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| Honey bees and native pollinators active in early summer blooms. Raleigh, NC. Photo: HJB |
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| Carpenter bee foraging on salvia. Photo: HJB |
Sunday, May 27, 2012
Upcoming pollinator presentation at NC State
Wednesday, May 23, 2012
Do it yourself: An update on distinguishing SWD larvae from other insects in strawberries
Early this spring, I wrote a post discussing how to distinguish spotted wing drosophila (SWD) larvae from other internally feed insects. That post was focused primarily on blueberries. This spring and early summer, however, I received several calls about SWD in strawberries, and they appeared in our research plots for the first time.
Fortunately, the majority of grower calls I received about larvae in strawberries ended up being sap beetle larvae rather than SWD larvae. Sap beetles or picnic beetles are actually a complex of beetle pests which include at least three species in North Carolina (Carpophilus lugubris, Stelidota geminata, Glischrochilus quadrisignatus, and others) and are attracted to rotting, not sound fruit. If rotting fruit are present near sound fruit, as can commonly happen when you-pickers aren't thorough or rain prevents picking, sap beetle adults and larvae can also attack sound, otherwise marketable fruit.
While sap beetle larvae are also not desirable in strawberries, they are more easily controlled than SWD. Good sanitation, meaning removal of overripe or rotting fruit, is usually enough to keep sap beetle populations in check.
How, then, can you distinguish between sap beetle larvae and SWD?
Host fruit
Sap beetles will first attack overripe, rotting, or otherwise damaged fruit. SWD will be found in fruit that appears otherwise marketable until cut open. As SWD grow older, fruit condition may deteriorate, but fly larvae found in sound fruit are more likely to be SWD than those found in rotting fruit.
Size
Young sap beetle larvae may be similar in size to large SWD larvae, but in general they will be larger than SWD larvae. Size on its own is not a good determinant, but it can be a good initial indicator.
Appearance
SWD larvae lack legs, have no distinct head, lack hairs or bristles, and are tapered on both ends (see here for more images). Sap beetle larvae have distinctive head capsules, three pairs of legs, and bristles along their bodies. Adult sap beetles may also be present along with larvae.
What other insects might be present inside strawberries?
Corn earworm (Helicoverpa zea) are occasional pests of strawberries, and the larvae can tunnel into berries. Corn earworms are caterpillars, which means they have a distinctive head capsule and three pairs of front legs like sap beetle larvae, but they also have short, grippy prolegs along their abdomen and have a pattern of stripes along their body (although their appearance can be highly variable as larvae age).
Fortunately, the majority of grower calls I received about larvae in strawberries ended up being sap beetle larvae rather than SWD larvae. Sap beetles or picnic beetles are actually a complex of beetle pests which include at least three species in North Carolina (Carpophilus lugubris, Stelidota geminata, Glischrochilus quadrisignatus, and others) and are attracted to rotting, not sound fruit. If rotting fruit are present near sound fruit, as can commonly happen when you-pickers aren't thorough or rain prevents picking, sap beetle adults and larvae can also attack sound, otherwise marketable fruit.
While sap beetle larvae are also not desirable in strawberries, they are more easily controlled than SWD. Good sanitation, meaning removal of overripe or rotting fruit, is usually enough to keep sap beetle populations in check.
How, then, can you distinguish between sap beetle larvae and SWD?
Host fruit
Sap beetles will first attack overripe, rotting, or otherwise damaged fruit. SWD will be found in fruit that appears otherwise marketable until cut open. As SWD grow older, fruit condition may deteriorate, but fly larvae found in sound fruit are more likely to be SWD than those found in rotting fruit.
Size
Young sap beetle larvae may be similar in size to large SWD larvae, but in general they will be larger than SWD larvae. Size on its own is not a good determinant, but it can be a good initial indicator.
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| Sap beetle larva on knife blade. Photo from a commerical strawberry farm in eastern NC, 2012. |
SWD larvae lack legs, have no distinct head, lack hairs or bristles, and are tapered on both ends (see here for more images). Sap beetle larvae have distinctive head capsules, three pairs of legs, and bristles along their bodies. Adult sap beetles may also be present along with larvae.
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| Sap beetle larva. Note the three pairs of legs, the distinctive brown to black head capsule and the bristles along the body. Sap beetle larvae will be mostly white or cream colored and lack patterns on their body. Photo from a commerical strawberry farm in eastern NC, 2012. |
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| Two spotted wing drosophils larvae (center) inside a day neutral strawberry, Upper Mountain Research Station, October 2011. Photo: HJB |
Corn earworm (Helicoverpa zea) are occasional pests of strawberries, and the larvae can tunnel into berries. Corn earworms are caterpillars, which means they have a distinctive head capsule and three pairs of front legs like sap beetle larvae, but they also have short, grippy prolegs along their abdomen and have a pattern of stripes along their body (although their appearance can be highly variable as larvae age).
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| Corn earworm larvae feeding on strawberries. Photo via UC IPM. |
Friday, May 4, 2012
What should growers and homeowners who find SWD do?
I am getting reports of spotted wing drosophila SWD larval activity in some southeastern locations over the past two weeks, and we have observed SWD infestation in some of our research station plots in North Carolina. Infestations in my plots are a good thing, because it allows us to study SWD here and provide you with up to date information, but infestations in grower fields are another matter. We have been catching adult SWD since January in North Carolina, but these are the earliest larval infestations we have recorded in the state. This early activity has prompted several questions about what growers or homeowners should do if they find SWD infested fruit. Here's a quick summary of the four key steps you should take in the event of SWD infestation:
1. Remove all ripe and ripening fruit and destroy it (by freezing, "baking" in the sun inside a clear plastic bag for a few days, or removing from the site). Eggs or larvae may be present in otherwise sound appearing fruit. Leaving this fruit means that potentially infested fruit is present and could be harvested.
2. Begin an aggressive (once per week if it does not rain, reapplication in the event of rain) spray program. Rotating between at least two modes of action will reduce the likelihood of resistance development. See here for information about the probably efficacy of registered insecticides in southeastern small fruit crops. Because these efficacy ratings are based on work done largely in the western US, where environmental conditions differ, they are not set in stone. We are running several efficacy trials as I type and hope to have NC specific data by mid summer.
3. Practice excellent sanitation. Remove all ripe fruit and sell or destroy it. Do not discard culls in the field, and clean up after rain and u-pickers. Unpicked fruit is a reservoir for SWD larvae.
4. Sample fruit regularly and consider trapping flies. Traps tell you SWD presence or absence and are not perfect, but they are helpful. Place traps in strawberry rows, near fruit for the best chance of catching flies. Sample fruit each harvest by either cutting them open and looking for larvae, crushing them in salt water (1/4 cup salt per gallon), or freezing them. Salt water and freezing will cause larvae to exit fruit. Sample at least 30 berries per field. See here and here for trapping information and here for larval sampling information.
All growers are strongly encouraged to monitor for SWD adults before larvae are found. If adults are present and fruit are ripe, pesticide treatments are recommended through the end of harvest. We hope that this strategy will prevent larvae from showing in fruit and triggering the actions listed here.
Update, June 22, 2012
I am aware that homeowners may be not be able or may prefer not to use insecticides on fruit in the gardens are yard. Unfortunately, sanitation alone will not eliminate and SWD population. However, if you can pick your fruit a bit earlier or a bit less ripe, it will be exposed to SWD for less time and will perhaps be at a lower risk of infestation. It's also important to note that while SWD larvae cause fruit to decay quicker and are unpalatable if present in fruit, they are not poisonous or parasitic. If you have inadvertently consumed fruit from your home garden that SWD larvae have been present in, they do not pose a heath risk.
Update, August 7, 2012
I have been reading LOTS of scientific papers about SWD in the last week. A couple of Japanese references suggest that mesh cages or bags (specifically 0.98mm mesh) prevented SWD infestation in blueberries without impacting plant growth. We use mesh bags a lot to either keep insects we are studying in or to keep insects we don't want out.
This strategy is worth a shot for homeowners who can tolerate the sight of bags on their plants. In order to exclude SWD, cages should be placed before fruit begins to change color and tightly sealed at the bottom. We'll often place a piece of quilting foam between the cage and the stem of the plant to allow us to tightly tie the cage shut (with a zip tie or twine) but protect the stem from damage. Cages should stay in place until you harvest your fruit. We use organdy mesh from fabric store and sew our cages to size, but paint strainers also work in a pinch. I plan to try this method with my backyard blueberries, blackberries, and figs next year and will be interested to hear if others also give it a shot.
1. Remove all ripe and ripening fruit and destroy it (by freezing, "baking" in the sun inside a clear plastic bag for a few days, or removing from the site). Eggs or larvae may be present in otherwise sound appearing fruit. Leaving this fruit means that potentially infested fruit is present and could be harvested.
2. Begin an aggressive (once per week if it does not rain, reapplication in the event of rain) spray program. Rotating between at least two modes of action will reduce the likelihood of resistance development. See here for information about the probably efficacy of registered insecticides in southeastern small fruit crops. Because these efficacy ratings are based on work done largely in the western US, where environmental conditions differ, they are not set in stone. We are running several efficacy trials as I type and hope to have NC specific data by mid summer.
3. Practice excellent sanitation. Remove all ripe fruit and sell or destroy it. Do not discard culls in the field, and clean up after rain and u-pickers. Unpicked fruit is a reservoir for SWD larvae.
4. Sample fruit regularly and consider trapping flies. Traps tell you SWD presence or absence and are not perfect, but they are helpful. Place traps in strawberry rows, near fruit for the best chance of catching flies. Sample fruit each harvest by either cutting them open and looking for larvae, crushing them in salt water (1/4 cup salt per gallon), or freezing them. Salt water and freezing will cause larvae to exit fruit. Sample at least 30 berries per field. See here and here for trapping information and here for larval sampling information.
All growers are strongly encouraged to monitor for SWD adults before larvae are found. If adults are present and fruit are ripe, pesticide treatments are recommended through the end of harvest. We hope that this strategy will prevent larvae from showing in fruit and triggering the actions listed here.
Update, June 22, 2012
I am aware that homeowners may be not be able or may prefer not to use insecticides on fruit in the gardens are yard. Unfortunately, sanitation alone will not eliminate and SWD population. However, if you can pick your fruit a bit earlier or a bit less ripe, it will be exposed to SWD for less time and will perhaps be at a lower risk of infestation. It's also important to note that while SWD larvae cause fruit to decay quicker and are unpalatable if present in fruit, they are not poisonous or parasitic. If you have inadvertently consumed fruit from your home garden that SWD larvae have been present in, they do not pose a heath risk.
Update, August 7, 2012
I have been reading LOTS of scientific papers about SWD in the last week. A couple of Japanese references suggest that mesh cages or bags (specifically 0.98mm mesh) prevented SWD infestation in blueberries without impacting plant growth. We use mesh bags a lot to either keep insects we are studying in or to keep insects we don't want out.
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| We have used mesh bags in blackberries to exclude thrips from developing fruit in order to determine if they impact fruit development. They don't appear to. |
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