Native flower strips increase visitation by non-bee insects to avocado flowers and promote yield

Pollination is an essential ecosystem service for pollinator-dependent crops and plant communities. Apis mellifera L. is by far the most commonly used species to obtain this service in agriculture. However, there is growing evidence of the importance for crop yields of the service provided by wild bees and non-bee insect pollinators. Establishing flower resources in agricultural landscapes is a management practice that can increase insect pollinator populations and improve crop yields. We established perennial native flower strips (NFS) in four avocado orchards in central Chile during autumn 2017. We monitored flower visitors and counted newly formed fruits in avocados near and far from NFS in spring 2019, to assess flower visitor groups, flower visitation rates and fruit numbers. Only A. mellifera visited avocado flowers within bees, whereas both the managed A. mellifera and wild bees were the main visitors to the NFS. NFS increased visitation rates to adjacent avocado of flies, and with a trend for the sum of all non-managed flower visitors (i.e. excluding A. mellifera). However, there were no differences in the rates of A. mellifera visitation to avocados near and far from NFS. Avocado fruit numbers were higher among avocados near NFS than among those farther away. This difference could be due to better pollination by the increased visits to avocado flowers by flies or other wild insects. Therefore, NFS could contribute to crop fruit number, as well as conservation of native flora, wild bees and non-bee pollinators on fruit farms in the “Central Chile” biodiversity hotspot.     

Pollination Services Provided by Bees in Pumpkin Fields Supplemented with Either Apis mellifera or Bombus impatiens or Not Supplemented

Pollinators provide an important service in many crops. Managed honey bees (Apis mellifera L.) are used to supplement pollination services provided by wild bees with the assumption that they will enhance pollination, fruit set and crop yield beyond the levels provided by the wild bees. Recent declines in managed honey bee populations have stimulated interest in finding alternative managed pollinators to service crops. In the eastern U.S., managed hives of the native common eastern bumble bee (Bombus impatiens Cresson) may be an excellent choice. To examine this issue, a comprehensive 2-yr study was conducted to compare fruit yield and bee visits to flowers in pumpkin (Cucurbita pepo L.) fields that were either supplemented with A. mellifera hives, B. impatiens hives or were not supplemented. We compared pumpkin yield, A. mellifera flower visitation frequency and B. impatiens flower visitation frequency between treatments. Results indicated that supplementing pumpkin fields with either A. mellifera or B. impatiens hives did not increase their visitation to pumpkin flowers or fruit yield compared with those that were not supplemented. Next, the relationship between frequency of pumpkin flower visitation by the most prominent bee species (Peponapis pruinosa (Say), B. impatiens and A. mellifera) and fruit yield was determined across all pumpkin fields sampled. Fruit yield increased as the frequency of flower visits by A. mellifera and B. impatiens increased in 2011 and 2012, respectively. These results suggest that supplementation with managed bees may not improve pumpkin production and that A. mellifera and B. impatiens are important pollinators of pumpkin in our system.     

The role of insect pollinators in avocado production: A global review

Insect pollination increases the yield and quality of many crops and therefore, understanding the role of insect pollinators in crop production is necessary to sustainably increase yields. Avocado Persea americana benefits from insect pollination, however, a better understanding of the role of pollinators and their contribution to the production of this globally important crop is needed. In this study, we carried out a systematic literature review and meta-analysis of studies investigating the pollination ecology of avocado to answer the following questions: (a) Are there any research gaps in terms of geographic location or scientific focus? (b) What is the effect of insect pollinators on avocado pollination and production? (c) Which pollinators are the most abundant and effective and how does this vary across location? (d) How can insect pollination be improved for higher yields? (e) What are the current evidence gaps and what should be the focus of future research? Research from many regions of the globe has been published, however, results showed that there is limited information from key avocado producing countries such as Mexico and the Dominican Republic. In most studies, insects were shown to contribute greatly to pollination, fruit set and yield. Honeybees Apis mellifera were important pollinators in many regions due to their efficiency and high abundance, however, many wild pollinators also visited avocado flowers and were the most frequent visitors in over 50% of studies. This study also highlighted the effectiveness of stingless bees (Meliponini) and blow flies (Calliphoridae) as avocado pollinators although, for the majority of flower visitors, there is a lack of data on pollinator efficiency. For optimal yields, growers should ensure a sufficient abundance of pollinators in their orchards either through increasing honeybee hive density or, for a more sustainable approach, by managing wild pollinators through practices that protect or promote natural habitat.     

Managed Bumblebees Outperform Honeybees in Increasing Peach Fruit Set in China: Different Limiting Processes with Different Pollinators

Peach Prunus persica (L.) Batsch is self-compatible and largely self-fertile, but under greenhouse conditions pollinators must be introduced to achieve good fruit set and quality. Because little work has been done to assess the effectiveness of different pollinators on peach trees under greenhouse conditions, we studied ‘Okubo’ peach in greenhouse tunnels near Beijing between 2012 and 2014. We measured pollen deposition, pollen-tube growth rates, ovary development, and initial fruit set after the flowers were visited by either of two managed pollinators: bumblebees, Bombus patagiatus Nylander, and honeybees, Apis mellifera L. The results show that B. patagiatus is more effective than A. mellifera as a pollinator of peach in greenhouses because of differences in two processes. First, B. patagiatus deposits more pollen grains on peach stigmas than A. mellifera, both during a single visit and during a whole day of open pollination. Second, there are differences in the fertilization performance of the pollen deposited. Half of the flowers visited by B. patagiatus are fertilized 9–11 days after bee visits, while for flowers visited by A. mellifera, half are fertilized 13–15 days after bee visits. Consequently, fruit development is also accelerated by bumblebees, showing that the different pollinators have not only different pollination efficiency, but also influence the subsequent time course of fertilization and fruit set. Flowers visited by B. patagiatus show faster ovary growth and ultimately these flowers produce more fruit. Our work shows that pollinators may influence fruit production beyond the amount of pollen delivered. We show that managed indigenous bumblebees significantly outperform introduced honeybees in increasing peach initial fruit set under greenhouse conditions.     

Low legitimate pollen flow in distylic Turnera hermannioides (Passifloraceae) and its consequences on fruit and seed set

Turnera hermannioides is a ruderal distylic subshrub, native to NE-Brazil. In the Catimbau National Park, situated within the semi-arid Caatinga region, we studied the pollination ecology of this species, emphasizing (1) effective pollinators; (2) characteristics of short- and long-styled flowers; (3) intra- and intermorph pollen flow; and (4) fruit and seed set. Short and long-styled morphs differ in pollen size and ornamentation, stigmatic surface, style and stamen length and nectar production. The flowers are obligate intermorphic outcrossers and depend on animals for pollination. The flowers of T. hermannioides attracted insect visitors of 25 species, among them butterflies, beetles, but mainly bees. Polylectic bees, such as Apis mellifera, stingless bees, and solitary Callonychium brasiliense were the most frequent visitors and the principal pollinators. The frequency of visits, however, was very low (on average 1.9 visits/flower/day), resulting in a low and unbalanced legitimate pollen flow, i.e. a much lower number of pollen grains from short-styled flowers reaching stigmas of long-styles than vice versa, which in turn compromised fruit and seed set. Surprisingly, Protomeliturga catimbaui and P. turnerae, both oligolectic on flowers of the Turneraceae-clade of the Passifloraceae s.l., were very rare flower visitors and did not contribute significantly to the pollination of Turnera hermannioides. We discuss how the low visitation rate and the inefficiency of pollinators (i.e. inefficiency in promoting legitimate pollination) compromise pollen flow and, consequently, fruit and seed set in this species.     

Status of pollinators and their efficiency in coffee fruit set in a fragmented landscape mosaic in South India

The region of Kodagu, South India, comprises a fragmented landscape with a high density of remnant forest patches dispersed within a mosaic dominated by shaded coffee agro-forests. We evaluated the role of self, wind and insect pollination to Coffea canephora production in this landscape. The giant Asian honeybee, Apis dorsata, which nests in remnant forests, was the main pollinator of coffee (accounting for 58% of the floral visitors). The proportion of flowers that developed into fruits was highest when hand cross-pollinated (44%), followed by open- (insect and wind combined; 33%) and wind- (22.1%) pollination treatments. Pollination by bees therefore increases fruit production by 50% over that achieved by wind. Self-pollination (1.7%) and no pollination (1%) treatments produced very low fruit set, emphasizing the importance of cross-pollination in C. canephora. Unlike measures of pollination success, initial fruit set (five weeks after flowering) proved an unreliable proxy for final fruit set. Size of adjoining forest fragments (mostly 0.3–20 ha, with a few exceeding 200 ha) positively influenced pollinator visitation to coffee flowers, but distance to such fragments had no influence on pollination. This study demonstrates the importance of cross-pollination for crop production in C. canephora, the important contribution that pollinating insects make to coffee production, and the benefits of relatively large forest fragments within the landscape mosaic to support insect pollinators of coffee. A comparison of pollinator composition to that of 100 years ago indicated that coffee pollination services remained intact despite changes in pollinator community composition.     

Mixed mating strategies and pollination by insects and wind in coconut palm (Cocos nucifera L. (Arecaceae)): importance in production and selection

Abstract 1 Coconut is one of the most important tropical crops. It is threatened by Lethal yellowing disease. Production and selection by breeding require pollination, yet little is known of the pollination requirements and breeding system of this palm. 2 This study was carried out from 1999 to 2001 in coconut plantations represented by five coconut ecotypes commonly found in Mexico. It is the first study in the Neotropics on pollination and the breeding system of this palm. 3 Hymenoptera were the most numerous and diverse visitors to coconut flowers. The greatest period of insect abundance occurred during the rainy season (July to October). Insect abundance on the flowers correlated highly and positively with precipitation. 4 The abundance of visitors to pistillate flowers did not vary with season but there were significant differences between palm ecotypes; the most insect‐visited flowers were of the Atlantic Tall ecotype. 5 The introduced honeybee (Apis mellifera) had the most appropriate foraging behaviour, visiting both pistillate and staminate flowers. These insects were probably the most efficient pollinators as they carry pollen on their ventral surface. Ants were present on flowers day and night but had no effect on pollination. 6 Pollination experiments indicated a mixed mating strategy: self‐pollination by geitenogamy produced almost 19% of the fruit set, but cross‐pollination (xenogamy) was the most important contribution (c. 30%). Anemophilous cross‐pollination only accounted for 10% of fruit set, whereas entomophily became the most important pollination mechanism under Yucatan conditions. 7 As coconut palm grows naturally on the oceanic strand in a wide variety of seasonal conditions of wind and rain, we suggest that they may have evolved pollination, breeding and mating systems that ensure fruit production under a wide variety of conditions, while maximizing the probability of cross‐pollination.     

Floral abortion and pollination in four species of tropical mangroves from northern Australia

We assessed natural rates of floral abortion in four common mangrove species from northern Australia and subsequently manipulated pollination experimentally. Sonneratia alba J. Smith exhibited the highest rate of fruit set of the four species (23%), indicating this mangrove was best able to utilise the natural pollination opportunities provided. Fruit set in S. alba appeared, however, to be pollinator limited, as large increases in fruit set occurred after manual cross-pollination of flowers. Avicennia marina (Forsk.) Vierh. had the highest rate of natural pollination, but fruit set was lower (15%) and appeared to be impeded by resource limitations. Although a range of insects visited Ceriops australis (C.T. White) Ballment, T.J. Sm & Stoddart, the rate of fruit set was low (3%) and the capacity for flower fertilisation limited, despite evidence of autogamy in this species. There was an indication of both resource and pollinator limitation in C. australis. Rhizophora stylosa Griff. exhibited limited fruit set (0.5%), possibly due to limiting maternal resources and the lack of adaptation of flowers to either animal or wind pollination. Large increases in fruit set were recorded after manual cross-pollination of R. stylosa flowers. R. stylosa and C. australis, characterised by resource rich propagules with long periods of development, both aborted a large proportion of propagules during the fruit maturation process.     

Key factors influencing forager distribution across macadamia orchards differ among species of managed bees

To achieve maximised and sustainable crop productivity, it is critical that we develop crop-specific strategies for managing pollination. Honey bees (Apis mellifera) and stingless bees (Tetragonula carbonaria) are considered effective pollinators of macadamia (Macadamia integrifolia). The introduction of managed honey bee or stingless bee hives into orchards is likely to boost the numbers of these insects visiting flowers; however, there is a lack of published information and consensus regarding their management for pollination. Here, we identify factors that affect the distribution of both honey bees and stingless bees across cultivated macadamia, and establish whether increased flower visitation leads to higher nut set. A gradient of bee visitation rates was created by placing colonies on the ends of a four-hectare block, and mixed-effect models were applied to assess forager abundance and nut set with respect to distance from hive, time of day, cultivar, and floral display size. Distance from colony had a strong effect on stingless bee numbers, with >96% of individuals recorded within 100 metres of colonies, whereas the distribution of honey bees was more closely related to daily floral display: trees with greater numbers of flowers attracted more honey bees. Simplified surveys conducted in a further 17 macadamia blocks confirm that these are broadly occurring distribution patterns. Bee abundance alone did not significantly predict nut production; however, an indirect effect of bee visits to flowers is inferred, as nut production increased with size of floral display. To encourage a more even distribution of bees and uniform pollination, we recommend placement of stingless bee hives to maximise their distribution through a block (e.g. at 100-m intervals) and management practices that promote even distributions of flowers across trees.     

Pollinator genetics and pollination: do honey bee colonies selected for pollen‐hoarding field better pollinators of cranberry Vaccinium macrocarpon?

1. Genetic polymorphisms of flowering plants can influence pollinator foraging but it is not known whether heritable foraging polymorphisms of pollinators influence their pollination efficacies. Honey bees Apis mellifera L. visit cranberry flowers for nectar but rarely for pollen when alternative preferred flowers grow nearby. 2. Cranberry flowers visited once by pollen‐foraging honey bees received four‐fold more stigmatic pollen than flowers visited by mere nectar‐foragers (excluding nectar thieves). Manual greenhouse pollinations with fixed numbers of pollen tetrads (0, 2, 4, 8, 16, 32) achieved maximal fruit set with just eight pollen tetrads. Pollen‐foraging honey bees yielded a calculated 63% more berries than equal numbers of non‐thieving nectar‐foragers, even though both classes of forager made stigmatic contact. 3. Colonies headed by queens of a pollen‐hoarding genotype fielded significantly more pollen‐foraging trips than standard commercial genotypes, as did hives fitted with permanently engaged pollen traps or colonies containing more larvae. Pollen‐hoarding colonies together brought back twice as many cranberry pollen loads as control colonies, which was marginally significant despite marked daily variation in the proportion of collected pollen that was cranberry. 4. Caloric supplementation of matched, paired colonies failed to enhance pollen foraging despite the meagre nectar yields of individual cranberry flowers. 5. Heritable behavioural polymorphisms of the honey bee, such as pollen‐hoarding, can enhance fruit and seed set by a floral host (e.g. cranberry), but only if more preferred pollen hosts are absent or rare. Otherwise, honey bees' broad polylecty, flight range, and daily idiosyncrasies in floral fidelity will obscure specific pollen‐foraging differences at a given floral host, even among paired colonies in a seemingly uniform agricultural setting.     

Relative contributions to seed production by floral visitors of slickspot peppergrass, Lepidium papilliferum (Brassicaceae)

Assessing the relative contributions to seed production made by different types of floral visitors is fundamental to understanding the evolution of floral morphology and the influence that particular pollinator taxa have on plant fitness and reproduction. This 3-year study examined the pollinator activity and the seed production in three populations of Lepidium papilliferum, a threatened mustard endemic to sagebrush-steppe habitat in southwest Idaho. Relative amounts of time visitor taxa spent foraging on flowers, visitation rates (number of flowers visited per unit time during a foraging bout), and pollination effectiveness (fruit set per single visit to a virgin flower) were recorded for each of 12 insect taxa that visited L. papilliferum flowers. Relative contributions to seed production were calculated as the product of relative interaction frequencies (the relative number of flowers visited by each taxon—the “quantity” component of pollination) and pollination effectiveness (fruit set per single visit to a virgin flower—the “quality” component of pollination). Despite the superiority of some insect taxa in terms of pollination effectiveness, estimates of relative pollinator contributions to seed production were influenced primarily by an insect taxon’s interaction frequency with flowers. Pollinator assemblages varied widely both spatially and temporally, which suggest that L. papilliferum is not under strong selective pressure to shift from its generalist pollination strategy toward greater specialization. For this threatened plant, reliance on a diverse assemblage of insect pollinators may serve as an important buffer against disruption in reproductive success caused by fluctuations in population sizes of individual pollinator taxa.     

Pollinator effectiveness and fruit set in common ivy, Hedera helix (Araliaceae)

Flowers of common ivy (Hedera helix L.) provide late season pollen and nectar for several insect groups, and its fruits are a winter and spring food source for frugivorous birds. Ivy benefits from insect pollination in order to set fruit, but it is unknown which flower-visiting insects are the most effective pollinators. Our observations suggest that Vespula wasps are potentially the most effective pollinators since they were frequent visitors, had relatively fast foraging rates, carried large numbers of pollen grains on their bodies and had the highest ‘Pollination potential PP index’ score (a measure of pollinator effectiveness) of all the insect groups examined. There was also a positive linear relationship between the proportion of ivy flowers that set fruit and wasp foraging activity in 0.5 m² quadrats. Visits by Vespula wasps may therefore be important for ensuring a supply of ivy fruits for birds.     

Effects of native pollinator communities on the physiological and chemical parameters of loquat tree (Eriobotrya japonica) under open field condition

Wild and managed pollinators are the key component of biodiversity, contributing to important ecosystem services such as pollination and supporting human food security. Pollination by insects is a crucial component of the food chain that ensures the production of fruits and strongly affects the fruit quality, but the effect of insect pollination on fruit physiological and chemical parameters is largely unknown. The current study was conducted to determine the insect pollinators diversity and their relative abundance in the loquat (Eriobotrya japonica) orchard during 2017–2019. Further, the effect of insect pollinators pollination on the physiological and chemical parameters of fruit quality as compared to control pollinated flowers was investigated. The results revealed that a total of 22 species from 3 families (Apidae, Halictidae, and Syrphidae) were identified during the flowering season. The Apidae and Syrphidae were the most frequently observed families with major groups honey bees (67.89%) and hoverflies (21.57%), respectively. Moreover, results indicated that the fruit yield by the open-pollinated flowers (22.31 ± 0.34 kg/tree) was significantly higher than the control pollinated flowers (14.80 ± 0.25 kg/tree). Physiological and chemical parameters of loquat fruit differed significantly when fruits obtained from open-pollinated flowers as compared to control pollinated flowers. These results suggested that native insect pollinators play important role in the fruit quality of loquat. Hence, maintenance of appropriate habitat of native pollinators near loquat orchards is necessary to ensure good productivity and fruit quality.     

Influence of brood, vent screening, and time of year on honey bee (Hymenoptera: Apidae) pollination and fruit quality of greenhouse tomatoes

Greenhouse tomatoes, Lycopersicon esculentum Miller (Solanaceae), are autogamous, but facilitated pollination results in increased fruit size and set. Previous research examining honey bee pollination in greenhouse tomato crops established that fruit quality resulting from honey bee visitation is often comparable to bumble bees (Bombus spp.) and significantly better than in flowers that receive no facilitated pollination. However, management alternatives have not been studied to improve tomato fruit quality when honey bees are the only pollination option available for the high-value greenhouse industry. We investigated whether the quantity of brood (eggs, larvae, and pupae) in a honey bee colony in the winter and screening on greenhouse vents in the summer would encourage honey bee foraging on tomato flowers. We also established the influence of time of year on the potential for honey bees to be effective pollinating agents. We constructed small honey bee colonies full of naive forager bees with either two frames of brood ("brood colonies") or two empty frames ("no-brood") and compared total fruit set and the number of tomato seeds resulting from fruit potentially visited by honey bees in each of these treatments to bagged flowers that received no facilitated pollination. There was no significant difference in the quality of fruit resulting from honey bees from "brood" and "no-brood" colonies. However, these fruits produced significantly more seeds than bagged flowers restricted from facilitated pollination. Honey bees from brood and no-brood colonies also resulted in 98% fruit set compared with 80% fruit set in bagged flowers that received no facilitated pollination. During the summer, the number of seeds per fruit did not differ significantly between unbagged flowers potentially visited by honey bees in screened greenhouses and unscreened greenhouses and bagged flowers that received no facilitated pollination. However, time of year did have a significant influence on the quality of fruit produced by honey bees compared with flowers that received no facilitated pollination, because no difference in seed number was observed between the treatments after mid-April. The results from this study demonstrate that the management of brood levels and vent screening cannot be used to improve the quality of fruit resulting from honey bee pollination and that honey bees can be a feasible greenhouse pollination alternative only during the winter.     

Pollen source and resource limitation to fruit production in the rare species Eremosparton songoricum (Fabaceae)

Eremosparton songoricum (Litv.) Vass. is a rare, central Asian desert species which shows lower fruit set and seed set (<16%) than most hermaphroditic species. We hypothesized that fruit production was limited by pollen and resources. To evaluate potential fruit abortion due to pollen limitation, supplemental hand‐pollination was undertaken, the mating system was investigated and the foraging behavior of pollinators was recorded. To investigate possibile resource limitation, flowers and young pods were artificially removed and fertilization were manipulated. The results showed that under natural pollination, the number of pollen deposited on the stigma greatly exceed the number of ovules per ovary. Mating system experiments showed that the species is self‐compatible, but depended on pollinators to set seeds. Supplemental outcross pollination increased fruit set significantly. The most frequent effective pollinator Megachile terminate Morawitz, was observed pollinating many flowers of the same individual plant (74.5±1.3%). These results suggested that fruit production is affected by insufficient outcross pollen rather than by pollen quantity. Removal of 2/3 of the flowers and young pods led to significantly higher fruit set, as did addition of fertilizers (N–P–K: 0.025–0.05–0.013 g, N–P–K: 0.05–0.1–0.025 g) showing that reducing resource acceptors and increasing inorganic resources both helps to improve fruit set. We therefore conclude that reproductive success of E. songoricum is limited by both outcross pollen and available nutrients.     

Pollination of invasive Eichhornia crassipes (Pontederiaceae) by the introduced honeybee (Apis mellifera L.) in South China

Heterostyly functions as an outcrossing mechanism facilitating accurate pollen transfer from anthers to stigmas of particular heights as a result of the behavior of specialist pollinators. However, heterostylous plants are also visited by generalist pollinators, which may affect the plant–pollinator mutualism. Eichhornia crassipes is a tristylous invasive species, with only the mid- and long-styled morphs (M and L) found in China. We recorded flower-visiting insects in Zhuhai, Zhongshan and Nanning in South China. We hand-pollinated the two morphs to determine their compatibility. In addition, by allowing controlled insect pollination in artificial isoplethically monomorphic and bimorphic populations, we undertook a detailed analysis of pollen deposition between the floral morphs, and fruit and seed set. Ranked by relative abundance, the flower-visiting insects were: Apis mellifera, A. cerana, Lasioglossum sp. and Eristalis arvorum. Hand pollination showed that both the M and L morphs were self-compatible, but the former was probably more so than the latter. Intra-morph pollen transfer by A. mellifera within a population was significantly greater than legitimate pollen transfer between populations, suggesting that the pollen exchange between populations was limited. Seed set of the L morph was significantly greater than that of the M morph in monomorphic populations, indicating intra-morph pollen deposition in the former was higher than in the latter. The results showed that A. mellifera was the major pollinator in South China and able to pollinate E. crassipes legitimately and to promote its fruit and seed set, even though high levels of intra-morph pollination occurred.     

Insect and wind pollination of an alpine biennial Aconitum gymnandrum (Ranunculaceae)

Wind pollination can provide reproductive insurance for animal‐pollinated dioecious plants in the absence of available pollinators, but combinations of insect and wind pollination (ambophily) have rarely been studied in hermaphrodite herbs. We examined the stable occurrence of insect pollination and wind pollination over 4 years in a population of a biennial Aconitum species (A. gymnandrum) with actinomorphic and degenerate sepals. The total frequency of visits of two bumblebee species showed no distinct fluctuations in the studied population among the 4 years. However, seed production of netted flowers after emasculation indicated wind pollination had occurred. The seed number of bagged flowers with one visit by bumblebees was significantly less than that of netted flowers after one visit, or in control flowers. Both seed number and fruit set of netted flowers were significantly lower than in control flowers. These results suggest that wind pollination provides supplementary pollen to unvisited and/or once‐visited flowers, but accounts for only a small amount of seed production compared to bumblebee pollination in natural conditions. Such a combination of insect and wind pollination might play an important role in maintaining sexual reproduction of this biennial herb, allowing it to persist in arid habitats on the Qinghai‐Tibetan Plateau, especially during Quaternary glacial periods when pollinator populations oscillated extensively.     

Pollination biology of fruit-bearing hedgerow plants and the role of flower-visiting insects in fruit-set

Background and Aims

In the UK, the flowers of fruit-bearing hedgerow plants provide a succession of pollen and nectar for flower-visiting insects for much of the year. The fruits of hedgerow plants are a source of winter food for frugivorous birds on farmland. It is unclear whether recent declines in pollinator populations are likely to threaten fruit-set and hence food supply for birds. The present study investigates the pollination biology of five common hedgerow plants: blackthorn (Prunus spinosa), hawthorn (Crataegus monogyna), dog rose (Rosa canina), bramble (Rubus fruticosus) and ivy (Hedera helix).

Methods

The requirement for insect pollination was investigated initially by excluding insects from flowers by using mesh bags and comparing immature and mature fruit-set with those of open-pollinated flowers. Those plants that showed a requirement for insect pollination were then tested to compare fruit-set under two additional pollination service scenarios: (1) reduced pollination, with insects excluded from flowers bagged for part of the flowering period, and (2) supplemental pollination, with flowers hand cross-pollinated to test for pollen limitation.

Key Results

The proportions of flowers setting fruit in blackthorn, hawthorn and ivy were significantly reduced when insects were excluded from flowers by using mesh bags, whereas fruit-set in bramble and dog rose were unaffected. Restricting the exposure of flowers to pollinators had no significant effect on fruit-set. However, blackthorn and hawthorn were found to be pollen-limited, suggesting that the pollination service was inadequate in the study area.

Conclusions

Ensuring strong populations of insect pollinators may be essential to guarantee a winter fruit supply for birds in UK hedgerows.Key words: Blackthorn, bramble, Crataegus monogyna, frugivorous birds, hawthorn, Hedera helix, hedgerows, ivy, insect pollination, Prunus spinosa, Rubus fruticosus, Rosa canina     

Pollinator Limitation and Crop Production: Experimental Observations on Few Economically Important Vegetable Crops in West Bengal,India

Pollination limitation and its impact on agricultural production is a serious concern of recent time. Assessment of the extent of dependency of various pollinator dependent crops on insect pollination assumes importance in this context. On the other hand, measures for restoring the pollination service needs to be explored for sustainable production of economically important crops particularly for the benefit of the small and marginal farmers. The present study aimed to assess the extent of insect pollinator dependency of brinjal (eggplant) fruit production and impact of honey bee (Apis cerana F) box introduction on the production in vegetable farms of North 24 Parganas, West Bengal, India. Through a pollinator exclusion experiment using enclosures it was found that brinjal fruit production reduces by 54.5 % when they are pollinator limited. This finding is in contrast with earlier report of 25 % dependency. The flower density in a pollinator limited environment was observed to increase by 31 %. This might be plant’s response to pollinator limitation where the plant invests more on reproductive structure than vegetative structures. However, this requires further exploration. Introduction of bee boxes in brinjal, pumpkin and pointed gourd farms showed significant increase in fruit production. This indicates both pollination limitation as well as the need for increasing the pollinators in the crop field for sustainable crop production.     

Petal herbivory by chrysomelid beetles (Phyllotreta sp.) is detrimental to pollination and seed production in Lepidium papilliferum (Brassicaceae)

Abstract.  1. Insect herbivory directed at flowers can decrease fruit and seed production by decreasing the attractiveness of a damaged flower to potential pollinators, by disrupting the transfer of pollen between pollinators and stigmas, or both.
2. Effects of petal herbivory by a chrysomelid beetle ( Phyllotreta sp.) on pollination and seed production in Lepidium papilliferum (Brassicaceae) were examined.
3. Under natural conditions, flowers with a hole chewed in a petal produced fruit and seed at a significantly lower rate than undamaged flowers (44% vs. 80% respectively). However, when damaged and undamaged flowers were hand pollinated, there was no significant difference in fruit or seed set (84% vs. 80% respectively).
4. Petal herbivory in L. papilliferum disrupts the effectiveness of insect-mediated pollination, but it does not physically inhibit pollination or seed production.