Ohad Afik

Wild Pollinators Enhance Fruit Set of Crops Regardless of Honey Bee Abundance

Honeybees Cant Do It Alone The majority of food crops require pollination to set fruit with the honeybee providing a pollination workhorse, with both feral and managed populations an integral component of crop management (see the Perspective by Tylianakis, published online 28 February). Garibaldi et al. (p. 1608, published online 28 February) now show that wild pollinators are also a vital part of our crop systems. In more than 40 important crops grown worldwide, wild pollinators improved pollination efficiency, increasing fruit set by twice that facilitated by honeybees. Burkle et al. (p. 1611, published online 28 February) took advantage of one of the most thorough and oldest data sets available on plant-pollinator interaction networks and recollected data on plant-pollinator interactions after more than 120 years of climate change and landscape alteration. The historical data set consists of observations collected by Charles Robertson near Carlinville, Illinois (USA), in the late 1800s on the phenology of plants and their pollinating insects, as well as information about which plants and pollinators interacted with one another. Many sites were revisited in the early 1970s and in 2009 and 2010 to collect similar plant-pollinator data. Pollinator function has declined through time, with bees showing lower visitation rates and lower fidelity to individual plant species. Flower visits by wild insects enhanced fruit production in crops worldwide, well beyond the effect of bees. [Also see Perspective by Tylianakis] The diversity and abundance of wild insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. We found universally positive associations of fruit set with flower visitation by wild insects in 41 crop systems worldwide. In contrast, fruit set increased significantly with flower visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Visitation by wild insects and honey bees promoted fruit set independently, so pollination by managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild insect assemblages will enhance global crop yields.

Analyses of avocado (Persea americana) nectar properties and their perception by honey bees (Apis mellifera).

Honey bees are important avocado pollinators. However, due to the low attractiveness of flowers, pollination is often inadequate. Previous work has revealed that avocado honey is relatively unattractive to honey bees when compared with honey from competing flowers. We characterized avocado honey and nectar with respect to their odor, color, and composition of sugars, phenolic compounds, and minerals. Furthermore, we tested how honey bees perceive these parameters, using the proboscis extension response bioassay and preference experiments with free-flying bees. Naïve bees were indifferent to odors of avocado and citrus flowers and honey. Experienced bees, which were collected in the field during the blooming season, responded preferentially to odor of citrus flowers. The unique sugar composition of avocado nectar, which contains almost exclusively sucrose and a low concentration of the rare carbohydrate perseitol, and the dark brown color of avocado honey, had no negative effects on its attractiveness to the bees. Phenolic compounds extracted from avocado honey were attractive to bees and adding them to a solution of sucrose increased its attractiveness. Compared with citrus nectar and nonavocado honey, avocado nectar and honey were rich in a wide range of minerals, including potassium, phosphorus, magnesium, sulfur, iron, and copper. Potassium and phosphorus, the two major minerals, both had a repellent effect on the bees. Possible explanations for the presence of repellent components in avocado nectar are discussed.

Honeybee, Apis mellifera, round dance is influenced by trace components of floral nectar

The round dance and mutual feeding (trophallaxis) enable honeybees to transfer information concerning a food source, including its profitability. For nectar, which consists mainly of sugars, profitability is usually defined by its energetic value. Nectars, however, also contain a wide range of trace components, some of which affect their attractiveness. Honeybees produce honey from nectar. We compared the round dance and trophallaxis behaviours of bees foraging on avocado and citrus honey solutions, as a substitute for nectars. These sources differ in their trace-elements composition, with avocado nectar and honey containing higher concentrations of minerals than citrus nectar and honey. In a second experiment, we compared the behaviour of bees foraging on sucrose solution and sucrose solution enriched with four major mineral components of avocado nectar. Subjects foraging on avocado honey had a significantly lower probability of dancing than those foraging on citrus honey, a rate of direction reversals that was almost one half, a lower total number of reversals, shorter dance duration and longer trophallaxis time. When avocado honey was supplied to bees that previously fed on citrus honey, most of them avoided it, indicating a strong context effect. When foraging on mineral-enriched sugar solution, dance variables tended to be lower compared with sucrose solution without minerals, but differences were smaller than the differences between the honey solutions. These results show that nectar trace components affect the estimation of nectar profitability by bees and consequently recruitment of new foragers to nectar sources.

Watermelon pollinators exhibit complementarity in both visitation rate and single-visit pollination efficiency

Summary 1. The concept of pollinator niche complementarity maintains that species-rich pollinator communities can provide higher and more stable pollination services than species-poor communities, due to contrasting spatial and/or temporal pollination activity among groups of pollinators. Complementarity has usually been examined in pollinators’ patterns of flower visitation or abundance, while largely neglecting the possibility of complementarity in patterns of single-visit contribution to fruit/seed set (pollination efficiency). However, variability in pollination efficiency can greatly affect pollinators’ overall pollination services and may therefore contribute an additional, important aspect of complementarity. 2. In this study, we investigated the existence of pollinator complementarity in both visitation rates and pollination efficiencies. The study was conducted in 43 watermelon fields cultivated for seed consumption in a Mediterranean agro-natural landscape in central Israel. We studied spatiotemporal variation in pollinators’ visitation activity, measured by repeated observations and netting, and single-visit pollination efficiency, measured by the fruit and seed set rates of hermaphrodite flowers exposed to a single bee visit. Visitation and pollination efficiency were measured throughout the day and season, within and between fields with contrasting availability of nearby wild plants, and among flowers of different sizes. 3. Pollinator species’ visitation rates as well as single-visit fruit set efficiencies, but not seed set efficiencies, exhibited significant spatiotemporal variation that contributed to their complementarity. Pollinators’ visit frequencies were affected by surrounding land use, location within field, time throughout the season, and time of day. Pollinators’ fruit set efficiencies were affected by ovary size and time of day. 4. Synthesis and applications. Crop pollinators may exhibit complementarity in both their visitation rates and pollination efficiencies, which can promote the overall level and stability of their pollination services. Complementarity in pollination efficiencies suggests further diversity effects on crop yield, and calls for taking into account the variability in pollination efficiency along spatiotemporal scales rather than considering it a constant, species-specific trait. However, some modes of niche complementarity may not necessarily translate into increased pollination services and crop yield; the relevance and limitations of such mechanisms should be considered in the light of the specific crop and management system studied.

Nectar Minerals as Regulators of Flower Visitation in Stingless Bees and Nectar Hoarding Wasps

Various nectar components have a repellent effect on flower visitors, and their adaptive advantages for the plant are not well understood. Persea americana (avocado) is an example of a plant that secretes nectar with repellent components. It was demonstrated that the mineral constituents of this nectar, mainly potassium and phosphate, are concentrated enough to repel honey bees, Apis mellifera, a pollinator often used for commercial avocado pollination. Honey bees, however, are not the natural pollinator of P. americana, a plant native to Central America. In order to understand the role of nectar minerals in plant—pollinator relationships, it is important to focus on the plant’s interactions with its natural pollinators. Two species of stingless bees and one species of social wasp, all native to the Yucatan Peninsula, Mexico, part of the natural range of P. americana, were tested for their sensitivity to sugar solutions enriched with potassium and phosphate, and compared with the sensitivity of honey bees. In choice tests between control and mineral-enriched solutions, all three native species were indifferent for mineral concentrations lower than those naturally occurring in P. americana nectar. Repellence was expressed at concentrations near or exceeding natural concentrations. The threshold point at which native pollinators showed repellence to increasing levels of minerals was higher than that detected for honey bees. The results do not support the hypothesis that high mineral content is attractive for native Hymenopteran pollinators; nevertheless, nectar mineral composition may still have a role in regulating flower visitors through different levels of repellency.

Inorganic nitrogen derived from foraging honey bees could have adaptive benefits for the plants they visit.

In most terrestrial ecosystems, nitrogen (N) is the most limiting nutrient for plant growth. Honey bees may help alleviate this limitation because their feces (frass) have high concentration of organic nitrogen that may decompose in soil and provide inorganic N to plants. However, information on soil N processes associated with bee frass is not available. The objectives of this work were to 1) estimate the amount of bee frass produced by a honey bee colony and 2) evaluate nitrogen mineralization and ammonia volatilization from bee frass when surface applied or incorporated into soil. Two cage studies were conducted to estimate the amount of frass produced by a 5000-bee colony, and three laboratory studies were carried out in which bee frass, surface-applied or incorporated into soil, was incubated at 25oC for 15 to 45 days. The average rate of bee frass production by a 5,000-bee colony was estimated at 2.27 to 2.69 g N month−1. Nitrogen mineralization from bee frass during 30 days released 20% of the organic N when bee frass was surface applied and 34% when frass was incorporated into the soil. Volatilized NH3 corresponded to 1% or less of total N. The potential amount of inorganic N released to the soil by a typical colony of 20,000 bees foraging in an area similar to that of the experimental cages (3.24 m2) was estimated at 0.62 to 0.74 g N m−2 month−1 which may be significant at a community scale in terms of soil microbial activity and plant growth. Thus, the deposition of available N by foraging bees could have adaptive benefits for the plants they visit, a collateral benefit deriving from the primary activity of pollination.

Selection and Breeding of Honey Bees for Higher or Lower Collection of Avocado Nectar

ABSTRACT Intensive activity of honey bees, Apis mellifera L., is essential for high fruit set in avocado, Persea americana Mill, orchards, but even when hives are located inside the orchard, many bees still search for alternative blooms. We tested for a possible genetic component for a preference of avocado bloom relative to competing bloom. The honey from each hive was extracted at the end of the avocado bloom and the concentration of perseitol, a carbohydrate that is unique to avocado, was analyzed as a measure for avocado foraging. During the first year, five bee strains were compared in three different sites in Israel. Significant differences were found between strains in honey perseitol concentrations, suggesting differences in their efficiency as avocado pollinators, although these differences were site dependent. At two sites, colonies with the highest and lowest perseitol concentrations were selected as parental “high” and “low” lines, Queens were raised from the selected colonies and were instrumentally inseminated by drones from other colonies of this line, During the second and third years, colonies with inseminated queens were introduced to the avocado orchards, together with the selected colonies still surviving from the previous year. Colonies of the high line had greater perseitol concentrations than those of the low line, Selected colonies that survived from the previous year performed consistently vis-à-vis perseitol concentration, in the second year of testing. Heritability value of 0.22 was estimated based on regression of offspring on midparent. The results reveal a heritable component for willingness of honey bees to collect avocado nectar.

Honeybee Pollination Affects Fruit Characteristics of Sweet Pepper Grown Under Net-Houses

Abstract In modern agriculture, many high-value cash crops that were formerly cultivated in open fields are now grown in greenhouses and net-houses. While changing the cultivation environment, attention is needed to ensure adequate pollen transfer to the stigma due to absence of wind, isolation from wild pollinators and low viability of reproductive organs due to the extreme temperature under those conditions. This study explores the effects of honeybee (Apis mellifera L.) pollination on various fruit characteristics of several different cultivars of sweet pepper (Capsicum annuum L.) under enclosed conditions. In all 16 cultivars examined during two growing seasons, bee pollination increased numbers of seeds per fruit, and had a significantly positive effect on fruit placenta weight, fruit weight, fruit width and fruit-wall thickness. While fruit diameter consistently correlated with bee pollination, fruit-length response alternated between seasons. It may be concluded that although bee pollination is a powerful tool for affecting fruit characteristics in sweet pepper, each cultivar exhibits different levels of response. Cultivars need to be evaluated separately, relative to market demand, when considering the use of bees for pollination.

Revisiting powdered sugar for varroa control on honey bees (Apis mellifera L.)

Prior to our study, when an experiment required Varroa free colonies, we would dust bees with powder sugar as a means of removing mites. Dusting with powder sugar was also gaining popularity in the beekeeping arena as a method of controlling Varroa. In 2009, researchers in Florida conducted a study which examined the effi cacy of powder sugar and found it did not help in controlling Varroa. However, even though the study was sound, powder sugar only dislodges phoretic mites and not ones inside the cell. Therefore, for powder sugar to be effective it would have to be applied during broodless periods, which Florida rarely experiences due to its warmer climate. So we decided to design an experiment that would test the effi cacy of powdered sugar when applied during broodless times verses when brood was present. Unfortunately, as the study revealed, relying solely on powdered sugar as a means of controlling Varroa mites does not keep mite populations from reaching devastating levels. This was bad news for us here at the lab. We were hoping that powdered sugar would be the cure-all, a silver bullet, that one control method that worked which didn’t include chemicals in the mix, but it’s not. Yes, it does work at dislodging mites but is not “powerful” enough to remove enough mites in order to keep them from eventually causing damage to colonies. If you are or are planning to use powder sugar, be aware that it needs to be “part of” your Varroa management scheme and not your only choice. Below then is the paper we published showing the results of our study. It was originally published in the Journal Of Apicultural Research, an IBRA publication www.IBRA.org. We thank them for permission to reprint this important study on these pages.

The components that determine honeybee ( Apis mellifera) preference between Israeli unifloral honeys and the implications for nectar attractiveness

Unifloral honeys are honeys that are dominated by a single nectar source. Several samples of Israeli honeys were analyzed for their physicochemical characteristics and tested by pollen analysis for their botanical source. Based on pollen content, unifloral honeys were harvested only from landscapes of planted forests including: aethel (Tamarix sp.), carob (Ceratoniasiliqua), and eucalyptus (Eucalyptus sp.). However, honeys extracted from agricultural landscapes should also be considered as unifloral due to pollen underrepresentation. No evidence for unifloral honeys from natural landscapes was found. Later, honeybee preference between different honeys and sucrose solution was tested and these preferences were correlated with honey traits. The preference experiment revealed that bees tend to prefer sucrose solution rather than any honey source. Among honeys, bees showed the highest preference for citrus honey and the lowest preference for avocado honey. Preference for aethel, cotton, and eucalyptus was intermediate. The electrical conductivity value of the honeys was negatively correlated with honey preference, indicating that the mineral content of honey, and probably of nectar, affects the attractiveness to bees.