Avocado fruit set is lousy up and down the coast this year. The trees were flowering in many places from January to June. They kept trying to set fruit, but nada. According to Daniel Swain at UCLA Weather West, this was the coldest winter on record without freeze and a long drizzly spring with little sun - cool days and night time temperatures. Cold day time temps mean poor pollinator activity. Honeybees just weren't working much. Then if pollen is transferred to the female stage flower, it takes 48 hours of above 50 deg F for fertilization - the deposition of pollen on the stigma and growth of the pollen tube down the style to the ovule. If the temp at night drops below 50, the process stops and the ovule never gets fertilized. So it doesn't matter if day time is warm and the pollinators are working, if it gets cold at night, the fertilization process stops.
So that's exactly what happened. Cool days for poor pollination and then cold nights for fertilization. It didn't matter how hard the tree flowered, it just wasn't the right weather. It didn't matter if you sprayed gibberellic acid. The weather was just not right for fruit set this tear.
And this should set off alternate bearing for next year if we have the right weather conditions. So you might think seriously about pruning because there could be a branch breaking crop set next spring – if the weather is right.
Interestingly,just as an observation it looks like GEM and Lamb Hass right next to Hass did set fruit just at the end of the flowering period. So there is some difference in varieties to weather conditions.
Image from American Museum of Natural History
The cool/moist weather has also created conditions for anthracnose and alternaria in fruit which causes problems for the consumer, but also caused early fruit drop and color change in the fruit on the tree. The trees just can't hold on to the fruit as one normally expects. It's a tough year for avocado growers. In the Central Valley all the stone fruit is late by almost a month. Apricots and cherries are just coming in season when they should have been available in late May.
Weird and Maybe we are going to have to get used to it.
pollination - movement of male pollen to female stigma
fertilization - growth of pollen tube down to stimulate ovule
Microbes multiply in heat,
Bumblebees pollinate many of our favorite foods, but their own diet is being upset by climate change, according to a new UC Riverside study.
Bombus impatiens, aka the common eastern bumblebee, served as taste tester for this experiment.
There's a sweet spot where floral nectar that bees eat has just the right balance of microbes like bacteria and yeast in it. Hotter weather can upset the balance, endangering the bees' health and potentially, our own.
A new study in the journal Microbial Ecology examines the effects of these nectar composition changes on an American bumblebee. Without bumblebees, who perform a type of pollination that honeybees do not, it would be difficult to mass produce food crops like tomatoes, blueberries, peppers, or potatoes.
“Micro changes in floral nectar may alter the way bees forage and look for food, affecting their health and in turn, potentially affecting human health, by reducing the availability of fresh foods,” said UCR entomologist and study lead Kaleigh Russell.
Bumblebees do enjoy nectar with some microbes in it, but too much of a good thing can deter them, Russell said.
With even a small increase in temperature, microbes' metabolism speeds up, causing them to reproduce more and eat up a higher percentage of the sugars in the nectar. “Less sugar means the nectar could be less palatable for our pollinators,” Russell said.
To test the bumblebees' taste preferences, Russell made nectar in a laboratory. Some was sterile and some contained microbes, and she grew both at a lower and a higher temperature.
The lower temperature, 80.6 degrees Fahrenheit, represents the average springtime high for Riverside in 2017. The higher temperature, 89.6 F, corresponds with what the predicted average temperature will be at the end of the century due to climate change.
Nectar from wild mustard, abundant in Southern California, was collected for this experimental taste test.
A clear preference for some level of microbes was evident even when the nectar contained less sugar. However, the bees only went for this less sugary nectar containing a moderate amount of microbes at the cooler temperature. They did not prefer the nectar with too many microbes, as well as the nectar with no microbes at all.
It isn't yet clear why the bees have such specific preferences. Russell speculates that bacteria or yeast may help bees digest sugars in the nectar. Another theory is that the microbes produce secondary metabolites that aid in bee health.
What is clear is that it isn't likely that an increase in average temperatures will have a positive effect on bumblebees.
“We could see shifts in the locations of bee communities, since they leave when they can't find the food they like or need,” Russell said. “We might also see a decline in overall pollinator populations.”
For concerned readers with gardens, Russell recommends growing native plants that have not been treated with insecticide. “That's the best thing someone could do right now to help bumblebees,” she said.
Rae Olsson firstname.lastname@example.org 509-335-4846
PULLMAN, Wash. - A tiny bee imposter, the syrphid fly, may be a big help to some gardens and farms, new research from Washington State University shows.
An observational study in Western Washington found that out of more than 2,400 pollinator visits to flowers at urban and rural farms about 35% of were made by flies--most of which were the black-and-yellow-striped syrphid flies, also called hover flies. For a few plants, including peas, kale and lilies, flies were the only pollinators observed. Overall, bees were still the most common, accounting for about 61% of floral visits, but the rest were made by other insects and spiders.
"We found that there really were a dramatic number of pollinators visiting flowers that were not bees," said Rae Olsson, a WSU post-doctoral fellow and lead author of the study published in Food Webs. "The majority of the non-bee pollinators were flies, and most of those were syrphid flies which is a group that commonly mimics bees."
Syrphid flies' bee-like colors probably help them avoid predators who are afraid of getting stung, but they are true flies with two wings as opposed to bees which have four. The flies might have additional benefits for plants, Olsson added, since as juveniles they eat pests like aphids. As adults, they consume nectar and visit flowers so have the potential to move pollen the same way that bees do, though it is less intentional than bees who collect pollen to feed their young.
For the study, the researchers surveyed plants and pollinating insects and spiders on 19 rural farms and 17 urban farms and gardens along the Interstate 5 corridor in Western Washington. They conducted surveys six separate times over two years. In addition to the visits by bees and syrphid flies, they also catalogued more rare visits by other arthropods including wasps, lacewings, spiders, butterflies, dragonflies, beetles and ants--all with visits of less than 4%.
Olsson first noticed the many different non-bee pollinators while working on a bee-survey project led by Elias Bloom, a recent WSU doctoral graduate. The results of this study underscore the need for researchers as well as gardeners and farmers to pay more attention to alternative pollinators, Olsson said, and hoped that similar studies would be conducted in other regions of the country.
"Bee populations are declining, and we are trying to help them, but there's room at the table for all the pollinators," Olsson said. "There are a lot of conservation and monitoring efforts for bees, but that doesn't extend to some of the other pollinators. I think people will be surprised to find that there are a lot more different types of pollinating insects - all we really need to do is to start paying a little more attention to them."
The study also noted pollinator differences between rural and urban spaces. Observations sites in urban areas showed a greater diversity of pollinators corresponding with the wider range of plants grown in city gardens and smaller-sized farms. Rural farms with their larger fields of plants had a greater abundance.
For every grower, urban or rural, who is interested in increasing the number and diversity of pollinators visiting their fields or gardens, Olsson recommended increasing the variety of flowering plants.
Making sure that something is flowering all throughout the season, even if on the edge of a field, will support the biodiversity of pollinators because their different life stages happen at different times of the year.
"Some pollinators like certain butterflies and moths are only present in a pollinating form for a small period of time," Olsson said. "They may only live for a few days as adults, so when they emerge and are ready to pollinate, it's good to make sure that you have something for them to eat."
Photo: Not a bee, a hover fly or syrphid fly
A recent publication points out the need for identifying and improving habitat for avocado pollinators.
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.
Read the full article: https://onlinelibrary.wiley.com/doi/full/10.1111/jen.12869
Hover fly visiting an avocado flower in the South-West of Western Australia (©2021 DPIRD)
- Author: Brittney Goodrich
By Brittney Goodrich, Assistant Cooperative Extension Specialist, Agricultural and Resource Economics, University of California, Davis
If you own or manage a commercial avocado orchard, you have likely debated at one point or another whether to seek out honey bee colonies to pollinate your orchard, and how much to pay the beekeeper for those pollination services. A recent academic paper published in the Journal of Applied Entomology summarizes findings regarding the role of insect pollination in avocado production, and I would encourage you to take a look, especially if you have not sought out honey bee colonies in the past (see Dymond et al., 2021 referenced at end of article). Dymond et al. conclude that “In 19 out of 23 studies, insect pollinators contributed significantly to pollination, fruit set and yield.” And “In most situations, growers will benefit from an increased density of pollinators.” However, they note that renting honey bee colonies may not make economic sense for every orchard. In this article, I'll touch on some factors that may influence a grower's decision to place honey bee colonies in avocado orchards for pollination services.
Are managed honey bee colonies needed in your orchard?
Given the conclusions of Dymond et al. (2021), if you are a grower who has not placed honey bee colonies in your avocado orchard in the past, this may be something to consider going forward. Though, doing so may not guarantee increases in yield because your orchard has likely been receiving pollination services from wild pollinators and/or honey bee colonies located nearby. If your orchard is located near natural pollinator habitat, you may receive sufficient wild pollinators to obtain significant fruit set, in which case additional bees may not be necessary. Foraging honey bees typically seek out the least competitive forage sources, so if your orchard without honey bee colonies is located near an orchard in which the grower paid for pollination services, it is likely you are “borrowing” bees from your neighbor's orchard. In that situation, bringing in managed honey bees may not make the most economic sense from your perspective, but it may make your neighbor happy!
Supply of honey bee colonies
Depending on location, avocado bloom can begin in late March/early April and last through May/June (Bender, 2013). One important factor in the availability of honey bee colonies for pollination services for avocado bloom is the number of colonies in California at the end of almond bloom. In 2020, roughly 2.4 million colonies were required to pollinate California's almond orchards, far exceeding the number of colonies that remain in California year-round. This means roughly 2 million colonies were shipped in to California to meet this demand. This number makes up approximately 88% of the total number of colonies in the U.S., so beekeepers bring colonies from as far as New York and Florida to meet these needs (Goodrich and Durant, 2020; Goodrich, 2019).
For avocado growers, this means at the very beginning of avocado bloom, there may still be a surplus of bees left in California. Beekeepers from northern states, e.g., North Dakota, South Dakota, and Montana, can't transport colonies back right away given there may still be snow on the ground and little blooming for the bees to forage on. However, as spring progresses throughout the rest of the U.S., the number of bees in California begins to decrease substantially. Looking at the U.S. Department of Agriculture (USDA) Honey Bee Colonies Report, on April 1, 2018, there were 1.1 million colonies in California and by July 1, 2018 the number of colonies was nearly half that at 590,000.
Traditionally, California beekeepers would place colonies in or near citrus orchards for honey production after almond bloom (Champetier, 2010). In addition to being good for bees (and their keepers), this practice has benefitted growers of nearby crops that require pollination services. For example, a beekeeper might place colonies for no charge in an avocado orchard that needs pollination services simply to gain access to the prime honey-producing location. However, given the surplus of colonies remaining in California after almond bloom, I suspect (notably without any direct empirical evidence) these locations are not as prime as they once were. Supporting evidence for my theory is shown in Figures 1 and 2. Figure 1 displays a fairly prominent downward trend in total honey-producing colonies in California since 1990, and over the same time period, the average amount of honey produced per colony in California has trended downward as well. If the essential inputs to honey production, i.e., floral nectar and pollen sources, were roughly equivalent over this time period, one would expect for honey production per colony to increase as the number of colonies decreases given the lower competition over floral sources. Figure 2 shows bearing citrus acreage over this time period. Citrus acreage has decreased since the late 1990s, which might partially explain lower honey production per colony in recent years. However, the decreasing trend in honey production per colony occurred even in the late 1990s when citrus acreage in California was increasing. These trends suggest that the influx of bee colonies due to almond pollination requirements have encroached on forage resources previously utilized by California beekeepers, lowering their potential for honey production. Again, I caveat the previous suggestion with the fact that I have not yet directly tested this hypothesis, so these relationships could be coincidental.
Get the whole story at: http://ceventura.ucanr.edu/Com_Ag/Subtropical/