Phoresy

Phoresy describes the relationship between two organisms in which one is a hitchhiker, but not a parasite.

The fleas that catch a ride on your dog or cat are parasites. They catch rides and then drink the blood of our beloved pets. This is not phoresy. Now, picture a person riding a horse. Person plus horse equals phoresy. The person is being transported by the horse, but is not a parasite.

In many cases, electron microscopy is needed to actually see phoresy in action. And many phoretic insects lose the ability to catch a ride once they have reached a destination. Like many other insects, those that use phoresy may go through several very different life stages, such as phoretic, parasitic, and reproductive stages.

​In nature, phoresy can bring both pests and beneficials to your garden. Here are just a few of the situations in which phoresy occurs.

Pseudoscorpion on the leg of a Crane fly (Vincenzo Turi) CC BY-SA 3.0

Hummingbirds

We may love to see hummingbirds flitting through the garden, but you should be aware that hummingbirds may carry flower mites. Flower mites are tiny, nectar stealing pests that run up a hummingbird’s beak as it feeds. Grabbing ahold of the hummingbird’s nostrils, flower mites then go for a wild ride in hopes of reaching a new food source. When the hummingbird stops to feed at a different flower, the mite runs down the hummingbird’s beak to gorge on as much nectar as it can before hopping another ride to yet another flower.

Honey bees

Moving in the opposite direction, it has recently been discovered that varroa mites, the bane of honey bees, are phoretic. These devastating parasites of the honey industry lie in wait for unsuspecting honey bees to visit a flower. As the bee collects nectar and pollen, varroa mites catch a ride that ultimately takes them to the hive. These parasites suck the life fluids from developing and adult bees. These pests also carry viruses that infect honey bees. Varroa mite infestations can kill an entire hive, if left untreated. Varroa mites are just one aspect of the global problem of colony collapse disorder.

Ground bees

Male ground bees are seduced by blister beetle larvae into carrying them to female ground beetles, phoresy style. Blister beetle larvae emit a pheromone that is similar to the perfume used by female blister beetles to attract males. When male ground bees approach, the blister beetle larvae attach themselves to the male bees. After recovering from their disappointment, the male bees continue their search for a female. When she is found, the male bee blindly does his business as the blister beetle larva moves to the female bee. When she returns to her nesting area, the larva jumps off and begins feeding on everything it can - nest, provisions, and eggs.

Pseudoscorpion holding onto adult fly’s femur using pincers (Sarefo) CC BY-SA 4.0

Pseudoscorpions

Pseudoscorpions are tiny beneficial insects that feed on ants, thrips, small flies, springtails, carpet beetles, clothes moth larvae, booklice, and spider mites. They also get around using phoresy by catching rides on many different flying and crawling insects. In some cases, they even provide a service to the carrier insect by eating its parasites along the way!

Parasitic Wasps

One phoretic wasp, Trichogramma, catches rides on mated female imported cabbage moths to reach areas where eggs have been laid. These beneficial wasps then parasitize the eggs, making our jobs as gardeners so much easier. Research on this behavior is new, but very exciting!

Greenhouse pests

Greenhouses provide the warmth, sunlight, and moisture that plants need to thrive. The same is true for thrips, whiteflies, leafhoppers, and fungus gnats, just to name a few. While reputable greenhouse growers do their best to eliminate pest phoresy on the plants they sell, it still happens. Many imported pests and diseases are brought into new areas through phoresy. When you bring plants home, you also risk bringing phoretic pests and diseases. This is why it is so important to create a quarantine area. Forty days and nights goes a long way toward sorting out and preventing more serious problems.

So, quit "phoresing" around! Go take a closer look at your plants and the insects that call them home. You may be surprised to see what’s out there!