Are 17-Year Periodical Cicadas Harmful to Fruit Trees?

Periodical cicadas, especially those with a 17-year life cycle, are among the most fascinating and unusual insects in North America. These cicadas emerge in large numbers after spending nearly two decades underground, creating a spectacle that captures public attention. However, for orchard owners and gardeners, the question often arises: Are 17-year periodical cicadas harmful to fruit trees? This article delves into the biology of periodical cicadas, their interaction with fruit trees, and whether they pose any significant threat to orchard health.

Understanding 17-Year Periodical Cicadas

Periodical cicadas belong to the genus Magicicada and are known for their synchronized mass emergences every 13 or 17 years. The 17-year cicadas are notably prominent in the eastern United States. These insects spend most of their lives underground as nymphs feeding on xylem fluids from tree roots. When conditions mature, they emerge en masse as adults to mate and lay eggs before dying off.

Life Cycle Overview

• Nymph Stage: Lasts approximately 17 years underground.
• Emergence: Nymphs emerge synchronously in massive swarms over a few weeks.
• Adult Stage: Adults live for about 4-6 weeks, during which they mate and females lay eggs.
• Egg Laying: Females cut slits into small branches of trees to deposit eggs.

This mass emergence is a survival strategy known as predator satiation; by appearing in overwhelming numbers all at once, predators cannot consume them all, ensuring species survival.

How Do Periodical Cicadas Interact with Fruit Trees?

Fruit trees, such as apple, cherry, peach, and pear, are often planted in regions where periodical cicadas appear. The main concern centers around two biological behaviors of cicadas:

1. Feeding on Tree Roots (Nymphs): Underground nymphs tap into tree roots to obtain nutrients.
2. Egg Laying (Adults): Females use their ovipositors to cut slits into small twigs or branches where they deposit eggs.

Feeding Impact on Roots

While underground nymphs feed on xylem sap from roots, this activity is generally considered minimally harmful to mature trees. The roots provide a vast network of feeding sites, and the sap intake by cicada nymphs is relatively minor compared to the overall health of established fruit trees.

Research indicates that root feeding by periodical cicada nymphs does not significantly impair nutrient or water uptake in healthy trees. Seedlings and very young fruit trees might be more vulnerable due to their smaller root systems but even then, the damage tends to be minimal.

Egg-Laying Damage

The primary damage associated with periodical cicadas stems from egg-laying behavior:

• Adult females use sharp ovipositors to create slits or grooves in small branches and twigs, usually 1/4 inch wide, in which they lay clusters of eggs.
• This process severs vascular tissue in the branch causing it to weaken.
• The affected twigs often wilt and die off, a phenomenon called “flagging,” named for the characteristic yellowing or browning of affected tips.

In orchards and ornamental plantings, noticeable flagging can occur during emergence years. For established fruit trees, this twig dieback typically affects only smaller branches and does not kill major limbs or the whole tree.

Are 17-Year Periodical Cicadas Harmful to Fruit Trees?

Effects on Mature Fruit Trees

For mature fruit trees, those several years old and well-established, the effect of periodical cicada activity is generally minor and temporary:

• The extensive root systems of mature trees withstand nymph feeding without significant harm.
• Twig dieback caused by egg-laying leads mainly to localized loss of smaller branches but rarely affects structural integrity.
• Trees usually recover within one growing season as new shoots develop.
• There is no evidence that cicada emergence reduces fruit production or tree longevity significantly.

Effects on Young Trees

Young fruit trees and saplings are more susceptible because:

• Their root systems are smaller and nutrient reserves limited.
• Twig dieback removes a higher proportion of their canopy.

In some cases, heavy cicada egg-laying has led to enough damage to stunt growth temporarily or increase vulnerability to other stresses like drought or disease. However, outright tree death caused solely by cicadas is rare.

Crop Yield Considerations

While twig flagging can cause cosmetic damage, scientific studies show no consistent reduction in overall fruit yield following a periodical cicada emergence year. Healthy orchards that undergo routine care tend to bounce back quickly after the emergence event.

How Can Orchard Owners Manage Cicada Impact?

Because periodical cicada emergences happen predictably every 13 or 17 years, orchardists can plan accordingly:

Physical Protection

• Covering young trees with fine netting or mesh during peak emergence periods can prevent adults from accessing branches for egg-laying.
• This approach works best for nursery stock or recently planted saplings.

Pruning Strategies

• Prune out flagging twigs soon after emergence to minimize stress on the tree.
• Remove and destroy pruned material away from the orchard to prevent unnecessary egg hatchlings nearby.

Avoiding Vulnerable Planting Times

• Plant young orchards either well before or shortly after a predicted emergence year so that vulnerable saplings avoid peak egg-laying periods.

Chemical Controls

• Pesticides targeting adult cicadas are rarely recommended due to:
• The brief adult lifespan limiting effective application windows.
• Large-scale swarm size making thorough coverage impractical.
• Potential negative impacts on beneficial insect populations.

Ecological Role of Periodical Cicadas

Despite concerns about potential damage, it’s important to recognize that periodical cicadas play vital ecological roles:

• Their emergences bring a massive influx of nutrients into forest ecosystems when adults die off en masse.
• Predators such as birds, mammals, and other insects rely heavily on cicada emergences for food supply surges.
• By pruning small branches during egg-laying, cicadas may indirectly stimulate tree growth through natural selective branch loss.

Thus, while they may be a nuisance during emergence years, periodical cicadas contribute positively to ecosystem health over time.

Conclusion

Are 17-year periodical cicadas harmful to fruit trees? The answer depends largely on tree age and management practices.

• For mature fruit trees, these cicadas typically cause little lasting harm beyond some localized twig dieback that does not affect overall tree health or fruit yield.
• For young or newly planted saplings, heavy egg-laying can cause stress and stunt growth but rarely results in death if proper care is taken.
• Effective management approaches include physical barriers for young trees and timely pruning efforts.

Overall, while periodical cicadas may appear intimidating due to their sheer numbers during emergence years, they do not represent a serious threat to well-maintained fruit orchards. Understanding their biology helps orchard owners prepare for emergence events with minimal disruption, allowing nature’s unique rhythms to continue alongside productive fruit cultivation.

References:

1. Williams KS & Simon C (1995). The ecology, behavior, and evolution of periodical cicadas. Annual Review of Entomology, 40:269-295.
2. White JA (1999). The effect of periodical cicada (Magicicada septendecim) egg-laying damage on black cherry (Prunus serotina) seedlings. Forest Ecology and Management, 113(2-3):145-151.
3. United States Department of Agriculture (USDA) Forest Service factsheets on Periodical Cicadas (Magicicada spp.).
4. Copenheaver CA & Williams KS (2006). Effects of periodic cicada (Magicicada spp.) emergence on growth of mature sweetgum (Liquidambar styraciflua) trees: implications for forest management. Forest Ecology and Management, 236(1-3):231-237.