Hemipterans or sap-sucking insects excrete honeydew, a nicer term for poop. This order of insects, commonly called true bugs, comprises over 80,000 species, such as cicadas, whiteflies, mealybugs, coccids, psyllids, aphids, planthoppers, leafhoppers,
assassin bugs, bed bugs, and shield bugs. They range in size from 1 mm (0.04 in) to around 15 cm (6 in) and share a common arrangement of piercing-sucking mouthparts. Wikipedia
Hemipterans need to drink copious quantities of sap (phloem) in order to obtain the proteins and nutrients they need. As a result, they end up excreting a lot of unwanted sugar solution, making them quite popular among the other invertebrates. Honeydew is considered an essential carbohydrate source for pollinators, and it also supports the predators and parasitoids that keep pest insects in check. Honeydew isn’t as nutritious as pollen or nectar. However, it fills the bill as a special treat or when nectar is in short supply.
Aphids are generally considered not to have any good qualities, but honeydew is its saving grace. They have developed a mutually beneficial partnership with ants. The ants farm and protect the aphids, and in exchange, the ants get all the honeydew they want. This video captures the farmer ants hard at work: https://youtu.be/0TJT90MJmQg
As far as other creatures are concerned, honeydew is manna from heaven, but as usual, humans have a different opinion. Honeydew is a menace to some folks, particularly those living in urban areas. In some cities, such as Indianapolis, Indiana, it is a significant issue. Trees, specifically oak (Quercus spp.), seem to be the species most affected. Aphids and scale infect the trees and produce lots of honeydew. It drips on people, cars, sidewalks, outdoor furniture, and plants.
Jud Scott, a certified consulting arborist and owner of Vine and Branch Tree Care Company in Carmel, Indiana, says it falls like light rain, sticking to everything like glue, and then turns into a sooty mold.
Purdue University entomologist Cliff Sadof explains that the scale outbreak is brought on by stress, such as too much or not enough water, temperatures that are too hot or cold, wind, and root-zone soil disturbance from construction. Climate change also plays a role by making the trees leaf out before the beneficial insects can control the pests.
So, What Is the Knee-jerk Reaction By Humans?
Scott and Sadof recommend spraying the tree with systemic insecticides in early spring before the scale nymphs become adults. The nymphs eat the poisoned sap and die before they can become a problem.
Problem solved, right?
Actually, no. That solution creates an even worse problem. Do you recall the bumble bee massacre that occurred in Wilsonville, Oregon, in April 2013? Blossoming linden trees in a shopping center parking lot were sprayed with a systemic neonicotinoid insecticide early in the morning. A few hours later, foraging bees fell to the ground, motionless. An estimated 46,000 to 107,000 bees died from exposure to the toxic chemicals. The pesticide had been sprayed on the trees to keep shoppers’ cars from getting sticky with honeydew produced by aphids in the trees above.
The incident in Wilsonville is not a one-time thing. It has been repeated over and over again across the country. In the U.S., systemic insecticides are widely used to manage insect pests. However, they impact non-target beneficial insects as well, either directly through contact or indirectly through the food chain. Hemipterans that survive the treatment can excrete contaminated honeydew that is toxic to beneficial insects that feed on it. It’s a losing game for insects, no matter how you look at it.
So, What Is a More Straightforward Non-poisonous Solution?
There’s no need to drench the landscape with pesticides. Mother Nature provides a pest control service that works much better and keeps the natural balance in check. Parasitic wasps, lacewings, ladybugs, and other predators can keep pests under control. Whether you live in the city or country, they can be your best line of defense. Parasitic wasps will lay eggs in an unwanted insect, and the victim will become lunch for the larvae. Ladybugs have a voracious appetite and will consume hundreds of scale insects, aphids, and other pests.
All the beneficial insects ask for in return are some native plants, shrubs, and trees to provide shelter and food. Oh yeah, and a little honeydew on the side for a treat.