Identification of ichneumonid wasps using image analysis of wings

Abstract. Image analysis was used to measure the morphological characters of wings of five species of Canadian Itoplectis (Ichneumonidae). The procedure to digitize and measure various elements of the wings with an image analyser is outlined. Specimens were assigned to species by discriminant analysis and independent univariate comparisons of 144 characters from cells, veins and vertices. All the fifty specimens used were assigned to the correct species by both methods. Image analysis of ichneumonid wings is an effective alternative to the conventional identification system.     

Propagation of Date Palm (Phoenix dactylifera L.) in vitro

Adventitious plantlets were obtained from lateral buds, shoottips, embryos, and pieces of stem and rachilla tissue of Phoenixdactylifera L. cultured on a modified Murashige and Skoog mediumcontaining 3 mg l^–1 N-(²-isopenty)adenine 0?1–100mg l^–1 -naphthaleneacetic acid or 2,4-dichlorophenoxyaceticacid, and 3 g l^–1 activated charcoal. Additions of auxinswere necessary to induce explants to produce callus, adventitiousplantlets, and roots. Plantlets were obtained from explantscultured 3–4 months in vitro. No difference in growthresponses between male and female explants was observed duringculture. Complex addenda of activated charcoal and polyvinylpyrrolidonewere tested in the nutrient media at various concentrationsto prevent explant browning. Activated charcoal fostered satisfactorygrowth by reducing the browning and inhibition of growth ofexplants.     

The downstream drifting of larvae of Dixa (Diptera: Dixidae) in two stony streams

SUMMARY. Larvae of Dixa , especially D. puberula Loew., were a significant component of the invertebrate drift in the Walla Brook in southwest England, the Wilfin Beck and the River Duddon in the English Lake District, and the River Estibère in the French Pyrenees. The drifting of the larvae increased markedly at night and showed a definite diel periodicity with maximum numbers usually in the early hours of the night. Seasonal peaks in the density of larvae in the drift frequently occurred in months when adults and especially pupae were present. Most drifting larvae were in the fourth and final instar, and their drift rate usually increased when they were searching for suitable pupation sites.     

Sensitivity to metalaxyl of Phytophthora infestans populations in potato crops in south-west England in 1980 and 1981

A laboratory test was developed to assess the sensitivity of field populations of Phytophthora infestans to metalaxyl. Discs of potato leaf tissue were floated upon solutions of the fungicide at different concentrations and inoculated with spores. The extent of symptom development was noted after incubation under standard conditions for 5–6 days. In preliminary experiments growth of isolates of P. infestans obtained from culture collections was severely inhibited in discs treated at 2 μg/ml. By contrast the development of an isolate obtained from a crop in Eire in which blight control with metalaxyl had failed, and known to be markedly less sensitive in vitro, was unaffected in discs treated at 100 μg/ml. During the summer of 1980, 234 samples of P. infestans were obtained from 20 sites in south-west England, 10 of which had received sprays containing metalaxyl and 10 of which had not. All samples were sensitive to metalaxyl applied at 2 μg/ml. In 1981, 35 sites within the same area, 30 of which had received sprays containing either metalaxyl or ofurace (a related fungicide), were similarly surveyed. Most of the 79 samples of P. infestans examined proved sensitive and at all sites the amount of blight was small. However, at three sites, including one not treated with acylalanine fungicides, strains were found which were unaffected by 100 μg/ml metalaxyl in leaf disc tests. These findings are discussed in relation to the development of resistant blight in other areas and to the use of fungicide mixtures.