Rotting vegetation is picture perfect for picture-winged flies in paradise: Picture-winged flies, Drosophilidae

 

Picture this picture-winged fly, which will soon deposit eggs on decomposing vegetation nearby.

 

Beautiful blossoms of the cannonball tree fall, rot, and become food for recyclers like the larvae of picture-winged flies.

In a previous episode we met strange gall-forming psyllids making their homes on leaves of the sacred ʻŌhiʻa tree, Metrosideros polymorpha. Once again, we escape the chilly confines of the DMV and return to the big island of Hawai’i to visit another intriguing family of insects, picture-winged flies, Drosophilidae. The Hawaiian archipelago formed and continues to grow as tectonic plates beneath the Pacific Ocean pass over a volcanic “hot spot.” This movement of the earth’s crust spawns enormous land masses that eventually emerge from the sea, the islands of Hawaii. For millions of years, this ongoing process has created new land, pristine habitat awaiting the arrival of plants and animals in what has been called an “evolutionary laboratory.” At some point in time eons ago, ancestral picture-winged flies, voyagers by an unknown conveyance, arrived on the islands and initiated a process of evolutionary adaptation exploiting the bountiful resources and diverse climatic regimes found in this tropical paradise. This unending process has resulted in almost 700 named species of drosophilids inhabiting the Hawaiian Islands, with another 300 or more yet to be described.

At the Hawai’i Tropical Bioreserve and Garden just north of Hilo, strange cannonball trees produce fragrant flowers along the length of their trunk. After visitations by pollinators, they rain to the ground and provide a rich source of nutrients for decomposers. Picture-winged flies swarm over the rotting blossoms and rest on vegetation before depositing eggs in the organic stew. Maggots like this one slithering across a leaf are important recyclers of organic matter. Hawaii’s diversity of plants, habitats, and isolation help generate roughly a quarter of all known drosophilid species worldwide.

Can you guess how the strange cannonball tree got its name?

While visiting the spectacular Tropical Bioreserve and Garden on Hawai’i, we had the opportunity to get up close and personal with one of the many species of drosophilids on the island. Along a forested path in the garden grows a remarkable, bizarre cannonball tree, Couroupita guianensis. This native of Central and South America is often found in botanical gardens around the world by virtue of its stunning blossoms and cannonball-shaped fruit. Trunks of the cannonball tree are festooned with extremely fragrant blossoms and woody round fruits, a stunning presentation of flowers and fruit. When blossoms complete their task of attracting pollinators, they tumble to earth and create a thick slimy carpet of decaying organic matter beneath the cannonball tree, a perfect nursery for developing larvae of drosophilid flies. As I crouched in the stinky goo to photograph some maggots, drosophilid flies swarmed around the vegetation beneath the tree. My efforts were rewarded when I discovered fly larvae slithering across the surfaces of decaying blossoms. Lucky me.

Ah, but all is not rosy for the drosophilid flies in Hawai’i. It turns out that the invasive western yellow jacket we met a few weeks ago finds drosophilids delectable. This predatory rascal is responsible for population collapses of many species of picture-winged flies since the yellow jacket arrived in the Hawaiian Islands. Let’s hope its presence doesn’t seriously disrupt the course of evolution of picture-winged flies and other creatures in this unique evolutionary laboratory.    Hawaiian

Acknowledgements

We thank Dan Gruner for stimulating discussions about the ecology of Hawaiian flora and fauna and Paula Shrewsbury for images used in this episode. The great articles “Sexual Selection and Speciation in Hawaiian Drosophila” by Christine R. B. Boake and “Hawaiian Drosophila as an Evolutionary Model Clade: Days of Future Past” by Patrick O’Grady and Rob DeSalle were used as references for this episode. We also thank the wonderful staff of the Hawai’i Tropical Bioreserve and Garden for creating a great location to observe and enjoy picture-winged flies and tropical plants.

On the prowl to paralyze pests here in the DMV: Four-toothed mason wasps, Monobia quadridens

 

Mountain mint, Pycnanthemum, is a delightful native plant and super attractor for many pollinators, including caterpillar-hunting, four-toothed mason wasps.

 

Last week we met a handsome wasp inspecting galleries in wooden posts at the visitor center in Volcano National Park on the big island of Hawai’i. The keyhole wasp, Pachodynerus nasidens, belongs to a subfamily of cosmopolitan vespid wasps called the Eumeninae, commonly called potter and mason wasps. As we learned last week, keyhole wasps use galleries abandoned by other insects or human-made tubes and hollows as nurseries to raise their brood. Now let’s travel a few thousand miles east back to the DMV to visit another member of the Eumeninae.

Several years ago, an eagle-eyed Master Gardener made an inquiry regarding black and white wasps poking around her mason bee colony. My gardener friend wondered about the identity and intent of these winged wonders. Were these wasps nefarious ruffians out to eat mason bee babies and pillage their pollen cakes? You may recall meeting hard working mason bees in a previous episode of Bug of the Week and seeing photographs of hollow cardboard tubes and holes drilled in wood used to accommodate these industrious early season pollinators. Mason bees are not the only members of the bee and wasp clan that have evolved to take advantage of vacant galleries in wood. These hollow chambers excavated by wood-boring bees like carpenter bees and round-headed beetle borers are used by several species of mason wasps as nurseries to raise their brood.

Nestled in tiny chambers made of mud, wasp larvae complete their development within a channel in my vinyl window frame.

As adults, mason wasps provide two important ecosystem services, one of pollination as they seek nectar and pollen as sources of food, and another as biological control of plant-eating caterpillars. Unlike the larvae of mason bees that consume pollen cakes supplied by their mothers, mason wasps consume living but paralyzed caterpillars. Prior to the hunt for caterpillar prey, the female mason wasp deposits her egg in the chamber where caterpillars will be stored. She then hunts for prey on flowers, foliage, vegetables, and fruit. Like potter wasps we met in a previous episode of Bug of the Week, female mason wasps use a potent venom to paralyze their pray. Sometimes as many as 19 caterpillars are captured, paralyzed, and used to provision the cell where an egg awaits. Once a sufficient number of prey has been captured, the chamber is sealed with a plug of mud or sand particles. In a remarkable display of gender control, the female wasp is able to lay either a male or a female egg. Due to the shorter developmental time of the male offspring, male eggs are usually placed near the opening of the gallery. Female eggs are placed deeper within the gallery. In this way faster developing males avoid trying to climb over, around, or bore through their sisters on the way out of the nursery.

Mountain mint looks like a super food for mason wasps as they carbo-load in preparation to search for caterpillars. Watch as this female sips nectar from several blossoms before the hunt. Natural holes made in wood by other insects and human-made holes drilled in logs for mason bees make great nurseries for mason wasps. A little tickle with a wisp of wood brings a female out of her nursery. A quick look around reveals nothing amiss and back she goes into the gallery to resume her work. To my surprise, a weep-hole made in the vinyl frame of my living room window makes a great nursery for a mason wasp. After provisioning galleries with paralyzed caterpillars to feed their young, mothers gather balls of mud which will be used to seal the nursery chambers. Using jaws and patience, a female makes a beautiful mudball. With the mudball complete and cradled beneath her legs, she flies back to her nursery. It takes several loads of mud to seal the gallery completely. Here a mother puts the final touches on her handiwork. A solid coat of mud plaster helps prevent enemies from attacking and killing her developing brood. 

Spotted horsemint, Monarda, is another gorgeous native perennial highly attractive to many beneficial wasps, including four-toothed mason wasps.

So, when you see these magnificent black and white wasps hovering around mason bee colonies, fear not, these are highly beneficial mason wasps looking for an empty apartment as a nursery to raise their brood. They are part of Mother Nature’s hit squad helping to reduce damage caused by caterpillars in our gardens and landscapes. You can make them part of your pest management team by providing them with critical nectar and pollen sources such as gorgeous native mountain mint and spotted horse mint.

Acknowledgements

The wonderful references “Trap nesting wasps and bees: Life histories, nests, and associates” by Karl Krombein and “The Cocooning Habit of the Wasp Monobia quadridens” by Phil Rau were consulted to prepare this episode.  

Gulf fritillaries wish you a Happy New Year from their new home in Hawai’i: Gulf Fritillary, Agraulis vanillae

 

The gorgeous Gulf Fritillary butterfly is an exotic visitor welcomed by many on the islands of Hawai’i.

 

This week Bug of the Week returns to some of the newest land on our planet, the Big Island of Hawai’i, to meet another beautiful immigrant to this tropical paradise. Over the holidays we learned that Monarch butterflies arrived on the Hawaiian Islands sometime after the introduction in the 1800’s of milkweeds, the key food source for their young. Like the Monarch, the Gulf Fritillary is also a super specialist that evolved to utilize members of the passion vine clan, Passiflora spp., as food for its young. When the edible passion fruit yellow granadilla, P. laurifolia, arrived in Hawai’i sometime before 1871, a door was opened for Gulf Fritillaries to colonize the big island and call it home. Records of Hawaiian butterflies prior to 1958 don’t list the Gulf Fritillary, but by 2002 these beauties were recorded on six islands of the Hawaiian archipelago. This broad ranging species takes up permanent residence from Argentina to the southern United States. During summer, peregrinations take it as far north as San Francisco on the west coast and New Jersey on the east coast, but in autumn this vagabond travels south to the warm climes of the Floridian peninsula to spend the winter. 

Flowers of the passion vine are among the most magnificent in the plant world but some passion vines are invasive on the Hawaiian Islands.

Like other members of the longwing butterfly clan, larvae of this beauty consume leaves of passion fruit vine. The blossom of the passion fruit vine is one of the most gorgeous in the angiosperm world. Exotic flavors of the passion fruit are used around the world, adding zest to ice cream, cheesecake, and mixed drinks. Passion fruit is rich in vitamin C and lycopene and consuming this delicacy is said to sooth a queasy stomach, according to Andean lore. As a group, passion fruit plants are protected from most leaf-munching caterpillars and other vegan insects by a veritable witch’s brew of highly toxic chemicals including alkaloids, a family of toxins that includes strychnine and nicotine, and cyanogenic glycosides, chemicals that release cyanide upon entering the digestive tract of a caterpillar or human. However, the Gulf Fritillary and other members of its clan, including the zebra longwing we met in a previous episode, turned the tables on passion fruit plants, bypassing the noxious defenses and feasting with impunity on their leaves. Some species of longwings sequester cyanogenic glycosides from their food and others manufacture these compounds on their own, presumably for defense. The striking orange and black coloration of the Gulf fritillary warns vertebrate predators not to mess with this beauty. In addition to any plant derived defenses, the gorgeous Gulf Fritillary has one more bit of chemical trickery to help keep predators at bay. Glands on the abdomen produce and release a concoction of complex esters when the adult butterfly is disturbed. This stinky defensive fluid dissuades predators such as birds from making a meal of these dazzling butterflies. 

The introduction of passion vines to Hawaii in the 1800’s opened the door for pretty Gulf Fritillaries to colonize. In their new home butterflies sip nectar from a wide variety of flowering plants. Females deposit eggs on leaves of passion vines and caterpillars consume leaves to obtain nutrients for growth and defensive compounds for protection from predators. Caterpillars often move from vines to pupate and their chrysalises can be found on human-made objects. While some species of passion vines are considered invasive on the Hawaiian Islands, Gulf Fritillaries are gorgeous colonists enjoyed by islanders. 

But the beautiful Gulf Fritillary is not all about noxious chemicals and defense. Oh no, observations of mating rituals of these beauties in the Norfolk Botanical Garden some years ago revealed romance afoot where a mating pair of butterflies engaged in a quixotic duet along a footpath. Many male butterflies, including Gulf Fritillaries, have a clever trick for winning the affections of would be mates. At the tip of his abdomen, the Gulf Fritillary has small bristles called hair pencils. The male uses his hair pencils to distribute aphrodisiac pheromones on the antennae of a potential mate. Courtship pheromones are released by the male over the female while both are in flight. These pheromones calm the female’s innate escape response and upon landing the male may hover over the female dusting her with more pheromones. The resulting romantic swoon induced by the pheromone allows the male to approach his mate and, well, shall we say, fulfill the biological imperative of procreation. Beauty, danger, and romance brought to a tropical paradise by airborne voyagers, who could ask for anything more of a butterfly? 

Bug of the Week wishes you a joyous New Year! 

Acknowledgements 

References used in the preparation of this Bug of the Week include ‘Caterpillars of Eastern North America” by David L. Wagner; “Coevolution of Animals and Plants” by Lawrence Gilbert and Peter Raven; “Gulf Fritillary Butterfly, Agraulis vanillae (Linnaeus) (Insecta: Lepidoptera: Nymphalidae)” by Jaret C. Daniels; “Novel chemistry of abdominal defensive glands of nymphalid butterfly Agraulis vanilla” by Gary N. Ross,  Henry M. Fales, Helen A. Lloyd, Tappey Jones, Edward A. Sokoloski, Kimberly Marshall-Batty, and Murray S. Blum; “Insects of Hawaii: A Manual of the Insects of the Hawaiian Islands, including an Enumeration of the Species and Notes on their Origin” by Elwood Zimmerman; and “Hawaiian Terrestrial Arthropod Checklist, Fourth Edition” by Gordon M. Nishida. We thank Dr. Dan Gruner for stimulating discussions about the ecology of Hawaiian flora and fauna and Dr. Paula Shrewsbury for images used in this episode.