Eupeodes americanus is a hoverfly species with a range from Alaska to Mexico – and maybe beyond and even in Europe. Hoverflies are often mistook for bees – or so I hear. They do have yellow/black or white/black markings, but unlike wasps or bees, they have short antenna, enormous fly-eyes, and only one pair of wings. Plus they hover, are usually smaller than a typical well-known wasp or bee and they do not sting.
Hoverflies are also known as flower flies, and syrphid flies. Many are aphidophagus or polyphagous (meaning they eat aphids or many prey). However, only their larva eat other insects. In all cases, the adults simply eat pollen and nectar and are therefore important pollinators.
Imagine! An insect that is both an effective pollinator and a predator of aphids and other soft-bodies pests? How wonderful.
The truth is, most things fliying around your yard contribute to pollination. Despite the resent cries to save the bees (which in most cases is referring to honeybees, which are an introduced species), little attention is placed on the other pollinators – the native ones. Sure, the number of flowers a native bumblebee visits and the enormous amount of pollen it can transport makes it impressive, but the immeasurable number of flies, midges, and even mosquitoes, make them similarly important as they all contribute heavily to pollination. – I know, I too want to think mosquitos are useless and should probably be wiped-off the planet, but they do play an important role.
Back to hoverflies – a study by the University of Exeter in the UK found that 4 billion hoverflies migrate to the UK every year from other parts of Europe and Africa. They eat, and mate and more than 4 billion leave Great Britain in the fall. They, therefore, are carrying billions more particles of pollen and nutrients and are therefore a significant part of pollination, biodiversity and biomass.https://www.mpg.de/13730049/hoverflies-migration see for more.
While little is known about most hoverfly species, it is suggested that Eupeodes americanus also migrates, since its North/South range is so extensive. From studies in California and observations through the temperate latitudes it is believed that E.americanus is a shoulder-season insect, preferring the cooler autumn and spring months. But again, if the migration theory is correct, then it may just be these shoulder months when the hoverflies are passing through.
So, other than pollination, what do these hoverflies do as they pass through? Some hoverflies are known to lay up to 400 eggs in their short 3-4 week lifespan. E. americanus eggs last two days, and for the next 7 days, they are aphid-eating machines! At the third instar stage (last 1/3 of their larva stage) each larva can consume up to 70 aphids – that’s likely around 35/day. Better yet, unlike ladybugs, which cause defensive actions in aphids, hoverfly larva seem to illicit no defence response so the aphids are less likely to drop or spread or repel the predation. The ladybugs in that trial could only eat 1/3 as many aphids as E. americanus. (E. Lucas, et al. University of Quebec at Montreal).
Hoverflies are strong fliers. Not only can they hover, but their flight speed is high and movements are direct. They hover to detect predators (ambush-spiders) on flowers, but also to find individual aphids. Because of a high cannibalization rate, hoverflies prefer to spread-out their eggs. As such, individual eggs are laid directly amongst aphid colonies. When the predator-in-waiting hatches and destroys the aphids, it then needs to pupate. E. Americanus will drop to the soil or dead leaf-debris to pupate, other species may pupate directly on the undersides of leaves….usually on older leaves where there are fewer predators. 5 to 7 days later, adults emerge, look for flowers and nectar, and 5 days after that, are ready to lay more eggs.
If you are gardening: Outdoors you can promote hoverflies by (first) spraying no chemicals. Second, plant high pollen/nectar producing plants, particularly ones flowering in the shoulder season: alyssum, sunflowers…etc. Ensure that these flowers are bedded in a mulch that will stay relatively cool. Also, don’t be in a hurry to rinse off early aphid colonies. If you’re really adventurous, provide plants that attract aphids, so they will attract hoverflies (and other predators) and reproduce right in your yard. Consider early season brassicas, midseason nasturtiums and soft, fresh growth in the fall when other plants are hardening-up. And, if you love these guys, or have important early crops that need pollution (like Apples), you may want to purchase some to release. We had a late winter here last year, and as a result many pears went unpollinated this year. Had E.americanus been released, some pollination may have taken place, and early season aphid control would have been in place as a result. You can buy E. Americanus through our distributors found at www.appliedbio-nomics.com
Greenhouses growers: If you are unscreened, you likely have these guys coming in from time to time. If you are screened, you should buy some. But, you must consider: You will receive hoverflies commercially as pupa or newly emerged adults. They need 5 or more days of feeding on pollen and nectar before laying eggs. If you have a non-flowering mono-culture, do not release E.americanus. If you have a crop with extra-floral nectaries, you may want to supplement with bee pollen. If you have pollen and no nectar, you can try to supplement with cotton pads soaked with 2:1 water to honey and hung amongst the plants. Or, as is best, grow some buckwheat or alyssum now, (a few plants on a weekly basis) and start putting them out amongst your crop. First, they’ll attract other predators, but when you release the hoverflies, they will feed at the alyssum and then look for your aphids.
Cannabis in a bunker: Good luck! You’re growing plants unnaturally, and therefore the predators will have a tough time. If it is medical grade you will not be able to supplement with either pollen or honey-water, nor can you bring any flowering plants in. Even if the female cannabis can be fed on by hoverflies for their nectar requirement the absence of pollen will prevent them from developing any eggs. However, it may be worth trying them (I have a few trials on the go right now) because they may be the only predators who fly strong enough to be affective in your high-windspeeds. So, consider this: Outside of the growth chamber get a cheep butterfly cage (through amazon) and grow some alyssum or buckwheat. When you buy your E.americanus adults, let them emerge within the cage with the flowers present and after 5-7 days release the adults into your growth chamber. (You should also reduce the windspeed at this time if you can). The females may immediately lay eggs near aphids. But, they will likely die without food within a day or two, so weekly purchases might be necessary. It’s worth a try if you aren’t willing to slow your fans, stop spraying for mildew, and use the most affective Aphidoletes aphidimyza or brown lacewing (Micromus variegatus)
Quick note: If you are going to provide supplemental flowers for the hoverfly (or any insect) DO NOT buy them from a store unless retailers can guarantee no pesticides, systemics or “natural” residues are on the plant for the entire life of the plant. Flies are particularly susceptible to chemicals. It is always best to grow your own plants from non-treated, organic seeds. (Even seeds can be treated with nionics.) Furthermore, supplementing with honey and pollen needs also the consideration of chemicals residues. Do not buy honey from Asia. And seeing as no honey or bee pollen can be “organic” because we don’t know whose plants they are visiting, it is best to carefully source out high quality honey and pollen.
This is an important insect to know. Chances are you’ve seen it and maybe you wondered what it was. If you ever saw one of its slug-like larva, it’s likely you did not connect it with its beautiful adult stage. I’m hoping that now you have enough information to recognize it, see if it is effective and are comfortable promoting it in your crop/landscape. Should you find it particularly useful, then please don’t hesitate to order some. I’m happy and proud to be the first in North America to commercialize this effective, native aphid predator, and to have done so partnering with Vineland Research in Ontario, and the University of Quebec at Montreal. And I’d love to hear how it has established wherever you are.
I want to give a special thanks to Dr. Dave Gillespie, for some of the beautiful photographs of our Hoverfly.