Last week, Kristie wrote a post on solifuges, some of the coolest arachnids around! This week, I'll introduce you to the awesome insect that I studied for my Masters research – the blackmargined aphid.
But what is an aphid? Aphids are very small insects, and they have rounded, soft bodies. They live on plant stems and undersides of leaves, and have a long mouthpart called a proboscis that acts like a needle to jam into the plant tissues to suck out the juices. Another totally cool feature of aphids is a pair of cornicles on their abdomen. They remind me of little biological exhaust pipes – but they secrete a kind of wax that coats the bodies of the aphids to keep them from drying out.
There is an easy way to distinguish blackmargined aphids from other species. The outer margins of their wings are lined with black (hence their name)!
One of the coolest things about aphids is their watery waste. It’s called honeydew. It’s mostly made up of sugars from the plant that the aphid didn’t process. And for blackmargined aphid, their honeydew is about 95% sugar. Part of my research dealt with quantifying how much honeydew blackmargined aphids produced, and figuring out how much energy was being removed from pecan trees.
So honeydew is both good and bad. It’s bad because if there is a lot of honeydew produced by a heavy infestation of aphids, it coats the pecan leaves. Because of the high sugar content, it’s the perfect place for sooty mold to grow. Growth of sooty mold means not enough sunlight gets to the leaves and photosynthesis is reduced. But it can be a good thing (in moderation!), too. The honeydew attracts lots of beneficial insects to the trees. These “natural enemies” feed on pest species – including blackmargined aphids – that have the potential to harm the tree.
Blackmargined aphids only feed on pecan trees. Both species are native to North America, and have co-evolved for thousands of years! Today, pecan is being cultivated in other parts of the world as well, and the blackmargined aphid has moved along with it.
- Most of the year, blackmargined aphid females reproduce by parthenogenesis, or cloning. But once the weather starts to get cold, male aphids develop and mate with females. Eggs are laid, and overwinter to hatch the following spring.
- Each adult blackmargined aphid can produced up to 32 generations of offspring.
- Despite the high sugar content, honeydew doesn’t actually taste sweet.
- Blackmargined aphids hold their wings flat against their backs, while other yellow pecan aphids hold their wings pitched over their bodies.
When I first started my research, I didn't really know much about aphids. But once I started studying them and learning more about their behavior and biology, the more fascinating they became. Now, they're one of my favorite insects!
If you have pecans around where you live, check some of the leaves around May - June to see if you can find blackmargined aphids. You can also see if you have other species on different plants. Just look for the squishy bodies and cornicles!