Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

To test the hypothesis that pest species diversity enhances biological pest control with generalist predators, we studied the dynamics of three major pest species on greenhouse cucumber: Western flower thrips, Frankliniella occidentalis (Pergande), greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and two-spotted spider mites, Tetranychus urticae Koch in combination with the predator species Amblyseius swirskii Athias-Henriot. When spider mites infested plants prior to predator release, predatory mites were not capable of controlling spider mite populations in the absence of other pest species. A laboratory experiment showed that predators were hindered by the webbing of spider mites. In a greenhouse experiment, spider mite leaf damage was lower in the presence of thrips and predators than in the presence of whiteflies and predators, but damage was lowest in the presence of thrips, whiteflies and predators. Whitefly control was also improved in the presence of thrips. The lower levels of spider mite leaf damage probably resulted from (1) a strong numerical response of the predator (up to 50 times higher densities) when a second and third pest species were present in addition to spider mites, and (2) from A. swirskii attacking mobile spider mite stages outside or near the edges of the spider mite webbing. Interactions of spider mites with thrips and whiteflies might also result in suppression of spider mites. However, when predators were released prior to spider mite infestations in the absence of other pest species, but with pollen as food for the predators, we found increased suppression of spider mites with increased numbers of predators released, confirming the role of predators in spider mite control. Thus, our study provides evidence that diversity of pest species can enhance biological control through increased predator densitie

A temporal escape of one of two pest species from control by Amblyseius swirskii, when a second prey is present

Wanneer twee soorten plaaginsecten aanwezig zijn in de kas, kan één van beide soorten ontsnappen aan de predator die als biologische bestrijding is uitgezet. Dit is aangetoond in een proef met Amblyseius swirskii. Na enkele weken werd het effect tenietgedaan door de toename van het aantal predatoren

Intended signals and ambient electromagnetic noise in HF spectrum management

Both spectrum management – the organization of radio services in the spectrum to maximize spectrum utility – and radio link planning and the associated equipment design require a-priory knowledge of the electromagnetic environment. The dynamic range of the planned radio system must be able to support the accumulated power of intended radio signals within the bandwidth of the receiver front-end, and the ambient electromagnetic noise field strength must be accounted for in the link budget calculations. These items are especially important for sensitive receivers in the HF (3-30 MHz) frequency range, e.g. for radio astronomy or emergency communications. This paper will discuss these spectrum management and equipment design issues, with an emphasis on ambient electromagnetic noise