Host ranges and potential as pests: ways of some thrips species in southern areas
R Marullo
Dipartimento di Agrochimica ed Agrobiologia, Universit¨¤ degli Studi Mediterranea di Reggio Calabria, Italy.
Correspondence: rmarullo@unirc.it
Data on the host plant ranges for thrips species are often scanty, and are commonly derived from adult specimens that may have dispersed from their breeding sites. Because of this, there are many difficulties to present a comprehensive list of the host plants for most Thysanoptera species. Despite this, different thrips species exploit the available plants to varying extents, such that some may be considered as monophagous, oligophagous or even polyphagous. Polyphagous thrips species are more likely to be pest species than monophagous or oligophagous species (Moritz G et al. 2004. Pest thrips of the world: an identification and information system using molecular and microscopical methods). Also polyphagous species sometimes produce localized strains with a strong attachment to a particular plant species. Polyphagy and host range might be related to availability of particular compounds in the host plants (Terry I. 1997. In: Thrips as Crop Pests, 65¨C118), or such thrips species might be unusually flexible in their feeding behaviour. However, host plant associations sometimes vary between localities, and a few thrips species are known to exhibit remarkable host shifts (Mound LA. 2005. Annual Reviews of Entomology 50: 247¨C269), such that they become pests on plants unrelated to their ˇ°naturalˇ± hosts. In the present talk two species from southern Italy are considered that have remarkably disjunct host relationships: Neohydatothrips gracilicornis (Williams) on Vicia (Fabaceae) and Pinus (Pinaceae) (Marullo R. 1990. Redia 73 :223¨C228), and Drepanothrips reuteri Uzel on Vitis (Vitaceae) and Quercus (Fagaceae). In contrast the polyphagous species Heliothrips haemorrhoidalis (Bouch¨¨) is expanding as a pest in forest areas, whereas it is no longer a severe pest of Citrus on which crop it is completely supplanted by Pezothrips kellyanus (Bagnall) in the intensive citrus southern orchards (Navel orange, lemon and bergamot). Here, for each thrips species, the main features of the life history, based on field data, and the ˇ°statusˇ± on the new host plants are focused and discussed. N.gracilicornis breeds on plants of wild Vicia spp., and also other Fabaceae, larvae develop mainly in the flowers of these host plants and pupate into the soil. The species is univoltine and overwinters as an adult living in litter or amongst plant debris in the soil. Adults can feed on Pinus needles during autumn and winter, but damage symptoms are induced only on weakly growing plants. Instead, both D.reuteri and H.haemorrhoidalis have Quercus as host plant, on which they breed and can have a few generations per year.
