|An adult sunflower receptacle maggot fly, Strauzia |
longipennis. The larvae feed on the white cork-like
material within the head (or receptacle) of the sunflower.
|An adult black blister beetle, Epicauta pensylvanica. |
They pollinate flowers, consume grasshopper eggs as
larvae, can cause blisters if you touch them, and defoliate
alfalfa. So, are they beneficial or pests?
|A lacewing egg. Lacewings (Chrysopidae), are a |
natural predator of soft-bodied insects. They are
natural enemies of a number of soft-bodied insects
and mites. Sunflowers can make a good substrate
for egg laying.
I've been thinking a lot about sunflower as of late. Maybe because I recently harvested about an acre of the stuff. I decided to try my hand at a large sunflower insect control trial this summer. Now I'm in the midst of counting seeds for insect damage, taking hundredweights, and measuring yield. Next, we'll be splitting stalks and searching for injury from stalk-boring insects. All of this will be compiled into a year-end report that I will make publicly available either at the end of the year or very early next year.
I have similar kinds of efforts with other crops (for example, I'm sure I have more acres devoted to sugarbeet research). However, Helianthus annuus is a bit different in that the abundance of insect life that you can find on (or within) just a single plant is pretty impressive.
This abundance of insect life also places some particular challenges on their management. There are seed-boring and feeding weevils and caterpillars; flies and weevils that just feed on the head (just the bit that holds the seeds, also called the receptacle); caterpillars and leaf beetles that feed on the leaves; weevils and long-horned beetles that feed within the stalk; and scarab and click beetle larvae that feed on the roots. Ok, but these are just the insects that essentially "parasitize" the plant. Sunflowers have large flowers that attract many, many pollinating insects; from honey bees and bumble bees to beeflies and blister beetles and butterflies. In addition to flowers (usually a single, large flower per plant in cultivated sunflower), they also have extrafloral nectaries, particularly around the bud bracts, that provide a meal for beneficial insects such as adult parasitoids and ants.
It is all of this shared habitat between beneficial insects and pests that make sunflowers (and some other crops as well) so difficult to manage by some conventional methods. Certainly, host plant resistance against the insects that we do not want could be one useful route to go. However, because of the tricky nature of the Helianthus genome, this might take a while. My colleague and friend, Jarrad Prasifka, was recently hired up in Fargo, ND at the Sunflower Research Unit. Perhaps he will come up with a creative solution in the near future. Until then, I'm working on trying to use chemical applications through an IPM program but using products that might allow application before the buds break open and before chemical applications might negatively impact good insects, such as pollinators. I guess we'll see if I'm successful. In the mean time, I've go a lot of sunflower seeds to count and weigh...