Do characteristics of pollinator-friendly gardens predict the diversity, abundance, and reproduction of butterflies?

Published source details Majewska A.A., Sims S., Wenger S.J., Davis A.K. & Altizer S. (2018) Do characteristics of pollinator-friendly gardens predict the diversity, abundance, and reproduction of butterflies?. Insect Conservation and Diversity, 11, 370-382.
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This study is summarised as evidence for the following.

	Action	Category
	Practise ‘wildlife gardening’ Action Link
	Remove, control or exclude native predators Action Link
	Plant parks, gardens and road verges with appropriate native species Action Link

Practise ‘wildlife gardening’

A replicated, paired, controlled study in 2013–2014 in a managed park in Georgia, USA (Majewska et al. 2018) found that areas with reduced weeding had a similar overall abundance and species richness of adult butterflies, and adults, eggs and caterpillars of four target species, compared to areas with regular weeding. The total abundance and species richness of butterflies was similar in plots weeded every two months and plots weeded every two weeks (data presented as model results). In addition, the abundance of adults, eggs and caterpillars of four target species (monarch Danaus plexippus, queen Danaus gilippus, gulf fritillary Agraulis vanillae, and black swallowtail Papilio polyxenes) were similar in plots with reduced weeding and plots with regular weeding (see paper for details). In spring 2013, four fenced, irrigated experimental plots (7.6 × 15.2 m, 20–88 m apart) were established in each of three blocks, 250 m apart. Each plot was planted with 128 plants of 13 species, and was surrounded by mown grass. Plots were assigned to four treatments/block: planting with native or non-native species, and low (every other month) or high (every other week) weed maintenance by hand pulling, trimming, and spot herbicide application. From May–September 2014, adult butterflies were surveyed for 7 minutes/plot, 1–4 times/month, and eggs and caterpillars of four species (monarch, queen, black swallowtail, gulf fritillary) were counted weekly or monthly on 2–14 host plants/butterfly species/plot.

(Summarised by: Andrew Bladon)
Remove, control or exclude native predators

A replicated, paired, controlled study in 2014 in a managed park in Georgia, USA (Majewska et al. 2018) found that excluding terrestrial predators did not increase the survival of monarch Danaus plexippus caterpillars. The survival of monarch caterpillars from first to fifth instar was similar on plants where terrestrial predators were excluded and on plants without predator exclusion (data presented as model results). Swamp milkweed Asclepias incarnata plants were grown in greenhouses, and placed outside in July 2014. Plants were paired at 28 locations, six within grassland plots planted with native species, six within grassland plots planted with exotic species, and 16 in open grassland and forest edges. One plant/pair was placed in a 2-litre tub of water with Tanglefoot^TM applied to the rim of the pot to exclude non-flying predators (mainly ants) and the other was placed directly on the ground. Each plant was surrounded by fencing to prevent deer browsing. In October 2013, monarch butterflies were collected on migration, and reared for two generations. In July 2014, two to four first-instar caterpillars were placed on each milkweed and monitored daily until they reached the fifth instar.

(Summarised by: Andrew Bladon)
Plant parks, gardens and road verges with appropriate native species

A replicated, paired, controlled study in 2013–2014 in a managed park in Georgia, USA (Majewska et al. 2018) found that areas planted with native flowers had a similar overall abundance and species richness of adult butterflies, but fewer adults and/or eggs, and more caterpillars, of specific species than areas planted with non-native flowers. The total abundance and species richness of butterflies was similar in plots planted with native and non-native plants (data presented as model results). However, in native flower plots the abundance of monarch Danaus plexippus (0.1–0.2 butterflies/plot) and gulf fritillary Agraulis vanillae adults (0.3–0.5 butterflies/plot), and of monarch and queen Danaus gilippus eggs (0.1 eggs/plant) was lower than in non-native flower plots (monarch: 1.6–3.1 butterflies/plot; gulf fritillary: 1.3–1.4 butterflies/plot; eggs: 0.7 eggs/plant). The abundance of black swallowtail Papilio polyxenes caterpillars was higher in native plots (0.7 caterpillars/plant) than in non-native plots (0.6 caterpillars/plant). Authors suggested that the difference in the number of butterflies of some species may have been caused by the fact that there were fewer flowering plants in native than non-native plots. In spring 2013, four fenced, irrigated experimental plots (7.6 × 15.2 m, 20–88 m apart) were established in each of three blocks, 250 m apart. Each plot was planted with 128 plants of 13 species, and was surrounded by mown grass. Plots were assigned to four treatments/block: planting with species native to Georgia or not native to the USA, and low (every other month) or high (every other week) weed maintenance. From May–September 2014, adult butterflies were surveyed for 7 minutes/plot, 1–4 times/month, and eggs and caterpillars of the four species were counted weekly or monthly on 2–14 host plants/butterfly species/plot.

(Summarised by: Andrew Bladon)