Thigmomorphogenetic responses occur in many environmental settings. The most pronounced effects are found under conditions of extremely high rates of turbulent wind or water flow. However, it is an ubiquitous phenomenon, since mechanical perturbations are to be encountered under all but the most stringent laboratory conditions. Our present understanding of these phenomena is the result of studies at the ecological, anatomical, physiological, biochemical, biophysical and molecular biological levels.
The unique benefits of wild pollinators to the productivity of agricultural crops have become increasingly recognized in recent decades. However, declines in populations of wild pollinator species, largely driven by the conversion of natural habitat to agricultural land and broad-spectrum pesticide use often lead reductions in the provision of pollination services and crop production. With growing evidence that targeted pollinator conservation improves crop yield and/or quality, particularly for pollination specialist crops, efforts are increasing to substitute agriculturally intensive practices with those that alleviate some of the negative impacts of agriculture on pollinators and the pollination services they provide, in part through the provision of suitable pollinator habitat. Further, similarities between the responses of some pollinators and predators to habitat management suggest that efforts to conserve pollinators may also encourage predator densities. We evaluated the effects of one habitat management practice, the addition of cacao fruit husks to a monoculture cacao farm, on the provision of pollination services and the densities of two groups of entomophagous predators. We also evaluated the impacts of cacao fruit husk addition on pollen limitation, by crossing this habitat manipulation with pollen supplementation treatments. The addition of cacao fruit husks increased the number of fruits per tree and along with hand pollination treatments, increased final yields indicating a promotion of the pollination ecosystem service provided by the specialist pollinators, midges. We also found that cacao fruit husk addition increased the densities of two predator groups, spiders and skinks. Further, the conservation of these predators did not inhibit pollination through pollinator capture or deterrence. The findings show that, with moderate habitat management, both pollinator and predator conservation can be compatible goals within a highly specialized plant-pollinator system. The effectiveness of this habitat manipulation may be attributable to the increased availability of alternative habitat and food resources for both pollinators and predators. The results exemplify a win-win relationship between agricultural production and biological conservation, whereby agricultural practices to support vital pollinators and pollination services can increase production as well as support species conservation.
Ecosystem service‐driven methods of agricultural production that make optimal use of an ecosystem's natural services are often effective in smallholder crops, leading increases in habitat heterogeneity at large spatial scales that encourage beneficial species. Pollination services in cacao farms can be enhanced through efforts to conserve pollinator habitats, such as adding cacao fruit husks underneath trees to provide habitat and food resources for midge pollinators. However, it remains unclear how this habitat manipulation affects pest densities or biological control. Here, we evaluated the effects of the predaceous ant Oecophylla smaragdina on three major pests of Australian cacao (Helopeltis spp., Amblypelta spp., and Rhyparida nitida) in an Australian cacao farm, in the presence and absence of cacao fruit husks. We also evaluated the effect of O. smaragdina on their potentially plant‐damaging, mutualistic mealybug (Pseudococcidae) partners in the presence and absence of cacao fruit husks. Oecophylla smaragdina reduced the combined densities of Helopeltis spp. and Amblypelta spp., regardless of cacao fruit husk addition. The ants also reduced the densities of R. nitida in the absence of cacao fruit husks, but R. nitida densities were naturally low in the experimental plots that received the addition of cacao fruit husks, regardless of ant presence. In contrast, ants generally increased the densities of mealybugs. These data suggest that O. smaragdina ants provide pest control services for three major insect pests in Australian cacao farms. Furthermore, this control may be compatible with habitat manipulations (i.e., the addition of cacao fruit husks) to improve pollinator habitat.
Most plant species depend upon insect pollination services, including many cash and subsistence crops. Plants compete to attract those insects using visual cues and floral odor which pollinators associate with a reward. The cacao tree, Theobroma cacao, has a highly specialized floral morphology permitting pollination primarily by Ceratopogonid midges. However, these insects do not depend upon cacao flowers for their life cycle, and can use other sugar sources. To understand how floral cues mediate pollination in cacao we developed a method for rearing Ceratopogonidae through several complete lifecycles to provide material for bioassays. We carried out collection and analysis of cacao floral volatiles, and identified a bouquet made up exclusively of saturated and unsaturated, straightchain hydrocarbons, which is unusual among floral odors. The most abundant components were tridecane, pentadecane, (Z)-7pentadecene and (Z)-8-heptadecene with a heptadecadiene and heptadecatriene as minor components. We presented adult midges, Forcipomyia sp. (subgen. Forcipomyia), Culicoides paraensis and Dasyhelea borgmeieri, with natural and synthetic cacao flower odors in choice assays. Midges showed weak attraction to the complete natural floral odor in the assay, with no significant evidence of interspecific differences. This suggests that cacao floral volatiles play a role in pollinator behavior. Midges were not attracted to a synthetic blend of the above four major components of cacao flower odor, indicating that a more complete blend is required for attraction. Our findings indicate that cacao pollination is likely facilitated by the volatile blend released by flowers, and that the system involves a generalized odor response common to different species of Ceratopogonidae.
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