Are evergreen mistletoes on deciduous hosts arthropod winter refugia?

Abstract

ABSTRACT Deciduousness is rare among native New Zealand trees, however, non-native deciduous trees now dominate many landscapes. The native evergreen mistletoe Ileostylus micranthus parasitises many non-native deciduous trees, so may be a critically important winter refuge for foliage-dwelling arthropods in deciduous trees. We compared arthropod communities on mistletoes and their evergreen or deciduous hosts in Dunedin, Otago. Foliage samples of 19 hosts and 19 mistletoes parasitising them were collected in summer and winter. Summer samples harboured 1335 arthropods including 1216 mites (Arachnida: Acari), mostly in domatia of two hosts. Winter samples harboured 60 arthropods including 19 mites. Mites were only identified to order but the 160 non-mite arthropods recovered were identified to 26 species or morphospecies in 23 families and 11 orders. The most common non-mite arthropods on hosts were mealybugs (Hemiptera: Pseudococcidae), while bark lice (Psocoptera) were most common on mistletoes. Mistletoes hosted 13 non-mite taxa not found on hosts, which were more likely to be native than those also or only found on hosts. Significantly more non-mite arthropods were found on mistletoes in winter than on their deciduous hosts. There was no difference between mistletoes and evergreen hosts in non-mite arthropod abundance. Mistletoes on deciduous hosts supported higher non-mite arthropod taxonomic richness in winter and over both seasons than their hosts. Despite the small number of non-mite arthropods recovered, our study adds to evidence that mistletoes are important habitat refugia for arboreal arthropods during suboptimal climatic periods, which in our study was during winter on deciduous host trees.