Potential impact of insect herbivores on orchid conservation

Abstract

When an orchid is deliberately or inadvertently relocated, it is likely to encounter a range of biological challenges to long term survival including a complex and dynamic insect community which could alter conservation expectations yet there have been few studies of the phytophagous insects associated with wild orchids. We have investigated the assemblage of such insects associated with terrestrial orchids being monitored in our long term studies in Gatineau Park, Québec, Canada. Aphids, leafminers, moths, thrips, weevils, and whiteflies were found to be injurious to orchids although in different combinations and with varying impact according to the orchid host, habitat and year. Loss of seeds and even complete desiccation of plants was observed. Where the leafminer, Parallelomma vittatum Meigen (Diptera: Scathophagidae) infested Cypripedium reginae Walter randomly, this was not the case with Cypripedium parviflorum var. pubescens (Willd.) Knight where specific plants were repeatedly infested. Some infestations such as with the leafminers seemed to be in equilibrium with parasitoids thus minimizing potential impact. A likely climate-related asynchrony of parasitoid and leafminer led to an outbreak in 2009 which heavily impacted the introduced Epipactis helleborine (L.) Crantz while a phenological shift in a thrips primary host, Trillium grandiflorum (Michaux) Salisb. (Melanthiaceae), in 2010, contributed to severe herbivory in habitats where both E. helleborine and trillium occurred. If climate change can lead to changes in insect abundance and impact on orchids, it would be useful to investigate the potential impact of phytophagous insects before assisted migration is considered as a conservation measure.