You always wanted to know what pollinated rambutan, litchi, blueberries and all those other plants dependent on insect pollen movement? O yes, and also what is pollinating avocado?
Insect Pollination Of Cultivated Crop Plants
by S.E. McGregor, USDA
Originally published 1976
The First and Only Virtual Beekeeping Book Updated Continuously.
Additions listed by crop and date.
This book is out-of-print, but can be found on-line at ABE Books and then you can get the images that are missing from the online version of the book
This is an old book with a lot of old information, but a lot of it is still good. There is definitely more up-to-date information, but this is a good starting point. For avocado, another good source, or course is AvocadoSource which also has quite a number of articles on pollination of other tree species
Recently a group of UC Riverside researchers met to align themselves around the topic of pollination - The biology, effects, interactions of the various pollinator and pollinizers and how they are affected by our environment and how we might be able to manage them better. The participants in this pollination group have all manner of expertise and hopefully their interaction will bring a synergy of understanding to this very complicated subject.
IMAGE: Orbicules or "Ubisch bodies " (300 - 600nm granules), characteristics of Cupressaceae pollen, are visible on the surface of the exine (outer membrane). view more
Working in collaboration with teams from the Czech Republic and Japan, researchers from the Institut Pasteur, Assistance Publique - Hôpitaux de Paris (AP-HP), and Assistance Publique - Hôpitaux de Marseille (AP-HM) have identified, for the first time, the likely origin of the cross-reactivity between cypress pollen, peaches and citrus fruits. Their work has shown that these sources contain allergens belonging to a new family of proteins involved in pollen food associated syndrome. This discovery, which was published in JACI on August 3rd, paves the way for the development of novel allergy diagnostic tests.
Today, more and more people suffer from allergies, especially in industrialized countries (where almost 30% of the population is affected). In view of this, doctors are observing an increase in cases of "pollen food associated syndrome", or "combination" allergies, i.e. those which occur via a cross-reaction between pollen (respiratory allergies) and food (food allergies).
In Mediterranean regions, allergic reactions to cypress pollen/peach and cypress pollen/citrus fruits have been described in clinical practice. In such cases, certain people, having been exposed and sensitized to cypress pollen from a young age, go on to develop allergies to citrus fruits and peaches in adulthood. It is estimated that 60% of food allergies occur in combination with respiratory allergies.
Although several explanations had been put forward regarding the increase in these combination allergies, such as environmental or lifestyle changes, the structural basis for the cross-reaction between cypress pollen and certain fruits had, until now, not been formally identified.
A translational study (combining clinical observation and academic research), directed by researchers from the Institut Pasteur and AP-HP, working in partnership with teams from the Prague University of Chemistry and Technology (Czech Republic) and Hokkaido University (Japan), and also the Pneumo-Allergy Unit at La Timone Hospital in Marseille (AP-HM), has revealed for the first time the underlying physicochemical and immunological mechanisms behind this cross-reaction.
In this study, the scientists analyzed the physicochemical, immunological and structural properties of BP14, an allergen identified in cypress pollen. They were able to demonstrate numerous similarities with the peach allergen Pru p 7 and the orange allergen Cit s 7, both of which belong to the "snakin/GRP" (Gibberellin-regulated protein) protein family. These observations led the researchers to establish that BP14, Pru p 7 and Cit s 7 were members of a new family of respiratory and food allergens involved in pollen food associated syndrome.
As study coordinator Pascal Poncet (from the Institut Pasteur's Center for Innovation and Technological Research) explains: "a new concept has emerged - conditional sensitization. Once the immune system of an individual develops an intolerance to an allergen such as BP14, it is then more likely to become sensitive to similar allergens within the same protein family which are present in other allergen sources."
Demonstrating this cross-reactivity and identifying its causes could allow the new allergen family to be included in the battery of tests available to allergy sufferers, from which it is currently absent. As such, the discovery should contribute to improve allergy diagnosis, and lead to better patient treatment in keeping with the development of a personalized medicine.
Avocado trees can appear completely covered with flowers. A typical full grown healthy avocado tree in California can produce up to a million flowers a year, but, on the average, fewer than 200 flowers per tree will set fruit that will hold and develop to maturity and harvest (about 10,000 lbs/acre, or less). Upon occasion, we have seen some groves with trees setting an average of 500 flowers per tree (25,000 lbs/acre), but this is rare. More commonly, only 100 flowers (or less) per tree will set and hold fruit to maturity (5,000 lbs/acre or less), much to the distress of growers (Bender 2013). Flowering is typically spread over six to eight weeks.
The avocado flower has both functional male and female organs. The male floral organ, which produces pollen, is comprised of the anthers and stamens. The female floral organ is comprised of the stigma (which receives the pollen), style and the ovary. The flowers are small (10 mm diameter). The flowers are usually only open for 2–6 hours, then close and open again for 2–6 hours on the second day. When a flower opens for a second time, it produces pollen and the stigma is not receptive. Flowers then close and remain closed. Flowers will usually be one sex in the morning, closed in the middle of the day and the opposite sex in the afternoon. The timing of the sex phases can be quite defined, but environmental conditions will affect the timing and duration of the male and female phases. The mature tree can produce in excess of a million flowers during the flowering period.
Avocado cultivars are classified in two groups (A or B) based upon their flowering behavior. In the type ‘A' cultivars, the female organs are receptive to pollen in the morning and the pollen is released in the afternoon. Unfortunately, most of the currently available "B" varieties are classed as "greenskins", which return less to growers. In the type B'cultivars, the pollen is released in the morning, while the female organs are receptive in the afternoon. Type A cultivars include: Hass, Gwen, Lamb Hass, Pinkerton, Reed, Gem, and Harvest. Type B cultivars include: Bacon, Ettinger, Fuerte, Sharwill, Sir Prize, Walter Hole, Zutano, Marvel and Nobel. Both type. It is believed that the interplanting of complementary flower types can boost fruit set and therefore yield by making pollen available. The separation in time of the male and female phases has led most observers to believe that a vector or "pollinator" is needed to move pollen from one flower to another.
Steps to take to Improve Pollination (Bender 2014):
1. Bring beehives into the grove. The University of California farm advisors have usually recommended 1 – 2 strong hives per acre, but Ish-Am (2000) suggests that 1 hive is rarely sufficient, and in many cases 4 hives are required. California growers usually have to rent hives (in 2002 hive rentals averaged $42 per hive), but sometimes beekeepers will drop a load of 80 hives for free if the grower has good bee forage nearby. Bees should have water available; floating boards on ponds or reservoirs enables them to land and drink without drowning.
2. Add pollinizers to the grove. Ish-Am recommends a pollinizer tree row be located at least every fourth row. Some growers in California use pollinizers as wind-breaks around the grove, and some replace thinned-out trees with pollinizers.
3. Keep the orchard open. Direct sunlight should reach the lower branches of each tree in order for the trees to produce a “wall” of flowers down the ground. In avocado production, this can only be accomplished by pruning the upper branches on a yearly basis. Keeping open channels through the grove encourages the flight of bees.
4. Other types of bees? Bumblebees have been reported to increase yield in avocados in Israel where honeybee populations were low. New World Carniolan bees have been used in an experiment in San Diego County for pollination: results were inconclusive as to whether they increased yield compared to Italian honeybees, but it was found that they gather more nectar from avocado (Fetscher et al. 2000). Work with these bees, and other wild bees, may eventually reveal a more efficient pollinator for avocado.
Imagine going to the supermarket to stock up on groceries but coming home empty-handed because you just couldn't figure out how to work the shopping cart or figure out how to get to the ice cream tubs in the freezer aisle.
Welcome to the life of a bumblebee.
Gathering sweet nectar from flowers, it turns out, is much more difficult than one might think, and it requires a lengthy learning process. By the time a bee has figured out how to efficiently pry open the lips of a snapdragon flower, for example, most likely it has made dozens, if not hundreds, of floral visits.
How does a bee in charge of shopping for food needed to raise dozens of hungry larvae back in the hive learn to navigate the multitude of floral architectures it may encounter during an average workday, let alone over the course of its life?
Mostly by what biologists call associative learning, more widely known as trial and error, researchers have found. But while extensive research -- starting with famous bee researcher and Nobel laureate Karl von Frisch a century ago -- has focused on uncovering how bees forage for nectar, much less is known about how bees go about collecting pollen, which constitutes the most important protein source for the developing brood in the hive.
Avery Russell, Stephen Buchman and Daniel Papaj in the Department of Ecology and Evolutionary Biology at the University of Arizona decided to take a closer look. In a new paper published in the journal Behavioral Ecology, they tell a fascinating story of what is involved in a seemingly simple process of a bumblebee visiting a flower to gather pollen. And for the first time, they have untangled the subtle cues that a bee looks for when she visits a flower in search for pollen.
"For a long time, we have known that bees can learn all kinds of cues -- tactile, visual and olfactory -- when going after nectar rewards," says Russell, the study's first author. "When you open a can, you have to use a can opener, then use your fingers to pry the lid open. A bee might have to pop open the flower's petals, and might have to try many times over multiple trips until they get good at it. But not much was known in the context of pollen rewards."
Specifically, Russell and his co-authors wanted to know if bees need to learn in order to collect pollen efficiently from flowers that vary in their form. The research suggests they don't, and they don't need to.
"Our findings suggest that unlike nectar foraging, which requires complex learning behavior, bumblebees already know how to collect pollen," says Russell, who did the research as a doctoral student in the UA's Graduate Interdisciplinary Program in Entomology and Insect Science, "and they do it by switching between two responses that are seemingly hardwired into their brains."
Once a bumblebee touches down on a flower, it wastes no time. If it senses that the anthers are laden with abundant pollen just waiting to be shaken off like ripened apples from a tree, the bee does the obvious: a behavior that bee researchers call "scrabbling." Using its mandibles and legs, the bee brushes the pollen grains onto its body, then combs them off into collection baskets located on each of its hind legs.
"If you picture a happy toddler in a play pit filled with plastic balls, you get the idea of scrabbling," Russell says.
However, some flowers make their pollen grains more difficult to access, or sport intricate anther designs that dispense only a little bit of pollen at a time.
"That way, the plant makes sure pollinators don't eat it all, but carry it to other flowers for pollination instead, and also leave some for other visitors as well, so the flowers aren't limited to a single pollinator," he says.
When visiting some of these trickier flowers, Russell's team found, bumblebees switch to a different behavior called sonication -- or, in more familiar terms, buzzing. Not unlike a sonicating toothbrush that vibrates to shake plaque from teeth, a sonicating bee vibrates vigorously to free pollen grains hidden inside the flower.
The team observed that the bees switched between these two motor regimes depending on chemical and mechanical cues: They scrabbled when pollen was abundant, and sonicated when pollen was scarce, either because the flower already had been depleted or because its pollen is less accessible by design.
To tease apart the cues that trigger each behavior, the researchers made artificial flowers and treated some of them with chemical extracts from natural anthers. Bees visiting a surrogate flower without extract didn't stick around and took off again in search of more rewarding offerings. When they encountered a foam flower without pollen but with the chemical cue, they buzzed them in a futile attempt to harvest the nonexistent pollen. And when they sensed pollen grains, even artificial ones, scrabbling ensued.
"Bumblebees tend to sonicate on pollen-concealing anthers right away, but they also buzz accessible anthers when they can't detect pollen by touch," Russell says. "We think they do that in an effort to collect the dregs from a flower after most of its pollen has been harvested."
Being able to switch between two programmed routines allows bees to effectively collect pollen from flowers in many different shapes and forms, the researchers conclude. This flexibility also may explain a fact that had evolutionary biologists stumped for a long time: Flowers with concealed pollen stores evolved many times independently, suggesting that pollinators must always have had a way to harvest pollen from them, or else the co-evolution between the two would have led to a dead end and not survived.
"Researchers used to think that floral sonication is a behavior only used to collect pollen from concealed pollen stores," Russell says, "but because we often observe bees buzzing on flowers with accessible pollen, we conclude that it's a behavior that has evolved as a general strategy to collect pollen from any type of flower."
To buzz or to scrabble? To foraging bees, that's the question
Presenting bumblebees with various combinations of natural and artificial flowers laced with chemical and mechanical cues, UA biologists have discovered that for a bumblebee, foraging for pollen versus nectar is very different.
With hot, dry winds, the question came up this week about whether the hot temperatures or the low humidity would affect pollen viability. It turns out that both day and night time temperatures will affect pollen tube growth. That in ‘Hass' approximately 48 hours about 50 deg F is needed to complete pollen tube growth and fertilization. If temperatures drop at night to below 50, there's not enough time for fertilization to occur. As temperatures increase, fertilization occurs more easily. In the tropics, there can be high temperatures and high humidities and good fruit set. But this question was not about fertilization, but how long the pollen would remain viable at high temperatures and low humidities. Work was done Loupassaki and Vasilakis for the World Avocado Congress III Proceedings and they basically found that when humidity dropped below 40%, viability was very low. This last week we have seen humidities below 10%. It probably means that even with bee visitation, non-viable pollen is being delivered to the flowers. When humidities come back up, there will probably be good fertilization, as long as we have decent day and night time temperatures.
Many years ago Gary Bender, down in San Diego, went to the Gulf Region of the Middle East to help establish an avocado orchard. The trees flowered, but never set fruit.
University of California Cooperative Extension Ventura County 669 County Square Drive, Suite 100 Ventura, CA 93003 Phone: 805.645.1451 Fax: 805.645.1474
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