We used a one-sample t-test to test the null hypothesis that the pollination efficiency of honey bees equals the efficiency of the average non-honey bee floral visitor . Since honey bee relative efficiency did not differ between agricultural and wild plant species , data from all plant species were combined. The best multiple regression model selected from a set of candidate models of environmental variables revealed that the network-level frequency of visits by honey bees is positively related to the first principal component of temperature bioclimatic variables , where higher values correspond with higher overall temperature, higher isothermality, lower annual range and lower seasonality . Honey bees were also more frequent floral visitors in mainland networks compared to island networks . Perhaps surprisingly, our regression model revealed no effect of the honey bee’s native status on honey bee numerical importance . Release from pathogens and parasites often contributes to the success of introduced species ; this factor may be unimportant in honey bees because many of their pathogens have spread worldwide due to trafficking of domestic colonies . Nevertheless, it is noteworthy that eight of the ten networks with the highest relative frequency of honey bee visits come from introduced range localities, and that in five of these networks, honey bees accounted for more than half of the total visits recorded . While Abe et al. found that honey bee dominance in the Ogasarwara satellite islands was driven by an introduced lizard’s preferential predation on native pollinators, black plastic garden pots further studies are needed to understand why honey bees reach high abundance in some parts of their introduced range, but not others.
Also surprising is our finding that study year was unrelated to honey bee numerical importance , given the high mortality in managed honey bee colonies reported over the last two decades . Agents responsible for increased mortality in managed colonies can also affect wild or feral honey bee colonies , but ongoing research also reveals the resilience of unmanaged honey bee populations to mortality agents such as parasites and pathogens . In our pollination networks, the degree to which honey bee individuals are coming from managed versus unmanaged colonies likely varies based on geographical location and proximity of the study site to agriculture. However, in one network with high honey bee numerical importance , genetic testing indicated that the majority of the honey bee foragers were derived from feral, Africanized hives . Although honey bees are numerically dominant pollinators in many networks, their importance as floral visitors to individual plant species varies widely. An examination of 46 pollination networks that provide data on each studied plant species yielded 1629 plant taxa within these networks. While some plant taxa species are found in more than one network, we treat each plant species within each network independently because our goal is to examine the frequency with which honey bees visit each plant species within discrete communities. Across these 1629 plant taxa, we found a strongly, positively skewed distribution of honey bee visitation frequency . Honey bees were the only documented visitors of 5.34% of plant taxa , and contributed the majority of visits to 15.16% of plant taxa . However, honey bees also failed to visit the majority of plant taxa .
Restricting the analysis to plant taxa with ³ 10 visits recorded to minimize extreme values due to low sample size did not qualitatively affect our results . In this data subset, honey bees were the sole documented visitors of 3.44% of plant taxa , contributed the majority of visits to 17.84% of plant taxa , and failed to visit 50.31% of plant taxa . Our finding that honey bees numerically dominated a number of plant taxa is perhaps unsurprising given their ability to recruit nest mates to spatially and temporally abundant floral resources . However, it is noteworthy that this pattern holds true in their introduced range, where floral resources monopolized by honey bees presumably coevolved with native pollinators. This analysis cannot distinguish whether honey bees dominate certain floral resources because they displace other pollinators or because they have the ability to profit from floral resources not valued by other pollinators. However, the data do suggest that honey bees possess the potential to disrupt interactions between plants and other pollinators in the majority of natural communities in which they occur. On the other hand, our finding that honey bees are frequent floral visitors to only a small subset of the plant species in a community is consistent with studies investigating honey bee colony-level resource use and underscores the importance of maintaining robust, diverse communities of non-honey bee pollinators for the persistence of the majority of plant species in natural communities. While our analyses of pollination networks worldwide reveal that honey bees are exceptionally abundant and generalized floral visitors, our analysis of pollination efficiency of honey bees reveals that they are average pollinators with respect to their pollination efficiency . Using a dataset of 35 plant species spanning 23 plant families that exhibit a diversity of flower sizes, shapes, and colors, we compared honey bees and non-honey bee floral visitors with respect to seed set, fruit set, or pollen deposition resulting from single floral visits . The relative pollination efficiency of honey bees did not differ between the 16 agricultural and 19 non-agricultural plant species , perhaps because flowers of agricultural species , squash , tomato often closely resemble those of their wild relatives. Overall, we found no evidence that the pollination efficiency of honey bees consistently differs from that of the average of the non-honey bee floral visitors considered in these studies . Since the importance of a particular pollinator to a given plant species is often calculated as its per-visit efficiency multiplied by its visitation frequency , it seems reasonable, given our results, to assume that the ecological importance of honey bees as pollinators in any community is satisfactorily estimated by their visitation frequency. However, since honey bees are known to exhibit poor efficiency at pollinating certain plant taxa , we caution that careful studies are needed to demonstrate the importance of honey bees as pollinators to particular plant species. Further, in at least one case, high visitation frequency by a pollinator damaged raspberry flowers and led to reduced reproductive success . On plant species and in plant communities where honey bees reach high visitation rates, a similar negative relationship between visitation frequency and plant reproductive fitness may occur and is worthy of investigation . As a numerically dominant, super-generalist pollinator, honey bees may influence the fitness and behavior of competing pollinators, enhance as well as reduce plant fitness, and facilitate the spread of non-native weeds and pathogens . Given the ecological importance of honey bees, there is little doubt that changes in their distribution and abundance will impact the evolutionary trajectory of co-occurring mutualists and competitors, and likely the long-term eco-evolutionary dynamics of communities in which they take part. Our results underscore the urgent need for more data on how honey bees, and the potential loss thereof, shape the ecology and evolution of plant-pollinator interactions on global and local scales.Drosophila suzukii Matsumura is an economic pest of small and stone fruit in major production areas including North America, Asia and Europe. Female D. suzukii oviposit into suitable ripening fruits using a serrated ovipositor. This is unique compared to other drosophilids, square plastic plant pots including the common fruit fly, D. melanogaster, which oviposit into overripe or previously damaged fruit. Developing fruit fly larvae render infested fruit unmarketable for fresh consumption and may reduce processed fruit quality and cause downgrading or rejection at processing facilities. In Western US production areas, D. suzukii damage may cause up to $500 million in annual losses assuming 30% damage levels, and $207 million in Eastern US production regions.
Worldwide, the potential economic impacts of this pest are staggering. Pesticide applications have been the primary control tactic against D. suzukii both in North America and in Europe. The most effective materials are those that target gravid females, including pyrethoids, carbamates, and spinosyns. These applications are timed to prevent oviposition in susceptible ripening host crops. In the Pacific Northwest, many growers have adopted scheduled spray intervals of 4–7 days. This prophylactic use of insecticide is unsustainable as growers have a limited selection of products and modes of action. This could ultimately lead to D. suzukii becoming resistant and may cause secondary pest problems because of negative effects on beneficial organisms. Furthermore, production costs have increased substantially in crops where D. suzukii must be managed. Effective sampling methodology for D. suzukii is lacking despite extensive efforts to improve trap technology or determine effective fruit infestation sampling protocols. Theoretically, traps to capture adult flies should aid growers in the timing of spray applications so that insecticides could be used more judiciously. Traps baited with apple cider vinegar or a combination of sugar-water and yeast are currently used to monitor adult D. suzukii flight patterns. However, without standard methods for trapping or management thresholds based on trap count data, it is questionable how much is gained by establishing and monitoring traps in crops. Establishing, monitoring, and maintaining traps is very labor intensive and the costs do not justify the benefits for many growers. Historically, trap data has not provided a reliable warning against D. suzukii attack, especially for susceptible crops in high-density population areas where considerable oviposition can occur in short time periods. Currently, no significant differences are found in any traps used for monitoring D. suzukii given differences between crops and environments where traps have been tested. Monitoring fruit infestation levels to guide management may also be impractical. It is unclear how many samples would be needed to accurately determine infestation levels. Furthermore, by the time larvae are detected in the fruit, it is too late for management action and damage has already occurred. No detailed studies could be found using monitoring for fruit infestation for this pest, and precision of sampling methodology is currently unavailable. Degree-day , or phenology models, are standard tools for integrated pest management in temperate regions and are used to predict the life stages of pests in order to time management activities and increase the effectiveness of control measures. Degree-day models work best for pests with a high level of synchronicity and few generations. Our data suggest that D. suzukii has short generation times, high reproductive levels, and high generational overlap compared to other dipteran fruit pests. Given this life history, stage-specific population models represent an alternative and potentially more applicable tool for modeling pest pressure. Pest population estimates may be greatly improved by employing additional tools such as mark recapture and analytical or individual-based models. The ability to describe and forecast damaging pest populations is highly advantageous for fruit producers, policy makers, and stakeholder groups. Many such studies have been directed at forecasting populations of medically important insect species. The major factors affecting survival, fecundity and population dynamics of drosophilids include temperature, humidity, and the availability of essential food resources. Therefore, an improved understanding of the role of temperature on D. suzukii may provide for a better understanding its seasonal population dynamics. In this paper, we present a population model for D. suzukii that represents a novel modification of the classic Leslie projection matrix, which has proven to be one of the most useful age structured population models in ecology, with applications for diverse organisms including plants, animals, and diseases. Our modification accounts for the effect of temperature on the survival and fertility of D. suzukii in calculating population growth of the organism. Typically, researchers have introduced elements of environmental stochasticity to matrix models to study environmental effects on population trajectories. However, our approach relies on temperature-dependent estimations of age specific fecundities and survival that are determined by models fit to life table data generated for multiple temperatures. Our environmentally dependent matrix model is unique in that it does not rely on simulation of environmental effects on populations, but the matrix itself is recalculated at each iteration in direct response to environmental input. Model predictions were run under environmental conditions from different regions to illustrate variation between and within study sites in different years. These simulations make important predictions about age structure and population trends that have implications for pest management both in a broad sense and with regional specificity.