Insects that elude predators will elude pesticides, too

By Julie Banken
WSU Chelan/Douglas County Master Gardener

red crabapple on branch
A sting on a crabapple shows where a codling moth larva emerged after feeding on the fruit and its seeds. Living inside fruit is one way insect larvae protect themselves from predators. It happens to be a good way to avoid exposure to pesticides, too. – Provided photo/Julie Banken
Julie Banken
Julie Banken – WSU Master Gardener intern – Provided photo/WSU Master Gardeners

Compare a caterpillar to a butterfly or a maggot to a fly; newly hatched insect larvae don’t appear to be remotely related to the adults they will become. Not only do they look different, they have entirely different lifestyles than their adult parents. Adults need to disperse, mate and lay eggs, but larvae exist to store up energy and not much else. In other words, insect larvae have one job: to eat.

Protein-rich insect larvae (larvae rhymes with Harvey) have a challenge then. They need to eat to store up energy, but without wings and sometimes without even legs, they are easy targets. In order to elude their predators, they need creative survival strategies that allow them to eat without being eaten themselves.

One good way for a larva to avoid being eaten is to stay underground. Take the root weevil, for example. Adults feed on leaves, leaving tell-tale notches in lilacs and peonies, but their grub-like larvae eat plant roots and stay safely in the soil. Cutworms also hide in the soil, but they don’t eat roots. These fleshy caterpillars venture out of the ground at night to feed on plant stems and leaves, often stealthily cutting seedlings off at the soil line under the cover of darkness.

Some larvae cleverly create their own protected dining areas. Leaf roller caterpillars fold leaves and glue them together, then feed on the leaf tissue inside their shelter. Webworms and tent caterpillars surround entire branches with webbing so they can feed undisturbed beneath it.

Leaf miners have another ingenious way to hide and eat at the same time: rather than living on the leaves of a plant, these tiny caterpillars live inside them, protected in the space between the upper and lower layers of the leaf surface. Anyone who has tried to raise spinach, beets, or Swiss chard will recognize the tell-tale paths these larvae leave behind as they tunnel through the chlorophyll, hollowing out the leaves as they go.

For more stories like this, sent right to your inbox, sign up for our daily and weekly newsletters here.One of the safest places to feed if you are an insect larva is deep inside fruit where no predator can reach you. Codling moths are exceptionally good at this. Adult moths lay their eggs on developing pears and apples, crabapples, quince, and even walnuts. Larvae hatch and tunnel into the fruit for safety, eating towards the protein-rich seeds at the core.

If herbivorous larvae are doing damage to your plants when they eat, resist the temptation to reach for the chemicals. The same strategies larvae use to protect themselves from predators will protect them from insecticides, too. Indiscriminate topical treatments are not only ineffective against well-hidden larval pests, they can backfire. The beneficial predators who must forage and hunt in order to eat will be most exposed, allowing the pest population to grow unchecked.

Systemic insecticides were designed to outsmart insect larvae that can hide from topical sprays, but unfortunately, these pesticides do more harm than good. Instead of coating just the surface of a plant, systemics make the plant poisonous from the inside out, so that even the pollen grains in their flowers are contaminated. Systemic insecticides keep insect pests away, but inadvertently harm pollinators, predators, and other wildlife, too. They do so much damage to the ecosystem, in fact, that in 2026, the State of Washington will no longer allow systemics called neonicotinoids to be applied to outdoor ornamentals, trees, or turf without a license.

What is a gardener to do? Are plant-eating insect larvae unstoppable? They have very clever survival strategies, but take heart, because predaceous larvae and the adults they become have clever strategies for success, too. Here are some things you can do to give them the upper hand this season:

  • Choose pest-resistant plant varieties such as native plants
  • Keep your plants properly watered, since stressed plants are more vulnerable
  • Avoid over-fertilizing, as new growth can attract pests
  • Rotate crops to break pest life cycles
  • Cover leafy vegetables with garden mesh
  • Remove unwanted insects and cut out infested vegetation and debris
  • Prune to allow air and light as well as predator access
  • Work with predators instead of against them by keeping your yard chemical-free

Weekly Plant Clinic moving to Wenatchee library

The WSU Chelan-Douglas Master Gardener Program’s in-person Plant Clinic will resume weekly in-person clinic hours starting Monday, Feb. 24. The Plant Clinic will be open 1 to 4 p.m. every Monday in the Sagebrush Meeting Room at the Wenatchee Public Library, 310 Douglas St. The clinic will not operate on Monday holidays when the library is closed.

The clinic offers a chance for community members to seek answers about plant and garden issues. The Master Gardener diagnosis team is available to help identify problems with plants and garden pests and recommend solutions for maintaining healthy plants and managing pests. Please bring a sample, photos, and as much information as you can with you to your clinic visit.

You can also email your questions to askamastergardener@chelandouglasmg.org. Include your name and phone number in the email so a diagnostician can contact you if they need additional information related to your question.

More information about Plant Clinic services is available at bit.ly/mgplantclinic or by calling the WSU Chelan County Extension office at 509-667-6540.

— Marco Martinez, WSU Master Gardeners