Population dynamics of mites in slow-release sachets used in biological control: a new study methodology

Predatory mite species (Acari: Phytoseiidae) are essential tools in the biological control of greenhouses pests. The natural enemies can be released directly into a crop. A better, partly preventive system is to place slow-release sachets on the plants. Inside such sachets is a factitious prey's food substrate-which also acts as refuge-and the predator. The objective of this study was to develop a new methodology to evaluate the population dynamics of this sachet system, based on the factitious prey Carpoglyphus lactis and the predatory mite Amblyseius swirskii. Through two tests carried out under laboratory conditions, the sachets were first compared to the traditional extraction method that uses Berlese-Tullgren funnels and an extraction method using flotation in hexane. The latter method proved more effective at sampling the motile states (larvae, nymphs, and adults), both for the predatory species and for the factitious prey, extracting up to 3.7 × more mites than the Berlese-Tullgren funnel. Second, the population dynamics of both mite species was studied in a laboratory test, both inside and outside the sachets. In this way, a positive correlation was demonstrated between the number of predatory mites and the number of prey mites inside the sachets. Conversely, no correlation was found between the interior population of predatory mites and the number that venture outside. We can conclude that hexane extraction is very useful both in quality control of predatory mites and in studying how the sachets behave when faced with various factors.

Attraction of male turnip mothsAgrotis segetum (Lepidoptera: Noctuidae) to sex pheromone components and their mixtures at 11 sites in Europe, Asia, and Africa

Selected combinations of (Z)-5-decenyl, (Z)-7-dodecenyl, and (Z)-9-tetradecenyl acetates, the pheromone components of the turnip mothAgrotis Segetum were tested for field attractancy at six, two, and three sites in Europe, Asia, and Africa, respectively. At all of the sites in Eurasia and in northern Africa the ternary mixture of the acetates captured most males, while at the sites south of the Sahara in Africa, (Z)-5-decenyl acetate alone was responsible for attraction. Differences in male attraction among the populations studied confirm the existence of significant population variation in the pheromone ofA. segetum. Interpretation of the present results together with earlier studies suggests that this variation is more or less continuous in Eurasia and north Africa, while a clearly distinct pheromone type is present in the areas south of the Sahara desert.

Digestive proteases during development of larvae of red palm weevil, Rhynchophorus ferrugineus (Olivier, 1790) (Coleoptera: Curculionidae)

The evolution of digestive proteases during larval development of Rhynchophorus ferrugineus (Olivier, 1790) has been studied. A progressive increase of protease activity has been found. The optimum pH for proteolytic activity against azocasein was determined. Caseinograms revealed an active complex of alkaline proteases from the early stages of the development. From the apparent molecular masses, three groups of proteases have been found - high molecular-mass proteases, medium molecular-mass proteases, and low molecular-mass proteases. Studies using specific protease inhibitors showed the major presence of serine proteases in gut extracts. The results obtained from larvae reared on different substrates have made possible a comparative assessment of the influence of diet on the development of the digestive enzymatic system. Larvae fed on an artificial diet showed a complete pattern of digestive proteases. Data suggest that this diet seems to be suitable for future research with this insect pest.