observe une réduction similaire des effectifs d'ceufs de la mouche de choux, ce qui suggère que la prédation n'est pas un facteur important de régression des populations de D. brassicae en cultures associées. L'entrée d'effectifs comparables de femelles de D. brassicae dans les cultures associées montre que le vol en réponse aux stimuli de la plante‐hôte n'est pas perturbé par les plantes non‐hôtes. Au laboratoire les mouches sont plus actives sur cultures associées ou sur plante non‐hôte mais recevant une odeur de plante‐hôte; leur taux d'envol est dans ces cas proportionnel à leur activité. La ponte de D. bassicae est réduite en cultures associées. La distance entre plantes‐hôtes et non‐hôtes influence l'effet perturbateur des plantes non‐hôtes sur le comportement de ponte, si bien que la réduction la plus efficace est observée pour des distances égales ou inférieures à 50 cm. L'association par rangs alternés paraît être la meilleure disposition pour réduire les...

Lake George is a shallow equatorial lake in Uganda which, around its fringe, has a wetland designated as a Ramsar site of high international importance . A nearby copper mine has caused serious metal pollution of the surrounding land. Results show that heavy metals from mine waste, particularly copper and cobalt, are entering Kahendero Swamp, part of the Ramsar wetland, and contaminating the lake . In the lake, metals pass along the food chain . The distribution of metals in the wetland and possible modes of transport into the lake are discussed . The consequences of the metal contamination are considered and recommendations for its clean-up, especially in the light of future developments, are made .

Variation in temperature affected the developmental periods of eggs, larvae and nymphs of Rhipicephalus appendiculatus Neum. and developmental periods were shortest at an optimum of 30°C. The periods increased as temperatures diverged from the optimum until upper and lower temperature limits were reached, when metabolism ceased. These limits were 16°C and 34°C for eggs, and 12°C and 41°C for larvae and nymphs.Generally, relative humidity did not affect the rate of development. It did, however, critically affect survival, particularly of eggs and larvae. The relative humidity range of 60–70% was critical, and below this range survival of the eggs and larvae was very limited. Nymphs and adults were more resistant, and natural tick populations probably survive hot and dry seasons in these stages.It was found that in a habitat with thick vegetation, temperature and humidity fluctuations were smaller than in one with sparse vegetation, and the former therefore supported a greater tick population. Denying cattle access to this thick vegetation or getting rid of it altogether seem to be possible methods of reducing the tick load of cattle in the area studied.

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A group of 27 variable antigen type (VAT)-specific monoclonal antibodies (McAbs) have been made against metacyclic forms of a cloned stock of Trypanosoma brucei rhodesiense. In combination, these labelled in immunofluorescence 99.3% of trypanosomes in salivary probes from tsetse flies. The 0.7% of unlabelled trypanosomes were believed to be uncoated forms. The ability of a mixture of antibodies to kill metacyclics in vitro by complement-mediated lysis, thus neutralizing their infectivity for mice, was tested. The antibody mixture consisted of 24 McAbs plus 3 VAT-specific rabbit antisera. In 12 replicate experiments this mixture of antibodies prevented infection of mice. Parallel controls showed that neutralization was probably antibody-mediated and VAT specific. However, we have not been able to repeat these results on a long-term basis; this may be due to a loss of neutralizing activity by one of the McAbs. The successful neutralization experiments indicate that the number of VATs in the metacyclic repertoire of one stock of T. b. rhodesiense is limited to at most 27.