Role of areoles on prey abundance and diversity in the hooded pitcher plant (<Emphasis Type="Italic">Sarracenia minor</Emphasis>, <Emphasis Type="Italic">Sarraceniaceae</Emphasis>)

The hooded pitcher plant, Sarracenia minor, is a carnivorous facultative wetland species native to the southeastern USA and is listed as threatened by the state of Florida. Pitchers of S. minor possess white, semitranslucent spots (areoles), which have been hypothesized to aid in the capture of prey (= visual lures) by increasing the amount of light entering the back of the hood, which persuades insects to enter and fall into the base of the pitcher. In this study, the role of the areoles in prey capture abundance and diversity were experimentally investigated under variable lighting conditions in situ. Plants in two populations experiencing different light intensities, which varied in the amount of canopy cover and incident light reaching the plants, were experimentally manipulated by coloring varying percentages of areoles, ranging from 0 to 100 % (in increments of 25 %), with indelible ink. After 2 months, pitchers were collected and dissected to determine the number and identity of prey captured (approximately 18,000 prey were sampled). Although total prey abundance was approximately five times higher at McGirt’s Creek (sunny site) compared to UNF (shaded site), the effect of areoles on prey capture rates and biodiversity was site dependent. Reducing the number of visual lures of plants at the sunny site produced a significant decrease in the number of prey captured, but prey biodiversity (community composition) was unaffected. However, total prey capture was unaffected at the shaded site, while prey biodiversity was negatively correlated with the percent of areoles colored. Results from the current study suggest that areoles conditionally act as visual lures, but their overall importance is dependent on local environmental variables—especially canopy cover and the amount of incident sunlight reaching the plants.     

Coffee volatiles induced after mechanical injury and beetle herbivory attract the coffee berry borer and two of its parasitoids

The coffee berry borer (CBB), Hypothenemus hampei (Ferrari), is the most important insect pest of coffee worldwide. In this study, we used headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry to sample and identify volatile compounds from Robusta coffee berries, Coffea canephora Pierre ex Froehner, infested with CBB and with mechanical damage. Furthermore, we evaluated the behavioral responses of the CBB and two of its parasitoids, Prorops nasuta Waterstone and Phymastichus coffea LaSalle, to three selected coffee volatile compounds in a Y-tube olfactometer. We found in the effluvia of red coffee berry compounds not previously reported for this coffee species. Our results show that Robusta coffee berries release induced volatiles either by insect herbivory or by mechanical damage. Small amount of butyl acetate, unknown compound 2, α-longipinene, longiborneol and longiborneol acetate are produced only in infested coffee berries fruits. Quantitatively, nine compounds account for the difference between healthy berries, infested, or mechanically damaged berries. Trans-ocimene, 4,8-dimethyl-3,7-nonadien-2-ol, α-copaene and kaurene increased amount levels in infested berries, while amount of methyl salicylate and linalool increased in mechanically damaged coffee berries. The olfactometric bioassays showed that CBB females and its two parasitoids were attracted to methyl salicylate. In addition, H. hampei and P. nasuta were attracted to linalool, and P. nasuta and P. coffea were attracted to trans-ocimene.     

Potential for oilseed rape resistance in pollen beetle control

Breeding for plant resistance to insect pests is a classic strategy in integrated management, but it has never been developed for use against European pests of oilseed rape (Brassica napus) (OSR), especially one of the most damaging ones, the pollen beetle (Meligethes aeneus). In this paper we look at the three strategies that could be employed to improve OSR resistance (based on transgenes, relatives of B. napus or OSR natural variation) and review our current knowledge as to how these strategies could be put into practice. We identify the drawbacks which are specific to the pollen beetle that could impede breeding programs for resistance, and propose an approach to circumvent them. Finally, we detail the steps of the interaction between OSR and the pollen beetle that could be targeted in order to improve plant resistance (host plant location, adult survival, adult feeding, egg production and oviposition, larval development) and discuss their efficiency and durability potential.     

What if we lose a hub? Experimental testing of pollination network resilience to removal of keystone floral resources

On the basis of theoretical predictions, pollination networks seem to be resilient to random node elimination but sensitive to targeted exclusion. However, such predictions have a very weak empirical basis. In order to test the robustness of the pollination network to short-term disturbances, we removed inflorescences of the most connected species occurring in a lowland meadow network using the before–after approach and compared the result with that obtained by network modelling. The manipulated network showed no significant differences for the most commonly used metrics, but was more generalized than control networks, owing to a change in the preferences of pollinators. Furthermore, no secondary extinctions (emigrations) were found, owing to the considerable natural variation found among insect species assemblages. Following elimination of the most linked plant species, a new hub was detected in the experimental meadow, the hub node being a plant species with a similar inflorescence to that removed, and formerly playing the role of a peripheral node. We conclude that exclusion of the main food source forced insects to change their specialized preferences to other plant species that were available. Mostly, these had inflorescences similar to those that were removed.     

Interspecific differences in milkweeds alter predator density and the strength of trophic cascades

Trophic cascades occur when predators benefit plants by consuming herbivores, but the overall strength of a trophic cascade depends upon the way species interactions propagate through a system. For example, plant resistance to, or tolerance of, herbivores reduces the potential magnitude of a trophic cascade. At the same time, plants can also affect predator foraging or consumption in ways that either increase or decrease the strength of trophic cascades. In this study, we investigated the effects of plant variation on cascade strength by manipulating predator access to aphid populations on two species of milkweed: the slower-growing, putatively more-defended Asclepias syriaca and the faster-growing, putatively less-defended Asclepias incarnata. Predatory insects increased plant growth and survival for both species, but the strength of these trophic cascades was greater on A. incarnata, which supported more aphid growth early in the season than did A. syriaca. More predators were observed per aphid on A. incarnata, and cage treatments generated significant patterns consistent with predator aggregation on A. incarnata, but not A. syriaca. Although predators strongly affected aphids, this effect did not differ consistently between milkweed species. Plant tolerance to herbivory may therefore be the primary driver of the difference in trophic cascade strength observed. Importantly, we observed that the timing of predator exclusion affected plant growth and survival differently, indicating that measures of “cascade strength” may change with phenology and plant physiological responses. Together, our results suggest a mechanism by which differences in resource allocation patterns could explain differences in growth, phenology, and cascade strength between species.