We are familiar with parasites like mosquitoes that suck blood essential for egg development. Females are parasitic and males are not. Males seek nectar and so do females for general energy requirements. The female needs blood proteins for egg development. After sucking blood, she takes a few days to digest blood protein that serves egg yolk development.
If a female survives the effort of sucking blood, she might lay 100 to 200 eggs on water surfaces after she has processed blood proteins to adequately nourished eggs. Only two of her eggs survive to reproduce if the mosquito population remains stable from one generation to the next. That is the norm. Some species lay eggs in unique ways to meet specialized nature niche adaptations. Population abundance has seasonal peaks.
Most mosquito parasitism occurs at dawn and dusk. We avoid harassment by selecting outdoor activity times and locations. Instead of using yard pesticides, we mechanically manage vegetation. Near the house we mow a 20-foot wide area that is avoided by most mosquitoes. Beyond the mowed area is a lush display of maiden pink and Cat’s-ear flowers (Fig 1) that please our eyes in June and house insect predators that help control parasites and parasitoids. Learning to live with nature has rewards. Sterilizing the yards diminishes the wonders of life that enrich our lives. It prevents bird habitation and beneficial insect predators important to landscape ecology.
Parasites do not normally kill their host. Mosquitoes carry parasites like the malaria amoeba that kills a half million people annually. There is a middle ground between the impacts of parasites and parasitoids. Most things exist on a gradation. To be most effective a parasite captures needed substances from a host without killing it.
Parasitoids kill their host. If parasitoids were completely effective, the host species would become extinct. Host species have structural and behavioral adaptations that help them complete their life cycle and reproduce. Parasitoids are more effective at controlling pests than predators and they are more susceptible to pesticides.
The adaptations of a parasitoid are for an adult to find a suitable host and lay eggs on or in the animal. Sphinx moths and large silk moths are sought by tiny specialized Braconid and Ichneumonid wasps. They sting the caterpillar to lay eggs. Tachinid flies lay eggs on the caterpillar. When hatched, larvae burrow in.
The host larva often jerks and waves its body to prevent parasitoid egg laying. Some caterpillars like the Federally Endangered Karner Blue Butterfly are ant tended. The butterfly secretes “honey dew”, a sugar solution, that ants eat. Ants protect the caterpillars from both parasites and parasitoids. Perhaps you have had ants jump off plants and bite you if you got too close to a caterpillar they protect. The Edwards Hairstreak butterflies are ant protected. Ants herd the caterpillars from oak leaves where they feed at night to the ground in the morning and back to leaves at dusk. Ant behavior, is similar to farmers herding cows to and from barns.
Once the parasitoid larvae of wasps or flies hatch from the egg, they feed on the least essential body tissues like caterpillar fat. The caterpillar goes about daily feeding to meet its energy needs for pupal development to transform to an adult. As it nears the pupal forming stage, it often has inadequate stored nutrition to complete pupal formation. Finally, vital organs are consumed by the parasitoid. Parasitoid and parasite activity exist in other organism groups. The few examples presented are simply representative to introduce their roles.
When you explore wild areas of your yard or neighborhood, you might find a shriveled desiccated caterpillar skin or one with obvious white pupae on the surface of a living individual. It is common for 100 or more parasitoids to emerge from the caterpillar’s body. If the parasitoid killed the caterpillar quickly, it would not survive to adulthood and its own species would parish.
Ask plant nurseries that sell native plant genotypes, buy cultivars minimally, and use minimal pesticides to enjoy life’s abundance. Such practices will maintain Earth’s biodiversity and enhance your life’s enjoyment.
Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at firstname.lastname@example.org – Ody Brook Nature Sanctuary, 13010 Northland Dr. Cedar Springs, MI 49319 or call 616-696-1753.