Archive for the ‘Insect Updates’ Category

Wild Bee Pollinators: The Genus Andrena

Thursday, October 25th, 2012

By Sara Bushmann

In May and June of 2010 and 2011, I collected wild bees from 24 blueberry fields in Hancock County in the towns of Orland, Penobscot, Sedgwick and Blue Hill. By “wild” bees I mean any bee that is not a honeybee or a commercial bumblebee. Most of the wild bees are native, occurring naturally in Maine, but a few are not native and have been brought here by humans at some point in time. The wild bees are generally small- the size of a honeybee or less. The wild bees are mostly solitary, living individually or maybe in aggregations, but never forming the large colonies seen with honeybees. Naturally occurring bumblebees are wild, and they live in fairly large, social colonies, but I did not collect bumblebees. In the spring the only bumblebees that are out in the blueberry fields are the queens that are foraging for nectar and pollen before starting to lay eggs. If I collect a queen, I prevent the founding of an entire large colony of bumblebees. I did not want to do this, so I avoided collecting bumblebees whenever possible. 

I used two methods of capture. The first method involved placing small, colored cups filled with soapy water in the fields for 24-48 hours. This method catches anything attracted to the cup, including plenty of insects that are not bees (and unfortunately slugs like the cups as well). Many of the bees I’ve caught have come from these cup traps, but just because I catch a bee in a blueberry field doesn’t mean that that bee pollinates blueberry flowers. So, I also caught individual bees found foraging on blueberry flowers. From these bees I have made a list of possible wild bee blueberry pollinators.
A field assistant shows how to hand-catch bees on blueberry flowers

A field assistant shows how to hand-catch bees on blueberry flowers; taken in Addison ME, 2012.

This list includes 223 individual bees from 34 species caught on blueberry flowers. More than half of these 223 bees come from only three species:

Andrena carlini
Andrena vicina
Andrena carolina
The Andrena are ground-nesting bees. The adults dig a main burrow and create lateral burrows for the cells. They coat the walls of the cells with a waterproof lining to protect the eggs and larvae. In each cell they place a food mass (mostly pollen, but some nectar drops might be included) and one egg. The pollen is the food for the growing larva and sustains the bee until it reaches adulthood. Almost all Andrena overwinter in their cells as adults.  Most Andrena make individual nests and don’t share entrances with other adults.  They may place their nests near others. I have seen this in one blueberry field that had a southern-facing, sandy slope. Early in May when the blueberry flowers were just opening but no leaves were out, I came upon an aggregation of Andrena nests on this slope. 
Below is a bee at the entrance to a nest. It is not one of the three species listed above, but it is a similar size. The bee is about 3/4 an inch long and the hole not much more than 1/2 inch in diameter. This nest was located in a small, sandy bare patch in the middle of the blueberry field. 
These three species of Andrena might be quite important for blueberry pollination. In general, in 2011, in the fields where I caught the greater number of the Andrenid bees, the fruit set also was higher.
bee at the entrance to a nest

Bee at the entrance to a nest.

Bumblebee Disease and Diversity

Tuesday, September 18th, 2012

By Sara Bushmann, University of Maine

Welcome to the Pollinator Posts! 

On these web pages I’ll provide updates on some of the pollinator research projects being conducted in (mostly) Hancock and Washington Counties. Look for two more posts this year on or around Oct. 15 and Nov.15, and then again in April and May for updates on pollinator activity in the spring. 

(I gave a quick report of this study at the Blueberry Hill Farm Day gathering in July, 2012.) 
This project sprang out of concerns voiced by bee researchers throughout Europe and North America that some bumblebee species are declining. Some of the ideas as to why there are declines include habitat loss, pesticide exposure, and disease. But one suggestion particularly relevant to Maine blueberry agriculture is the idea that commercial bumblebees of the species Bombus impatiens (usually purchased in Maine from Koppert Biological Systems) are transmitting diseases to the wild bees. The suggestion is grounded on the concern that lab-reared bees could build up virulent strains of pathogens that they pass to other bees when they infect a shared resource such as a flower.
I decided to look at one pathogen, Nosema bombi, that infects bumblebees. This pathogen is of the group Microsporidia that are highly modified forms of fungi. In bees, these are parasites of the gut tract.
I asked these questions:
  1. What is the prevalence of Nosema bombi infections in wild bumblebees in Maine blueberry fields?
  2. Is the prevalence higher in areas where commercial bumblebees have been used?
Over two years I dissected 767 bumblebees caught in and around 25 blueberry fields. I found a total of 42 bees infected with Nosema, which means 5.47% of the wild bumblebees- a little less than six out of every 100- are infected. I looked at several factors that might explain why the infection occurred where it did. I looked at pruning methods, pesticide use or non-use, types of pesticides, field size, rotational stage (fruit-bearing year or not), and whether or not the field ever used commercial bumblebees for pollination.
None of these things offered an explanation for the occurrence of the disease.   According to other studies from other researchers, it is not out of the ordinary to see about 5% of the population infected with Nosema. So, based on my study, I cannot support the suggestion that commercial bumblebees have passed the disease agent Nosema to wild bumblebees. 


I did not find evidence of commercial bees transmitting Nosema to wild bumblebees. However, I did find that disease occurrence is not the same for the different species of bumblebees. One bumblebee that used to be common in Maine blueberry fields, Bombus terricola, is in serious decline throughout its range, which includes the northern US westward to the Plains. In a nationwide study this bee was associated with high levels of Nosema bombi.
In my study I caught 13 B. terricola in three years and 6 of these (almost half) were infected! Compared to all the other species of bees, that is a huge percentage of infected bees.
I knew that B. terricola used to be common in Maine fields.  So, I decided to see how bumblebee species in blueberry fields have changed over several years.  
Chart showing relative abundance of three bumblebee species

I found that B. terricola has greatly declined in abundance in blueberry fields, but that B. impatiens and B. ternarius have increased.  Bombus vagans has remained a common bumblebee in blueberry fields since the 60′s.  But, again, only B. terricola shows a high prevalence of Nosema infection. 
(The data from the 1990′s is provided by Frank Drummond, and the data from the 1960′s is from Boulanger et al. 1967, University of Maine Technical Bulletin No. 26 which is available online.) 
The increase of B. impatiens could mean that commercial colonies produce queens that overwinter and add to the wild populations.
I have found five other bumblebee species in blueberry fields, all of which occur in 10% or less of the population.
Bombus griseocolis
Bombus fervidus
Bombus borealis
Bombus perplexus
Bombus bimaculatus
For more information about commercial and wild bumblebees in Maine blueberry production, please see Maine Cooperative Extension Fact Sheets no. 302 and 630.

URGENT: Spotted Wing Drosophila Update

Monday, August 13th, 2012
By Frank Drummond
The state of Maine has secured a Section 18 “Crisis Exemption” registration for a higher rate of Malathion 8Fl that is more effective for the SWD than the lower rate on the existing label. This higher rate is in EFFECT on August 13 and only lasts for 15 days (August 13-28). If you decide to use this material at the higher rate very strict reporting is required by the US EPA. The forms for reporting can be acquired from the Maine Board of Pesticide Control.
Last week (Aug 10) spotted wing drosophila (SWD) showed up in a few more blueberry fields. We have found adult male flies in traps in TWO fields in Franklin (Hancock Co.), one field in Surrey, two fields in Ellsworth, one field in Harrington, and one field in Jonesboro. I (Frank Drummond) have also confirmed trapping of adult flies from several fields in Deblois (Washington Co.). Thirty wild blueberry fields are being monitored by the Maine Dept. of Agriculture and the University of Maine and many additional fields are being monitored by growers and so far the picture is that SWD appears very spotty across our blueberry growing areas. But, please be vigilant and continue to trap for SWD in fields that you have not harvested yet.
What to do if you do find flies? Well, there are several approaches, NONE of which are based upon experimental evidence from wild blueberry research in Maine. 
Conservative and most safe approach: as soon as 1 fly is trapped and confirmed apply a suitable insecticide at an interval that reflects the average persistance of kill (residual in table) of the material (see list of insecticides below).
Liberal approach: Coninue to trap after you catch your first fly and when fly numbers START to increase from 1 fly in a trap to 3, 5, 10, etc., then consider applying an insecticide.
Whatever strategy you pick, consider the following before applying an insecticide:
  1. If  you sell to a processor, check with them to see what material can be used.
  2. Make sure that the PHI for the material that you choose is in accordance with your harvest schedule.
  3. A PLANNED harvest 1-2 days after a confirmed trap capture may allow you to harvest the crop withpout making an application if you feel that you can get the berries out of the field immediately.

Currently Available Products for SWD Control

Spotted Wing Drosophila Alert

Tuesday, July 31st, 2012

Dear Blueberry Growers,

Many of you have started harvesting. The spotted wing drosophila has been found strawberry and raspberry fields in southern Maine so far, especially in the vicinity of Warren, where one trap in a strawberry field contained 98 SWD flies.

We are trapping 30 blueberry fields and found 1 SWD fly in a trap in a Franklin blueberry field, in the forest edge.

So, please be vigilant and keep trapping for this potentially devastating pest. I will provide an update when we trap more flies.

Frank Drummond