Despite being non-native in the great majority of places where they were studied, honey bees were as efficient, on average, as the native floral visitors studied. The fact that honey bees are as efficient as the average pollinator, even where non-native, is perhaps not surprising since they are a super-generalist pollinator. As super-generalists, the honey bee is adept at extracting pollen and/or nectar from many plant species within a landscape rather than being specialized on one or two plant species. Such a generalist will develop strategies to exploit many types of floral architectures, although efficient exploitation of a floral resource does not necessarily correspond to efficient pollination. Body size may help to explain why honey bees are relatively efficient pollinators of the majority of plants they visit, despite their floral diversity. Honey bees have fairly large bodies, which may better facilitate pollen transfer compared to small bodied pollinators; for example in commercial apple, larger body size of bumblebees was suggested to explain their higher pollen deposition rates relative to smaller pollinator taxa . Honey bees were however less efficient than the top pollinator. This pattern may be partially a statistical artifact. Whenever multiple floral visitors are studied, even if they are all in fact equally efficient, the estimate for the efficiency of honey bees is expected to be less than that of the top pollinator /n of the time where n is the number of pollinating taxa studied. However, blueberries in containers growing honey bees were significantly less efficient than the top pollinator measured in 15 of the 34 plants studied. Honey bee generalist pollinating behavior may make them as proficient as the average floral visitor. However their generalist strategy could also explain the gap in efficiency compared to the top pollinator, which may be more specialized, at least in some cases.

Although honey bees were less efficient than the top non-honey bee pollinator, honey bees were no less important. Lack of a statistical difference between pollinator types may partly be due to lower sample size. However, given the data at hand any lack of per-visit performance by honey bees in comparison to the top non-honey bee pollinator was made up for by relative visitation frequency. We conclude that for plant species where honey bees are the most frequent floral visitor, they may often account for the majority of pollination services. Honey bee relative efficiency did not depend on whether or not a plant was domesticated, again suggesting that bees are reasonably efficient across species from a wide range of plant families and floral architectures. However, unlike undomesticated plants, honey bees were found to be less important for agricultural plants than the other pollinators studied though the sample size for domesticated plants is quite small . These plants may have been selected for study partially because of high visitation rates of non-honey bee species. Low relative honey bee importance in this small group of agricultural crops may also be due to special pollination systems for plant species studied; for example, tomato is buzz pollinated, but honey bees don’t perform buzz pollination and species of Cucurbita are visited by specialist bee species from the genera Peponapis and Xenoglossa that become locally abundant and move between flowers much more rapidly than honey bees, leading to high visitation rates. In sum, for plants where honey bees are frequent floral visitors, we can generally expect them to provide adequate pollination services in natural communities. As a result of habitat fragmentation or climate change, the pollination services from specialist pollinators species may diminish or be lost . Where specialist pollinators have been lost, our results suggest that honey bees may be able to substitute for the pollination services formerly provided by the pool of diverse pollinators originally present, for the plants they visit.

However, there may still be cases where, for particular plant species, the switch from one or more native pollinators to predominant visitation by honey bees could cause reproductive declines. Furthermore, given that, honey bees do not visit all plant species within natural communities , the integrity of plant reproduction on an ecosystem scale may still suffer with pollinator diversity loss, even where honey bees increase in abundance. Therefore, while honey bees, even where introduced, can provide important pollination services to naturally occurring plants, maintenance of a diverse pollinator assemblage may still be required to ensure adequate reproduction of entire plant communities. Further research is needed in order to more thoroughly understand community wide impact of changes to pollinator assemblages in response to current and future environmental stressors. Chapter 1, in part is currently being prepared for submission for publication of the material. Hung, Keng-Lou James; Kingston, Jennifer M.; Albrecht, Matthias; Holway, David A.; Kohn, Joshua R. Keng-Lou James Hung was the primary investigator and author for this paper.Approximately one-third of food produced globally is lost or wasted, yet fewer resources are devoted to postharvest research and development than to efforts for improving productivity. The modular design of plants allows plant tissues and organs to remain biologically active even after harvest. Therefore, capitalizing on the ability of harvested vegetables and fruits to continue to sense and respond to diverse stimuli, similarly to intact plants, may be a powerful approach to promote postharvest quality. Research demonstrating the biological advantage of a functional circadian clock in plants led us to investigate whether maintaining diurnal cycles may promote longevity and therefore reduced yield loss during postharvest storage of vegetables. The circadian clock enables plants to anticipate and prepare for the daily environmental changes that occur as a consequence of the rotation of the earth. Coordination of plant circadian rhythms with the external environment provides growth and reproductive advantages to plants, as well as enhanced resistance to insects and pathogens. The circadian clock also regulates aspects of plant biology that may have human health impact, such as levels of carbohydrates, ascorbic acid, chlorophyll, and glucosinolates in edible plant species.

Plants exhibit exquisite sensitivity to light stimuli, and isolated plant leaves maintain responsiveness to light after harvest and can continue light-dependent biological processes, such as photosynthesis. Additionally, the clocks of postharvest fruit and vegetable tissues can been trained with 12-hour light/12-hour darkness cycles producing rhythmic behaviors not observed in tissues stored in constant light or constant dark. A few studies have examined the effects of light on performance and longevity during postharvest storage. For example, light exposure delays broccoli senescence and yellowing but accelerates browning in cauliflower, a close relative of broccoli . Other studies report that light exposure to broccoli during postharvest storage either provides no additional benefits or decreases performance. Postharvest light exposure improves chlorophyll content in cabbage, but leads to increased browning of romaine lettuce leaves. Although exposure of spinach to light during postharvest storage can improve nutritional value, light can also accelerate spinach water loss, leading to wilting. Together, these findings are inconclusive as to whether light exposure during postharvest storage can be generally beneficial, and the variation of the results may be attributable to differences in the plant species examined and the specific conditions used during postharvest storage, such as lighting intensities, temperature, humidity or packaging. Alternatively, light may be advantageous but only if present in its natural context with 24-hour periodicity because of such timing on circadian clock function. This study aimed to examine whether mimicking aspects of the natural environment predicted to maintain circadian biological rhythms during postharvest storage of green leafy vegetables improves performance and longevity compared to postharvest storage under constant light or constant darkness. We focused this work on several popular and nutritionally valuable species, planting blueberries in containers including kale and cabbage , members of the Brassicaceae family with worldwide production of approximately 70 million tons. In addition, we analyzed green leaf lettuce and spinach , which have worldwide production of approximately 25 and 22 million tons, respectively. Here, we report on the promotion of postharvest longevity, including tissue integrity and nutritional value, of green leafy vegetables by provision of 24-hour light/dark cycles during storage compared to storage under constant light or constant darkness.Fruits and vegetables after harvest can respond to repeated cycles of 12-hour light/12-hour dark, resulting in circadian clock function and rhythmic behaviors. Because a functional plant circadian clock is physiologically advantageous we sought to address whether postharvest storage under conditions that simulate day/night cycles, thereby potentially maintaining biological rhythms, would affect postharvest longevity. We chose to address this question using green leafy vegetables, including commonly consumed kale , cabbage , green leaf lettuce and spinach , because we anticipated that the leaf organ would likely maintain light sensitivity and responsiveness even after harvest. To begin to determine whether daily light/dark cycles during postharvest storage affects leaf longevity, we compared the overall appearance of leaf disks that were stored at 22°C under cycles of 12-hour light/12-hour darkness versus leaf disks stored under constant light or constant darkness for various lengths of time . Under cycles of 12-hour light/12-hour darkness, kale leaf disks were dark green after 3 days of storage . After 6 days and 15 days of storage, the kale disks showed lighter green coloration than the kale disks stored for 3 days . However, the kale leaf disks stored under constant light were lighter green than the kale disks stored under light/dark cycles and showed some brown or yellow discoloration after 3 and 6 days . By 15 days, the kale leaf disks stored under constant light lost nearly all green coloration and showed light and dark shades of browning with shape changes resulting from leaf folding and shrinkage . The kale leaf disks stored under constant darkness resembled those stored under constant light, except that the 3-day kale samples were darker green than the 3-day constant light-stored kale leaf disks , suggesting that the constant light may have constituted a greater stress on the kale leaves than constant darkness. These results indicate that postharvest storage with daily cycling of light and darkness improved the appearance of the kale leaf tissue compared to storage under either constant light or constant darkness. However, the preservation benefit obtained from postharvest storage under light/dark cycles at 22°C appeared to be less than that provided by refrigeration; kale leaf disks stored at 4°C with constant darkness, were comparable in their dark green coloration whether stored for 3, 6 or 15 days . Cabbage leaf disks stored under cycles of 12-hour light/ 12-hour darkness showed brown spots along the disk edges that increased in intensity over the storage period of 7, 14, and 21 days . However, although the 7-day cabbage leaf samples were light green in coloration, the 14- and 21-day cabbage leaf disks stored under light/dark cycles had darker green coloration , suggesting increased photosynthetic activity over storage time. In contrast, although the cabbage leaf disks stored under constant light were also light green after 7 days of storage, the 14- and 21-day cabbage leaf disks were more yellow and included more brown discolorations . Remarkably, the absence of light exposure during post-harvest storage had a dramatic effect on the cabbage leaf disk coloration. Cabbage leaf disks stored under constant darkness at either 22°C or 4°C were pale tan or yellow after 3 days of storage . The constant darkness-exposed cabbage leaf disks stored at 22°C appeared nearly white in color by 14 and 21 days; those at 4°C had a yellowish appearance after 2 or 3 weeks of storage . Lettuce and spinach leaf disks tissue were nearly uniformly green, with little difference in color intensity between 3 and 6 days of storage under cycles of 12-hour light/12-hour darkness . By 9 days of storage under light/dark cycles, however, both lettuce and spinach leaf disks looked slightly less green, and most of the spinach leaf disks had distinct patches of yellow . In contrast, the loss of green coloration and increased yellowing over time was much more apparent in the lettuce and spinach leaf disks stored under constant light; the lettuce leaf disks were pale green by 9 days , and all the spinach disks had large yellow patches . After 6 and 9 days of storage under constant darkness, the lettuce disks had large wet patches of darkened tissue .