natural enemies

Biological pest control: parasitoids

Maryland Grows3 Comments

¿Hablas español? Aquí esta una traducción: Control biológico de plagas: los parasitoides

Parasitoids are natural enemies of pests that, like predators (ladybugs and flower flies) can help us keep pest populations at bay or eliminate them from our gardens.

Parasitoid or parasite? Let’s learn the difference between these terms

Before saying more about this group of natural enemies, let me tell you that it is very common to confuse the term “parasitoid” with the term “parasite.” Parasites and parasitoids have in common the need for a host for their development. The difference between the two types of organisms is that parasitoids kill their host to complete their life cycle. That is, the parasite can live at the expense of the host without having to kill it, while the parasitoid ends up killing its host upon completion of its life cycle. Parasites are generally known to be annoying and even transmit diseases to animals, plants, and humans, while parasitoids are beneficial insects, as they help us control pests.

What is a parasitoid?

Parasitoids are insects that insert their eggs into the body or egg of another insect (host) in order to complete their life cycle. Parasitoids go through complete metamorphosis, four different stages of development: egg, larva, pupa, and adult. To finish their development, the parasitoids must feed on their host, and the females first deposit their eggs in their host. As soon as the parasitoid egg hatches, the larvae begin to devour the tissues of their host. Once the larvae reach a certain size, they become pupae, after which the adult emerges, killing the host.

Parasitoids can be classified according to their oviposition (egg-laying) behavior. Endoparasitoids are the parasitoids that lay their eggs inside the body or egg of their host. In contrast, ectoparasitoids oviposit on top of the body of their host, that is, on the surface of their body. To see these fascinating creatures in action you can, watch a video of endoparasitoids and one of ectoparasitoid activity.

Life cycle of an ectoparasitoid (adapted from Presa-Barra et al 2020)

life cycle steps of an ectoparasitoid

Life cycle of an endoparasitoid (adapted from Presa-Barra et al 2020)

life cycle steps of an endoparasitoid
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Hidden Garden Party: Who’s Eating Whom?

Maryland Grows2 Comments

aphids on cantelope leaf
Heavy aphid infestation on the underside of a cantaloupe leaf. Photo: Ashley Bodkins

Who loves a party? I know I do, especially a summer BBQ with all the family favorites! Insects are no exception and really know how to have some fun. Pictured above is a party of aphids, which are tiny little suckers — literally. They are soft bodied insects that suck plant sap with their piercing, sucking mouthparts.

aphid damage leaf curling
Twisted, deformed leaves are a symptom of aphid feeding damage. Photo: Ashley Bodkins

Aphids can come in many colors ranging from shades of green to black. They suck juice right from plant tissues, resulting in bent and twisted leaves as seen in the picture above. Aphids are generally only found on the underside of leaves and can be in very large numbers. Once a colony is established females can even reproduce without a male.

They secrete a sweet, sugary waste liquid that is called “honeydew”. Sometimes a fungus grows on the
honeydew, which is called sooty mold and looks like someone smeared coal soot on the plant.

Seeing ants on your plants can be your first sign that there is an aphid infestation. Ants love honeydew and often “farm” aphid colonies to reap the benefits.

ladybird beetle
The ladybird beetle is a natural enemy of aphids. Photo: Ashley Bodkins

Aphids can transmit plant virus diseases, but generally they aren’t found in large enough numbers to warrant a chemical control. Mother Nature actually Ahas some really interesting predators for aphids. In fact, the beautiful red with black spotted ladybird beetle (ladybug) is an avid aphid hunter and can eat more than 5,000 aphids throughout its four-part life cycle.

lady beetle larva eating an aphid
Ladybird beetle larva eating an aphid. Photo: Lenny Wells, University of Georgia, Bugwood.org

Other natural predators include lacewings, flower fly larvae, and parasitic wasps. Evidence of natural predators include “aphid mummies” which are light brown, hollow aphid bodies that were once inhabited by parasitic wasp larvae.

aphid mummies
Mummies of oleander aphids parasitized by Aphidius sp. wasp. Note the hole in the aphid at the top right of the photo indicating a wasp has emerged. Photo: David Cappaert, Bugwood.org

syrphid larva
Flower fly larva feeding on an oleander aphid. Photo: David Cappaert, Bugwood.org

Physical control of aphids can be accomplished by spraying the pests with a strong stream of water. This causes them to fall off the plant and hopefully disrupt their feeding. As a last resort, use chemical
controls such as insecticidal soap or Pyrethrum products.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland, edited by Christa Carignan, Coordinator, Home & Garden Information Center, University of Maryland Extension. See more posts by Ashley and Christa.