Green lacewings (Chrysopidae) are beneficial insects found worldwide, inhabiting temperate and tropical climates in fields, gardens, forests, and swamps. These delicate-looking insects and their larvae are valuable allies in controlling various agricultural and garden pests. This article delves into the dietary habits of green lacewings, exploring the differences between the larval and adult stages and their significance in pest management.
Green Lacewing Identification
Adult green lacewings are soft-bodied insects with golden eyes and four membranous wings held rooflike over the body at rest. The wings and body are commonly green, providing camouflage in areas of dense vegetation. However, adults of some species are normally brown, grayish, or reddish, resembling coloration of most brown lacewings. Some normally green species can turn brown or reddish during late fall through early spring, such as the common Chrysoperla carnea. They are typically 1/2 to 3/4 of an inch in length with long, slender bodies, long, slender antennae, and distinct copper-colored eyes. Adults are active during the nighttime hours.
Green lacewing eggs are oblong and 1/16 inch (1.5 mm) or less in length. Each is laid on the end of a silken stalk attached to plants. These ant-proof eggs are laid near aphid colonies, but to avoid the attentions of the ants that tend them, they are positioned teetering on the tip of a long, extruded thread.
Larvae are elongate and flattened with distinct legs and resemble tiny alligators. The body is about 1/2 inch long or less and commonly cream, tan, or yellowish with lengthwise lines or rows of spots that are blackish, dark or light brown, or reddish. Larvae can be active during the day and night.
Pupae occur in a roundish cocoon about 1/8 to 1/4 inch (3-6 mm) in diameter. The curled body is commonly visible through the loosely woven, whitish silk.
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In comparison with brown lacewings, larvae of green lacewings are distinguished by a trumpetlike appendage (empodium) between the pair of tarsal claws on the end of the feet. The thoracic segments of green lacewing larvae are of approximately equal length; brown lacewing larvae appear to have a prominent neck because the first abdominal segment (prothorax) is elongated in comparison with the second and third segments with legs.
Larval Diet: Voracious Predators
Green lacewing larvae are predators with a voracious appetite for soft-bodied insects. They use their sharp mouthparts to impale prey and suck the body contents, injecting digestive juices into the body of the victim. In less than 90 seconds, a liquefied meal is ready to eat. Each green lacewing larva will devour 200 or more pests a week during their two to three weeks developmental period.
Their diet includes:
- Aphids
- Mites
- Flies
- Thrips
- Leafhoppers
- Caterpillars
- Insect eggs
- Mealy-bugs
- Psyllids
- Whiteflies
- Small caterpillars
- Spiders
Larvae are so effective at controlling pest populations that they are sold commercially and can be released in greenhouses and gardens in large quantities. Releases of second-instar larvae have proven to be successful for the control of the green peach aphid in peppers, tomato and eggplant.
Larvae of certain genera (e.g., Ceraeochrysa) cover their body with plant debris or prey remains, such as the cocoons (puparia) of male scales or flocculence (waxiness) of woolly aphids. Other species only sometimes cover their body with trash, such as Chrysopa quadripunctata when preying on woolly aphids. This covering may serve as a defense against predators, such as ants that tend and protect aphids from natural enemies.
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Adult Diet: Nectar, Pollen, and Honeydew
While some species of adult green lacewings are predaceous, most feed primarily on nectar, pollen, and honeydew. This feeding behavior plays an important role in the pollination of various plants, as they transfer pollen from one flower to another during feeding.
Preferred foods for adult green lacewings include:
- Pollen
- Honeydew
- Nectar
Adult green lacewings are beneficial in establishing a standing population for continued control of pests or for improved pollination. Since lacewing larvae are the predatory stage, introduce adults early in the growing season prior to when garden pest control is needed. Each female adult lacewing lays around 200 eggs in a lifetime.
Life Cycle and Development
Green lacewings develop though 4 stages: egg, larva, pupa, and adult. The adult female lays about 100 to 300 eggs during her several-week lifespan. All stages can occur throughout the year in locations without cold winters. Adults become less active and may stop laying eggs and change coloration during late fall through winter. Green lacewings commonly have several generations per year. Egg to adult development requires about 4 to 6 weeks when temperatures are warm.
Female green lacewings will typically deposit the egg close a food source for the emerging larvae, which can include any plant infested with aphids. Green lacewing eggs will typically metamorphize to the larvae stage anywhere between three and ten days, depending on the weather. The green lacewing remains in the larvae stage from two to three weeks, and several instars later, then larvae enter the chrysalis stage.
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Five days later, a fully-formed adult insect emerges from the chrysalis. Some species of green lacewings overwinter in the pre-pupa stage, while others can overwinter as adults.
Green Lacewings as Biological Control Agents
The green lacewing larva is elongated and light-colored with brown and grey stripes on the sides of the body. Green lacewing larvae have big appetites and use their large, sickle-shaped mouthparts to consume soft bodied insects. The larvae are so effective at controlling pest populations that they are sold commercially and can be released in greenhouses and gardens in large quantities. The use of lacewings to control arthropod pests have been reported for several crops, worldwide. For example, releases of second-instar larvae have proven to be successful for the control of the green peach aphid in peppers, tomato and eggplant. The efficiency of lacewings to control pests can be affected by many factors, including: pest type, distribution of the pest (e.g., within and among plants), weather, crop, and number of predators released, stage of predator released, and the predator/prey ratio. The efficiency of pest control can be increased in small scale production systems by manipulation of the environment (e.g., food supplement, attractants, and crop inter-planting), in which the predators are to be released. The use of green lacewings in greenhouses can be effective by using multiple or inundated releases. Green lacewing larvae or eggs of the predator can be released to control pests in greenhouses. However, if control is needed in a short period of time, the larval stage is the recommended stage to be released. Good to excellent control has been reported when the predator-prey ratio is between 1:3 to 1:5. For both field and greenhouse pest management, the use of green lacewings can be an effective component of IPM. Green lacewings have also been reported to have a degree of resistance to a number of insecticides.
To maximize the effectiveness of green lacewings as biological control agents, consider the following:
- Eradicate ants: Ants protect aphids from predators like lacewings because they feed on the honeydew produced by aphids.
- Release adults early: Introduce adult lacewings early in the growing season to establish a population before pest control is needed.
- Provide food supplements: Offer a mixture of honey or sugar and water as a food source for adult lacewings.
- Release rates: Rates vary based on pest pressure.