Abstract
In the Cerrado, many plants are patrolled by ants, but in some cases, predatory wasps may also play an important role in herbivore deterrence. Here we examined the effects of the wasp Brachygastra lecheguana and the ant Pseudomyrmex gracilis on the predation of endophytic weevils which develop in the flower buds of Ouratea spectabilis trees. We (i) compared frequency and the abundance of weevils preyed upon by wasps; (ii) possible synergic effects of ants and wasps in decreasing weevil population; and (iii) whether wasps preyed upon weevils in more visible, easy-access inflorescences, i. e. those located in edges of canopy. In contrast to ants, wasps were observed significantly more frequently on O. spectabilis and were responsible for 88% of the weevil larvae preyed upon. Plants visited by both B. lecheguana and P. gracilis had a substantial reduction in weevil larvae compared to plants visited by B. lecheguana only. This indicates a complementary effect of predators with distinct skills in deterring the weevil population; however, ants were responsible for only a small portion of weevils preyed upon. Weevil larvae occurred evenly in both visible and hidden inflorescences; nonetheless, wasps predominantly visited inflorescences located on the edges of the canopy. In this ecological system, predatory wasps played a substantial part in weevil deterrence and can be considered a better plant-guard than ants.
Highlights
In the Brazilian savanna, many plant species are severely attacked by a wide range of herbivorous insects, which feed and inflict damage on virtually every plant part, especially leaves and flowers (Price et al, 1995; Bächtold et al, 2012; Vilela et al, 2014)
In the first week of observation, adult weevils were frequently observed engaged in mating behavior in inflorescences of O. spectabilis, so we considered that the following week was the period in which weevil larvae might be under development inside flower buds
The number of adult weevils was higher at the beginning of the study, during the weevil reproductive season (Fig 2A), but as the season progressed and flower buds became scarce (Fig 2B), the abundance of adult Anthonomus gradually decreased (H3 = 37.2098; P< 0.0001)
Summary
In the Brazilian savanna, many plant species are severely attacked by a wide range of herbivorous insects, which feed and inflict damage on virtually every plant part, especially leaves and flowers (Price et al, 1995; Bächtold et al, 2012; Vilela et al, 2014). Many plants present biotic protection against herbivores, in the form of aggressive and predatory ant-guards, which feed on extrafloral nectaries (EFNs) and protect the plant against assorted types of insects, especially folivores (Koptur et al, 1998; Bronstein et al, 2006; Alves-Silva, 2011; Heil, 2015). Predator behavior can be affected by plant structural complexity, which confers more hiding places for herbivores (Lawton, 1983), or restrains the foraging activity of herbivores’ natural enemies (Hopper, 1984; Andow & Prokrym, 1990). As shown by Del-Claro et al, (1997) the presence of natural enemies and/or the likelihood of being preyed upon, influence the behavior of herbivores, and they may seek habitats that confer some type of protection and less risk of being encountered by predators (Bächtold & Alves-Silva, 2013). The social Polistinae wasp Brachygastra lecheguana Latr. (Hymenoptera: Vespidae) is the main predator
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