Archive for the ‘Insect Updates’ Category

Spotted Wing Drosophila (SWD) July 8, 2013

Monday, July 8th, 2013

It is no wonder with this HOT weather over the 4th and following weekend a few more SWD captures have surfaced since my update on July 2nd.  However, last week’s capture of a male SWD in Cherryfield was a misdiagnosis. When we looked at it, two spots were found on each wing and so we have NOT had a recent SWD capture Downeast yet. But, in the south…male SWD were captured in Dresden and Whitefield on July 3rd in the southern coastal blueberry-growing region. On Saturday, July 6th, I found a male SWD in a Winterport blueberry field. I have deployed 20 traps in this field and only ONE trap had an SWD. I also have 25 traps deployed in a Stockton Springs field, but as of yet no male SWD have been identified and I have not had a chance to go through all the traps for microscopic detection of females yet.  I am guessing that from the low number of captures that SWD has not completed its first generation, producing new adults.

An important and timely question…What shall I do if I detect male SWD in traps in my field at this time of year (early July)?  I think the thing to first state is that if you have only a slight proportion of ripe (blue) berries (< 0.5 % or so) then don’t panic. At this point I believe ONLY the overwintererd SWD are in our fields as of yet and SWD needs RIPE fruit to lay eggs in. However, they will attack these fruit and start to build in numbers over the next several weeks. So, there is a trade-off between: 1) starting to protect your crop too early with insecticides and having to spray many times prior to harvest and 2) incurring damage and fruit loss. Each grower has to strategize to solve this dilemma of whether to take action or not.

ONE WAY of finding a solution to this problem is to determine at what percent of ripe fruit in your field is the trigger for action.  As an example…If you typically get 2,500 lbs / acre on a given field and guessing on past prices you can estimate what you will get for your crop…then you can calculate how much loss in revenue you will incur if SWD takes 1, 2, 5, 7%, etc., of your crop and you can determine what the economic threshold would be…or in other words the cost of crop loss that will equal the cost of controlling SWD (application + insecticide cost). So, in our example if you normally get $0.75 / lb, then 1, 2, 5, and 7% infestation EARLY in the season will cost you…25, 50, 125, or 175 lbs / acre or in dollars…$18.75, $37.50, $93.75, or $131.25…in this case if it costs you $100/acre to treat the crop then somewhere between 5 – 6% crop loss would be your decision making trigger to treat, meaning 5 – 6% of your crop being ripe.

The calculation above is ONLY a guide. Growers are different in their aversion to risk and price that they receive and so it is not possible to give a simple one answer that fits all.  BUT, this being said another thing you might want to consider prior to an insecticide application is to take a known sample of ripe fruit from your field (small collections from several locations throughout field). Place a quart of your fruit in a gallon zip-lock baggie and mix a salt solution of 1/4 cup salt to 4 cups water.  Lightly crush the berries in a bag and add the salt solution.  Allow the fruit to sink to the bottom of the bag and wait approximately 10-15 min.  Several baggies can be easily set up if you want to sample more than 1 quart of fruit. If the fruit is infested, the larvae should float in the solution for you to visually inspect (See my SWD factsheet showing what larvae look like).  NOW you have a better idea of crop loss that exists at the time of sampling.

The last aspect of EARLY SWD management that I want to bring to your attention comes from my inspection of blueberry fruit fly traps this past Sunday in the field. I was at a field in Stockton Springs and the threshold (10 cumulative flies / trap) was already surpassed at 13 flies / trap. So, if this grower is thinking about a perimeter spray (a location where we also tend to capture lots of SWD)…then an insecticide that is ALSO effective against SWD would be a logical choice. An insecticide that would NOT a choice is imidacloprid (ADMIRETM, PROVADOTM, MONTANATM, PREYTM, etc.) since efficacy against SWD is low. Reduction of SWD adult numbers as a result of a perimeter blueberry fruit fly application might buy you some more time before you need to manage for SWD or maybe even allow you to harvest early making an insecticide treatment specifically for SWD not necessary. However, at this point we do not know how this might play out and so it is no guarantee that spraying for blueberry fruit fly will have any effect on SWD.

*A NOTE…for organic growers the above points are also relevant. Insecticide options are EntrustTM or PyganicTM. The capture of SWD may also be a trigger for deploying exclusion netting over your crop or for deploying a grid of bait cups (every 25 ft) throughout exceptionally high yield areas of your field as a trapping out tactic.      

NOTE: SWD updates will only be made when we have trap captures.

Spotted Wing Drosophila Update for July 3, 2013

Wednesday, July 3rd, 2013

Dave Yarborough and Frank Drummond will be sending out SWD updates 1-2 times a week over the growing season. Frank and Judy Collins will be monitoring 18 field sites from Stockton Springs up to Jonesboro. Dr. Jim Dill and Dr. Dave Handley (UMaine Cooperative Extension) are monitoring traps in mid-coast to southern Maine in strawberry, highbush blueberry, and raspberry fields. In addition, we will be in contact with several growers from the coastal region. Therefore, we should have a good monitoring network this year!

July 2 update: Many growers have traps out now. I have not verified ANY SWD captures at this point. Very early in the season (May) an individual SWD was captured Downeast, but this was part of the overwintered population still in hibernation. I have verified at “look-alikes” to the SWD in southern, coastal, and Downeast Maine, but again as I stated NO CONFIRMED SWD HAS BEEN CAPTURED IN MAINE AS OF TODAY. This morning I received an email from a grower in Cherryfield that stated they caught a male SWD in their strawberry field. I will be checking this out to verify the capture shortly and let you know next week. 

In the meantime, don’t forget about the blueberry larvae (BFF) threat. Get your traps out for them also. BFF was trapped last in Waldoboro, Maine last week. No need to panic as they have just started emerging in the coastal area AND adult females need 7-10 days of warm weather before they are capable of laying eggs in to RIPE fruit (which is only starting to appear in noticeable proportions in the coastal region.  

NOTE: SWD updates will only be made when we have trap captures.

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. 

DISEASE IN MAINE BUMBLEBEES AND THE USE OF COMMERCIAL BUMBLEBEES (Part One)
 
(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. 
___________________________

DISEASE IN MAINE BUMBLEBEES AND THE USE OF COMMERCIAL BUMBLEBEES (Part Two)

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