Deck the halls with boughs of holly adorned with cheery red and green berries! Green is good for holly berry midge, Asphondylia ilicicola

 

What’s up with the green berries on the holly tree?

 

Decorating homes and gifts with tiny sprigs of holly leaves and berries dates back to the Roman holiday of Saturnalia, the festival honoring Saturn at the time of the winter solstice. Saturn, the god of agriculture, abundance, and renewal reassured Romans that the darkness of the winter season would be followed by yet another year of light, prosperity, and plenty. And as we decorate our homes and gifts with holly, Mother Nature’s bounty of beautiful bright red berries on the holly tree attract many fascinating feathered friends such as mocking birds, blue jays, and cardinals to a winter feast. The berries provide a nutritious meal and, in return, the birds distribute the holly to new places by depositing seeds in their droppings.

This tiny fly larva and an associated fungus have the power to turn a holly berry from red to green, thereby enhancing chances of its own survival.

Recently, while photographing a gorgeous native holly, I spotted several holly berries distinctly green rather than scarlet red. Inside these fruits were tiny yellow maggots, larvae of the holly berry midge. In the spring when hollies were in bloom, the adult holly berry midge, a small mosquito-like fly, deposited eggs into the developing fruit of holly. These eggs hatched into larvae that fed within the berry. During the past growing season, the maggots consumed tissue of the fleshy fruit. In winter, larval development slows, but when the warmth of spring returns, these maggots complete development and become pupae from which emerge small midges that mate and deposit eggs into the developing berries, thereby completing the cycle of life.

Inside the holly berry, tiny holly berry midge larvae consume juicy plant cells. At less than 2 mm in length it’s hard to tell which end is which. In this video the head end is to the left and the rear end is to the right. Next year tiny flies called midges will emerge from the berry.

Adult holly berry midges are small mosquito-like flies. Note the papery pupal case left behind on the holly berry after the midge emerges.

For a small maggot, life in a holly berry is precarious. Its fate is tied to a red berry that advertises, "eat me" and hungry birds and squirrels happily oblige. These frugivores could literally eat the holly berry midge out of house and home. However, the larva of the holly berry midge has a clever trick to lessen its risks of disappearing down the gullet of a bird along with its fruity home. Berries infested by holly berry midge fail to turn red like normal holly berries do. The midge and an associated fungus prevent formation of bright red pigments by the berry. Infested berries remain green all winter. Through a series of detailed observations, researchers found that green holly berries were much less likely to be eaten by squirrels and birds than red berries on the same tree. By preventing the berry from turning red, holly berry midge has found a way to avoid the attention of fruit eating critters, thereby enhancing its chances for survival. So, as you deck your halls with boughs of holly, should you spy a green berry, you will understand why green is good for the cunning holly berry midge.

Bug of the Week is taking a Holiday break and will see you again in the New Year. Get ready to meet some interesting insects from the oldest rainforest on the planet in 2024. Have a wonderful Holiday Season and a joyous New Year!

 

 

Acknowledgements

We thank John Davidson for providing the inspiration and images for this week’s episode. The interesting references “Managing Insects and Mites on Woody Landscape Plants: an IPM Approach” by John Davidson and Michael Raupp, and “Selective Avoidance by Vertebrate Frugivores of Green Holly Berries Infested with a Cecidomyiid Fly (Diptera: Cecidomyiidae)” by Vera Krischik, Eric S. McCloud and John A. Davidson were used to prepare this episode.

Deck the halls with boughs of holly - and maybe some leaves with the native holly leafminer, Phytomyza ilicicola

 

Oh no, these less-than-pretty snakelike galleries are the handiwork of the native holly leafminer.

 

Holly trees play a significant role in the beliefs and traditions of the season. To the Romans, hollies were the trees of the god Saturn and wreaths of holly were given as gifts during his holiday, Saturnalia. In Celtic legends, the evergreen hollies with their beautiful red berries announced the triumph of the Holly King during winter over the Oak King, who ruled the forest with his green leaves in summer. For Christians, the pointed leaves of holly are associated with the crown of thorns worn by Jesus and bright red holly berries symbolize drops of his blood. For a bug guy, this is the season to marvel at a pair of fascinating flies whose lives are intimately tied to our stunning native holly.

Adult holly leaf miners resemble small houseflies. The male is on the left and the female is on the right, a cute couple. Credit: John Davidson

On my neighbor's beautiful American holly, red fruits intermingle with deep green leaves. Some leaves have unusual sinuous trails on their surface. Within the trails are the larvae of small flies, the young of the native holly leafminer. Back in the warmth of spring the adult stage of native holly leafminer, a small black fly, pierced the holly leaf with a structure on the tip of its abdomen called an ovipositor. This egg-laying appendage was then used to deposit an egg through the tough leaf surface into the soft tissue beneath. Upon hatching, the tiny larva consumed nutritious cells of the holly leaf and snaked its way through the leaf, enlarging the trail as it grew. In the dead of winter the larva rests, but on warm days during winter and early spring, the leafminer will continue to feed until it completes development and forms a pupa in spring. Before the larva changes into a pupa, it cuts a small window in the surface of the leaf to enable the adult fly to escape.

See the tiny yellow leafminer larva near the tip of the forceps on the inside layer of leaf epidermis. As it feeds within the leaf, it creates a snake-like serpentine mine.

Feeding punctures on the leaf surface made by adult flies may cause leaves to curl.

The emergence of the adult fly is timed to coincide with the appearance of tender new holly leaves in spring. In addition to laying eggs, the female holly leafminer uses her sharp ovipositor to poke holes in the leaf's surface. These small holes exude droplets of sap thereby providing a source of food for the hungry female. Leaves with many feeding holes are often curled or puckered. A horticulturalist once told me that these holes were caused by holly leaves with sharp spines bumping into one another, but now we know differently. As you gather holly sprigs to decorate your home, don’t worry if a leaf or two bears the serpentine signature of the native holly leafminer. They will not emerge in your home.

Spoiler Alert: Get ready for one more story about a fascinating fly found on holly in next week’s episode. 

Acknowledgements

We thank John Davidson for providing the inspiration and images for this week’s episode. The interesting references “Population regulation of the native holly leafminer, Phytomyza ilicicola Loew (Diptera: Agromyzidae), on American holly” by Daniel A. Potter, and “Seasonal allocation of defense investment in Ilex opaca Ation and constraints on a specialist leafminer” by D.A. Potter and T.W. Kimmerer, and the book “Managing Insects and Mites on Woody Landscape Plants by John Davidson and Michael Raupp” were used to prepare this episode.

A mast year brings a bountiful harvest to acorn weevils, Curculio glandium

 

The acorns weevil’s proboscis is remarkable by any standard.

 

In forests and landscapes here in the DMV, exceptionally humongous crops of acorns were produced by several species of red and white oaks this autumn. These large acorn crops occur periodically and in many types of plants such uber-productive seasons are called mast years. The exact climatic conditions underlying a mast year are not yet fully understood, but what is well-known is the fact that eaters of acorns including small and large mammals such as chipmunks, squirrels, deer, and bears, and many species of birds such as turkeys, quail, blue jays, and woodpeckers enjoy an autumnal food bounty when oaks go into acorn overdrive. Do any insects take advantage of this bounty? You bet! Enter the amazing acorn weevil. 

Legless weevil larvae emerge from circular holes in acorns and enter the soil in advance of winter.

The backstory to this episode begins with Stephanie, collector of native plant seeds, who was on a mission to gather seeds of our native pin oak tree. Soon after the acorns were collected, dozens of creamy, white, legless grubs appeared in the bottom of the collecting bag. At first glance this seemed like some incarnation of spontaneous generation – the appearance of life from non-life. However, on closer inspection, tiny, perfectly circular holes were visible on the hulls of many of the acorns. This was the work of the acorn weevil. Acorn weevils are remarkable creatures noted for their exceptionally long snouts. At the tip of the snout, or proboscis, are jaws that a female weevil uses to cut a hole in the husk of the developing acorn while it is still attached to a branch in the treetop. Into this hole, she deposits eggs that hatch and release tiny grubs which eat the nutritious meat of the acorn. In autumn, when the acorns drop to the ground, fully grown larvae chew small holes in the husk to escape their oaken nursery. They enter the soil and burrow several inches underground to pupate. They may remain in the soil for several years before emerging as adults in spring, with the return of leaves to the oak and the production of a new crop of acorns. Weevils emerge from the soil and climb to the canopy of the tree to feed and deposit a new batch of eggs. 

Periodically oak trees produce amazing crops of acorns in seasons called mast years. In addition to many birds and mammals, beetles called acorn weevils take advantage of the bounty. Female weevils deposit eggs inside acorns which hatch into larvae called grubs. Grubs develop during summer and escape in autumn through exit holes and enter the soil to pupate. A year or more later they emerge as adults and using jaws at the tips of their ridiculously long snouts cut holes in acorns, where the next batch of eggs are laid.

To observe these remarkable insects first hand, simply go outdoors to your favorite oak and collect a batch of acorns. According to one account, if you place these acorns in a container such as a pitcher or cooking pot filled with several inches of water and the acorns sink, they are usually intact and unlikely to be infested. Acorns that float have airspace within and are likely to contain weevil grubs or other interesting bugs. Crack a few of these open and observe the grubs inside. If you are really ambitious and desire a glimpse of the bodacious adults, you might try placing infested acorns in a pot with several inches of soil. This will provide grubs with the necessary habitat to complete their circle of life. The pots can be placed outdoors to expose the grubs to natural conditions of temperature and rainfall. Cover the pot with a bit of netting and, who knows, in a few years you may actually capture some fantastic beetles with schnozzolas so enormous, they would make Jimmy Durante jealous, ha cha cha cha.  

Acknowledgements 

Bug of the Week gives special thanks to Stephanie for providing the specimens and inspiration for this week’s story. The interesting article “The overwintering biology of the acorn weevil, Curculio glandium, in southwestern Ontario” by Hiroko Udaka and Brent J Sinclair was consulted for this episode. 

To learn more about acorn weevils, please visit the following websites: 

https://www.uky.edu/Ag/Entomology/ythfacts/allyr/yf804.htm 

https://content.ces.ncsu.edu/acorn-weevil