My Amaryllis bulbs are infected with syrphid flies. I have dug them but don’t know what to do with the bulbs. What can I do to save them?
Until receiving your question, I had always known of syrphid flies as beneficial insects in the garden, so I considered the possibility that the bulbs might be infested with bulb mites, or mealybugs, which are fairly common pests of Amaryllis. That being said, in my research to answer your question, I came across an article by Whatcom County Washington State University Extension agent Todd Murray which describes the Narcissus bulb fly, which is indeed a syrphid fly, and does sometimes infest Amaryllis bulbs. Excerpt:
Monitoring and Management: There are no pesticide recommendations available for these bulb flies. But that’s O.K.; we have many alternatives that we can use to avoid mushy bulbs. You should be thinking about trying these practices if you have a problem with bulb flies.
- In May, on sunny days look for large bumblebee-like flies hovering around your flowers. Bumblebees will have two pairs of wings while bulb flies will have one. Grab your handy insect net (you all have one, right???) and catch the critters before they can do too much egg laying. This sounds tedious, but is very effective for protecting small plantings of susceptible bulbs. Remember, each female fly can lay up to 100 eggs! Plus, if it is a nice sunny day, you should be outside admiring and tending your garden anyway.
- Adult flies use visual cues and smell to locate your delicious bulbs. After you have enjoyed your flowers, cover the bulb bed with a floating row cover, like Reemay*. Another recommendation given suggests that you mow down the vegetative portions of your plant and gently cover the tops with soil. Female flies will be unable to locate the bulb. Once no new foliage is sprouting, remove and store
the bulb through the off-season. If you do this, I do not know the impacts this will have on next year’s flower. That vegetation produces the bulb’s energy reserve that is needed for next year’s growth. Regardless, the earlier you can pull your bulbs out, the better chance that you will avoid bulb flies. - Bulb flies are less active in open, windy areas. Plant your beds in exposed windy places, if your landscape provides this type of climate.
- Avoid any damage to the bulbs when handling and planting. The lesser bulb fly prefers damaged goods to healthy bulbs. Establishment of maggots is much easier if there are already rot producing organisms in the bulb.
- Plant your bulbs deep, if they can tolerate it. Bulbs planted 25cm (or about 10″) deep in the soil will evade attack by adult flies. I am unaware if planting this deep is practical.
- When the time comes to pull up the bulbs, check the basal plate of each bulb. When you purchase new bulbs, check the plate for any signs of squishiness and rot. If you find some rot there, do not plant them and discard the rotten bulbs.
- Infested or suspicious bulbs can be cleaned of maggots by soaking bulbs in hot water (43-44 C) for at least 40 minutes. Care must be taken to not exceed this temperature, because you will damage the bulb. This is a great way to kill other pests of bulbs, too.
- Finally, if the problem persists, the sure-fire way to avoid bulb flies is to buy your flowers at the store like all the non-gardeners and black-thumbers out there. If you don’t plant it, they won’t come. This option is the one that I’m going to take now.
In the event that there are other pests present on your bulbs, this information from University of Florida Extension may be of interest. Excerpt:
“Spider mites are tiny animals (1/50 inch or 0.5 mm long) that cause injury similar to that of sucking insects as they feed on the leaves of amaryllis during warm, dry periods. Bulb mites attack rotting bulbs and tunnel into healthy bulbs, transmitting organisms that produce bulb rot.
Bulb mites are particularly damaging to bulbs of amaryllis.
Mealybugs are soft-bodied insects covered with a white, waxy material. When mature, they vary from 1/50 to 1/3 inch (0.5 to 8.5 mm) in length. They damage plant foliage by sucking plant fluids and may invade stored bulbs. Some control can be obtained by frequent syringing with a hose.”
In case you are curious, here is information on the beneficial properties of syrphid flies, from University of California, Davis Integrated Pest Management.