Beauty with benefits: butterfly conservation in Washington State, USA, wine grape vineyards

Abstract

The butterfly fauna of south central Washington State, USA is characterized by shrub-steppe specialists adapted to hot, dry summers and cold winters. However, the shrub-steppe ecosystem has diminished at an alarming rate due to extensive agricultural development fostered by access to an abundant water supply from the Cascade Mountains. This has resulted in loss and fragmentation of habitat for ~50 species of butterflies which are now in decline. Viticulture is a major agricultural industry in south central Washington and has transitioned in recent years to a sustainable, low pesticide-input enterprise. Current viticultural pest management research is focused on restoration of shrub-steppe habitat and native plants to enhance and sustain beneficial arthropod populations (predators and parasitoids) for pest control. Butterfly populations were surveyed during 2012–13 in a pair of vineyards (habitat-enhanced, conventional) in each of four viticultural regions [Columbia gorge (CG), Walla Walla valley (WWV), Yakima valley (YV), Wahluke slope (WS)] in south-central Washington. The habitat-enhanced sites supported a significantly greater number of flowering plant species (mostly native) than conventional vineyard sites. Twenty nine butterfly species were recorded from the habitat-enhanced vineyards with only nine of these recorded from the conventional vineyards. Overall, there were double the number of species in habitat-enhanced vineyards [mean (±SE) 5.62 ± 0.85] compared to conventional vineyards (2.75 ± 0.75) although this was not statistically significant. A significantly greater number of species occurred in the CG and WWV habitat-enhanced vineyards (10.5 ± 0.5) compared to the conventional vineyards (3.5 ± 0.0) in these regions. Smaller numbers of butterfly species occurred in YV and WS vineyards with no significant differences between habitat-enhanced and conventional sites. Butterfly abundance was significantly greater in habitat-enhanced vineyards (20.37 ± 5.34 individuals/visit) compared to conventional vineyards (5.5 ± 0.9) with greatest differences in the CG and WWV vineyards. The pest management strategy of restoring native plants and habitats in a low pesticide-input crop like wine grapes in central Washington may have substantial benefits for butterfly abundance, diversity and conservation. Many of the flowering native perennials important in attracting and sustaining endemic biological control agents, are also larval hosts and/or nectar sources for threatened shrub-steppe butterflies.