Number, Seasonality and Feeding Habits of Insects Attacking Ferns in Britain: An Ecological Consideration

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Abstract
Six fern species (Dryopteris filix-mas, D. borreri, D. dilatata, Polypodium vulgare, Phyllitis scolopendrium and Polystichum setiferum) were sampled for phytophagous insects in a range of habitats in southwestern England [UK]. The field data, supported by a survey of the literature, suggest that there are fewer phytophagous insect species associated with these ferns than with other equally common vascular plants. Evidence is presented that this is a consequence of the wide range of chemical defenses found in ferns. The young fern fronds have a high potential nutritive value for phytophagous insects but high concentrations of defense compounds are also present which may protect the fronds from attack. Highest numbers of insect species and individuals are found in late summer when not only the levels of defense compounds but also the nutritional value of mature fronds is low. The major insect orders associated with British ferns (comprised of 63 spp. of which 46 spp. are monophagous) are Hemiptera, Hymenoptera, Diptera and Lepidoptera; the Coleoptera are poorly represented. These groups exhibit life histories and feeding habits (63% of the species are highly selective in their feeding sites) which can be interpreted in terms of spatio-temporal adaptations to the biochemistry of ferns.