- Author: Ben Faber
Diadasia bituberculata – Digger Bee
The hills are alive with the sound of BEE-EEZZE. And often they are found crawling on the ground, as is the case of Digger Bees. At this time of year, they might be seen along the margins of avocado orchards, near hiking trails or in undisturbed areas of citrus orchards. They are called Digger Bees commonly, but this is just a generic name for a large group of bees that nest in the ground. There are many genera and species and because of the general lack of study of these bees they are lumped under the name Digger for lack of any greater knowledge and naming of them. In the case of this bee find reported here, they are possibly Diadasia bituberculata – as suggested by Robin Thorpe, retired UCD entomologist. They are uncommon in the rest of the world, but found here in California and western US.
There are several kinds of small hairy or metallic bees that dig into the soil to nest, hence the common name, digger bees. They are a diverse group that comes from different families and the term digger bee can include the andrenid bees, halictid bees, and colletid bees such as the plasterer and yellow-faced bees. These are solitary bees and native pollinators that are active early in the season. Each female digs a cylindrical underground tunnel as a nest where she reproduces (as opposed to social bees such as honey bees where only the queen reproduces and maintains a colony with the help of sterile workers). Although solitary, they form colonies that may have several hundred nests in one spot, but all nests are independently owned.
The subterranean nest is provisioned with a mixture of nectar and pollen collected from nearby flowering plants. This "bee-bread" is food for the bee's offspring (larvae) that develop in the underground chamber and emerge as adults the following year.
Digger bees are 1/4 to 1/2-inch-long and variable in color (mostly shiny metallic or dark, but some with markings of white, yellow or reddish brown). There is one generation of digger bees per summer and once the adults finish perpetuating the species by laying eggs of the next generation there will be no activity till the following spring.
Digger bee nests are commonly located in areas where grass and mulch are scarse, either from too much shade, previous drought conditions or other stress. Most of them like to fly around their airspace at different times of the day, something to do with mating, air temperature or staking territory. They often travel great distances to forage.
The threat of being stung by digger bees is unlikely. The bees are docile and not likely to sting unless handled or threatened. There is no nest guarding behavior or attack behavior like there is with social insects such as honey bees and yellowjacket wasps.
Image: Digger Bee "Colony", Thanks to Pest Control Adviser Jane Delahoyde's friend.
- Author: Ben Faber
The avocado is an odd duck in many ways and notably in its flowering. It has a complete flower, meaning it has both male and female parts in the same flower. Some plants have separate male and female flowers on the same plant and other species have male plants and female plants. The avocado, though acts – or is supposed to act – as if it had different stage flowers at different times. It opens as a female (stamens up), then closes and the same flower then opens as a male (stamens splayed out). They open separately in time, so, in theory, they cannot pollinate themselves – transfer pollen from the stamen (male part) to the pistil (female part). Fertilization occurs when the pollen tube grows down the stigma to the ovule and initiates a fruit – avocado sex. This is called synchronous (in a time sequence) dichogamy (split marriage). This is further complicated by having A and B flower types, where there are different lengths of time that the sexual stages are in flower. You can read more about it here:
http://ucavo.ucr.edu/Flowering/FloweringBasics.html
The problem is that the avocado hasn't read the text book about how it is supposed to flower and who or what transfers the pollen between the male and female stages. The flower can often open as a female and be that way for days and there won't be a single male flower around, or be in a male stage for days and no female. Or sometimes you find some females open and some males and sometimes that follow a time sequence where female may be open in one part of the day and males at another. If the varieties near each other are complementary (pollinizers), some having more females than male flowers and the other tree having more male flowers than females, there can be transfer of the pollen……. if the pollinator is around – a honeybee, native bee, hover fly, fly, wasp, thrips a myriad of potential agents. And if the weather right, and pollen is transferred to the female stage, it's possible there might be fertilization and fruit set.
So, the avocado is in full bloom through much of the avocado growing areas of California. And if you look out at the hives placed in the orchard you may not see any honeybees on the trees. Is that because they aren't flying? The weather is too cool? Because the flowers are in a male stage and they don't want pollen as a source of protein? Is there some other more attractive flower in the area? Do they no like the avocado nectar with its high sucrose and perseitol content?
What is going on? That is my question to you, dear readers? What are you seeing in your orchards? What insects are on the avocado flowers? What temperatures and time of the day are they flying? In what stage are the flowers, male or female? Are you seeing fruit set?
And while you are at it, what birds are you seeing in the orchard? How many different species? Typically there are hummingbirds nesting in avocados this time of year.
Go ahead and make your comments on line here.
Photo: Male and Female Stage Flowers
- Author: Ben Faber
We hear about the decline in honeybees (non-native, from Europe and the most commonly managed bees), but native bees are declining too and in many instances these are the pollinators of California avocado. The loss of any pollinators is a loss for agriculture as well as the environment. But here are the loss charts.
file:///C:/Users/Ben%20Faber/AppData/Local/Microsoft/Windows/INetCache/Content.Outlook/TL5O596C/Wild%20Bee%20Decline%20Threatens%20U%20S%20%20Crop%20Production.pdf
file:///C:/Users/Ben%20Faber/AppData/Local/Microsoft/Windows/INetCache/Content.Outlook/TL5O596C/Number%20of%20wild%20bees%20drops%20where%20theyre%20needed%20most-%20Science%20News.pdf
file:///C:/Users/Ben%20Faber/AppData/Local/Microsoft/Windows/INetCache/Content.Outlook/TL5O596C/Wild%20Bee%20Declines%20Threaten%20US%20Crop%20Pollination.pdf
file:///C:/Users/Ben%20Faber/AppData/Local/Microsoft/Windows/INetCache/Content.Outlook/TL5O596C/National%20Analysis%20of%20Wild%20Bee%20Abundance%20Highlights%20Areas%20of%20Concern.pdf
http://ucanr.edu/blogs/bugsquad/index.cfm?tagname=Claire%20Kremen
Next year will be better.
Bumblebee doing its thing
- Author: Ruben Alarcon
Pollination ecologists have typically studied a focal plant species and one or a few closely related pollinator taxa, such as bumblebees, which fostered the view that plant-pollinator relationships are highly specialized. However recent community-scale studies have revealed that many pollination systems are generalized, such that plants are visited by diverse, and spatiotemporally variable, pollinator assemblages. My goal is to reconcile traditional views of "specialized" floral adaptation with ecological generalization. Specifically my lab will be incorporating aspects of pollinator foraging behavior and flower/pollinator phenotype, into the analysis of plant-pollinator communities using network techniques. To address this issue my lab is exploring several plant-pollinator systems, including sub-alpine meadows in Colorado and California, the Sonoran Desert of southern Arizona, as well as the coastal sage scrub community surrounding the CSUCI campus.
From an applied perspective my lab is also working to maintain honeybee populations for crop pollination. In the United States over 130 crops require insect pollination, with nearly one-third of our diet coming from honeybee pollination services. However, over the last several years large numbers of honeybee colonies have been lost to Colony Collapse Disorder. Working with beekeepers and growers, my lab is trying to assess the benefits of providing supplemental forage for colonies transported to California every winter to pollinate almonds. We are also available to assist Ventura County beekeepers in identifying Nosema microsporidian infections and to monitor parasitic mites.
In addition to working with honeybees my lab also studies the nesting and foraging behavior of native bees, including the Blue Orchard Bee, Osmia lignaria. By furthering our understanding of native bee biology we hope to increase their use as sustainable pollinators. In collaboration with the UC Cooperative Extensions, Ventura County, we will also be studying how native bees could be used to improve avocado pollination.
- Author: Ben Faber
Dr. Gordon Frankie at UC Berkeley is teaming with me in Ventura County to jointly work on a pollination study for avocados. Dr. Frankie is studying how to increase native bee pollinators in avocado orchards. To do this, we plan on surveying the native bees that are in the area, identify the plants that they are foraging on and then plant those species in orchards to lure indigenous bees + pollinators in to the orchards. These plants will also be monitored for their attractiveness to beneficial insects which could control avocado thrips, persea mite along with other pests. We have applied for UC grants and will apply to CA Avocado Commission and CDFA Specialty Crops for money. We plan on planting the natives before the winter rains, if they ever come.
For a review of the native pollinators, check out the UC publication: How to attract and maintain pollinators in your garden. http://anrcatalog.ucdavis.edu/pdf/8498.pdf
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