Evidence that insect herbivores are deterred by ant pheromones

Abstract

It is well documented that ants can protect plants against insect herbivores, but the underlying mechanisms remain almost undocumented. We propose and test the pheromone avoidance hypothesis-an indirect mechanism where insect herbivores are repelled not only by ants but also by ant pheromones. Herbivores subjected to ant predation will experience a selective advantage if they evolve mechanisms enabling them to avoid feeding within ant territories. Such a mechanism could be based on the ability to detect and evade ant pheromones. Field observations and data from the literature showed that the ant Oecophylla smaragdina distributes persistent pheromones throughout its territory. In addition, a laboratory test showed that the beetle Rhyparida wallacei, which this ant preys on, was reluctant to feed on leaves sampled within ant territories compared with leaves sampled outside territories. Thus, this study provides an example of an ant-herbivore system conforming to the pheromone avoidance hypothesis.

Species Richness of Arboreal Ant Assemblages (Hymenoptera, Formicidae) and Frequency of <em>Oecophylla Smaragdina </em>(Fabricius) Occurrence in A Wet Zone Cashew (<em>Anacardium Occidentale L.</em>) Field in Sri Lanka

“…The presence of 14 ant species including O. smaragdina provided an insight into the importance of their presence on cashew trees with regard to the absence of major insect pests during the phenological cycle because damage symptoms were not reported in the cashew field (personal observation, second author; personal communication, cashew field owner). According to Offenberg et al (2004) interspecific pheromones of the ants may have repelled the cashew pests. Rickson & Rickson (1998) reported 8-11 species of ants including A. gracilipes, C.…”

The search rate of the African weaver ant in cashew

“…The Search Rate of the African Weaver Ant in Cashew Introduction control agents in fruit trees, such as mango and cashew (Way & Khoo, 1992;Peng et al, 1999a;Offenberg et al, 2004;Peng & Christian, 2006;Dwomoh et al, 2009) Dwomoh et al (2009) showed that O. longinoda was as effective in protecting cashew against pest insects as insecticides such as l-cyhalothrin and cypermethrin + dimethoate. Several studies suggest that with appropriate management weaver ants can significantly increase fruit yield and reduce the use of pesticides (Van Mele, 2008).…”

Effect of Formica aserva Forel (Hymenoptera: Formicidae) on ground dwelling arthropods in central British Columbia.

“…Some insects may also have the ability to detect the chemical signals associated with ants. For example, A. bipunctata beetles are able to adjust their behaviour in response to L. niger semiochemicals (Oliver et al, 2008), and Offenberg et al (2004) found that chrysomelid beetles (Rhyparida wallacei Baly) preferentially fed on leaves collected from trees absent of Oecophylla smaragdina …”

“…Gonsalves et al (2005) also found that predatory ants had a negative effect on termite activity, while non-predatory ants did not, suggesting that predation by ants may be an important disturbance factor in some ecosystems. In some cases, direct interactions with ants may not be required for them to influence other arthropods (Offenberg et al, 2004;Oliver et al, 2008). Artificially low Formica aquilonia Yarrow ant densities created by Laakso and Setala (2000) also resulted in increased activity of other predatory arthropods, which they described as a compensatory shift in the predatory invertebrate guild.…”

“…Most ant species use pheromone trails (Offenberg et al, 2004), which they typically detect and follow when they're in a gaseous state, creating what Holldobler and Wilson (1990) described as "vapor tunnels". In the sub-family Formicinae these trails are emitted from the hind gut o f workers (Parry & Morgan, 1979) and in red wood ants these signals can persist for long periods (Rosengren & Fortelius, 1987 and references therein).…”