Parasitoids follow herbivorous insects to a novel host plant, generalist predators less so

Abstract

The ‘enemy‐free space’ hypothesis predicts that herbivorous insects can escape their natural enemies by switching to a novel host plant, with consequences for the evolution of host plant specialisation. However, if natural enemies follow herbivores to their novel host plants, enemy‐free space may only be temporary. We tested this by studying the colonisation of the introduced tree Eucalyptus grandis (Hill) Maiden (Myrtaceae) by insects in Brazil, where various species of herbivores have added eucalyptus to their host plant range, which consists of native myrtaceous species such as guava. Some herbivores, for example, Thyrinteina leucoceraea Ringe (Lepidoptera: Geometridae), cause outbreaks in eucalyptus plantations but not on guava, possibly because eucalyptus offers enemy‐free space. We sampled herbivores (mainly Lepidoptera species) and natural enemies on eucalyptus and guava and assessed parasitism of Lepidoptera larvae on both host plant species during ca. 2 years. Overall, predators were encountered more frequently on guava than on eucalyptus. In contrast, parasitoids were encountered equally and parasitism rates of Lepidoptera larvae were similar on both host plants. This indicates that herbivores may escape some enemies by moving to a novel host plant. However, this escape may be temporary and may vary with time. We argue that studying temporal and spatial patterns of enemy‐free space and the response of natural enemies to host use changes of their herbivorous prey is essential for understanding the role of natural enemies in the evolution of host plant use by herbivorous arthropods.

Use of an exotic host plant shifts immunity, chemical defense, and viral burden in wild populations of a specialist insect herbivore

“…While optimization of herbivore performance, as measured by bitrophic indices focusing solely on the herbivore–plant interaction, often fails to explain patterns of host plant use (Forister et al, 2009; Mason et al, 2011), persistence on novel host plants involves an array of ecological, behavioral, and physiological factors beyond suitability for development (Forister & Wilson, 2013; Mason, 2016). In particular, herbivore interactions with natural enemies, including predators (Grosman et al, 2017; Murphy, 2004), parasitoids (Fortuna et al, 2013; Harvey & Fortuna, 2012), and pathogens (Cory & Hoover, 2006; Shikano, 2017) can differ substantially between native and exotic host plant species. As these interactions comprise a major source of mortality for insect herbivores (Hawkins et al, 1997), exploitation of enemy‐free or enemy‐reduced space may constitute an important driver of host range evolution (Bernays & Graham, 1988; Jeffries & Lawton, 1984; Singer & Stireman, 2005).…”

Pesticide resistance in arthropods: Ecology matters too

“…If a phytophagous species uses those new allelochemicals to defend against parasitoids and predators (compare Harvey et al, 2010; Bezemer et al, 2014), through sequestration (Beran & Petschenka, 2022), the efficiency of its natural enemies may be affected. This could have suppressed or released effects on the herbivore, depending on whether the higher trophic levels have advantages or disadvantages from the novel host traits (compare Harvey et al, 2010; Grosman et al, 2017), and may lead to further evolutionary responses between the host and the natural enemy. Moreover, an altered host plant range in herbivorous pollinators such as within Lepidoptera may affect plant–insect mutualisms and their ecosystem service capacity.…”

Species composition of arthropods on six understory plant species growing in high and low light conditions

“…In our research, generalists and specialists were represented by G. quinquepunctata and A. brevicollis coryletorum, respectively. According to Grosman et al (Grosman et al, 2017) predators follow herbivorous insects to a new host plant slower and to a lesser extent than do parasites. They also concluded that predator movement is a matter of time and in the long run, predators will also adapt to hunting herbivores on a new host plant.…”