High invasive ant activity drives predation of a native butterfly larva

Abstract

Yellow crazy ants (Anoplolepis gracilipes) threaten invertebrates on many tropical islands, but little work has been done in continental ecosystems. We found 4.4-16.0 times more cruiser butterfly caterpillars were attacked in Australian rain forest sites with A. gracilipes than in native ant sites, and extrafloral nectar had little influence. , which may be more susceptible to effects of invasive species than continental ecosystems (Simberloff 1995). Only one published study has investigated effects of A. gracilipes on invertebrate communities on mainlands, and it found no significant effect of A. gracilipes on the abundance or richness of ground invertebrates (Hoffmann & Saul 2010).Butterflies are a group of invertebrates that may be particularly susceptible to invasions by A. gracilipes because their larval stages forage on plants. Larvae that forage on plants with EFN may be particularly at risk because A. gracilipes increases recruitment and aggressive behavior with increasing EFN availability (Savage & Whitney 2011). The aim of our study was to compare attack rates of a native caterpillar by the invasive A. gracilipes and native O. smaragdina. We conducted our experiments on two species of host plants and manipulated access to EFN on one of them. We addressed two questions: (1) are attack rates of caterpillars by A. gracilipes higher than by O. smaragdina? And (2) how does availability of EFN influence attack rates by the invasive and native ant species?We conducted our study with the native cruiser butterfly, Vindula arsinoe (Nymphalidae), an excellent proxy for many threatened butterfly species in the Wet Tropics. It oviposits in clusters, its instars have spines, and it does not sequester phytotoxins. Its preference for lowland rain forest and vine thickets (Braby 2009) overlaps with habitat invaded by A. gracilipes. Vindula arsinoe oviposits and develops on the introduced weedy vine, Passiflora foetida and the native vine, Adenia heterophylla (both Passifloraceae). Passiflora foetida has multiple minuscule extrafloral nectaries on its leaf margins, and A. heterophylla has two prominent extrafloral nectaries at the base of the petiole and underside of

Invasive ants reduce abundance of small rainforest skinks

“…The near absence of small skinks in high yellow crazy ant sites and limited differences in skink prey among site categories suggest that yellow crazy ants have directly affected the smaller skinks, rather than indirectly affected them via reducing prey. When yellow crazy ants are abundant, they are capable of harassing and, sometimes killing, invertebrate and vertebrate organisms much larger than they are (Davis et al 2010;Dorrestein et al 2019;Lach et al 2016;O'Dowd et al 2003;Plentovich et al 2018). With their formic acid spray, the ants can blind or maim organisms such as red land crabs (O'Dowd et al 2003) and wedgetail shearwater chicks (Plentovich et al 2018), and then prey on them or leave them susceptible to starvation.…”

Ant assemblage composition explains high predation pressure on artificial caterpillars during early night

“…For example, Lach et al . () found that one ant species, Anoplolepis gracilipes , exerted 4.4–16.0 times greater predation rate than other co‐occurring ant species of tropical forests. In their study, A. gracilipes was considered to be a ‘super’ predator.…”

Alien Species and Insect Conservation

“…In part, this was apparently because management of the cacao crop had negative impacts on native ants that depend on trees for nesting and foraging (Bos et al 2008 ). That A. gracilipes increases its aggressive behaviour and recruitment to foraging sites as extrafl oral nectar supply increases was used by Lach et al ( 2015 ) to evaluate its impact on an Australian native butterfl y, Vindula arsinoe (Nymphalidae) in the Wet Tropics rainforest of northern Australia. Relative ant richness in natural forest (40 species) and in cacao plantations (66 species) implied the value of the latter system, but many of the former group (treated as more specialised 'forest species') did not occur in the cacao areas.…”