Month: July 2020

I really don’t have anything against beetles. In fact, beetles and I go back a long way as I studied many awesome leaf beetles in graduate school. However, butterflies, especially monarch butterflies, are a real delight and like many naturalists, I anxiously anticipate their return each year and celebrate their arrival. Two weeks ago the vanguard of what I hope will be a swarm of monarchs arrived and began poking around my milkweeds. Unfortunately, in advance of the monarchs, another hungry milkweed connoisseur moved into my butterfly weed patch well in advance of the monarchs. Milkweed leaf beetles are relatives of other members of the chrysomelid clan, a large group of beetles that includes dogbane leaf beetles, Colorado potato beetles, and three-lined potato beetles we met in previous episodes. Adults and larvae of this striking insect eat leaves of common and swamp milkweeds growing wild in meadows, and also butterfly weeds running rampant in my perennial beds. Adult beetles are voracious feeders and after colonizing my butterfly weed, they quickly removed large slices of leaves. Milkweed leaf protein is translated into batches of eggs inside the ovaries of females. About a week after eggs are laid, rotund orange beetle larvae hatch and graze night and day.

Tiny orange jellybean-like eggs on the leaves of my butterfly weed soon hatch and release rotund leaf beetle larvae intent on devouring milkweeds. Adult milkweed leaf beetles are large enough and apparently scary enough to displace small monarch caterpillars as they dine on milkweed leaves. Fortunately, butterfly weeds are prolific and there should be enough to go around for all of the insects that make a meal of milkweed.

One curious and somewhat disturbing habit of milkweed leaf beetle neonates is to go cannibalistic after hatching. Yes, some early hatchers perform the ultimate act of sibling rivalry and eat their unhatched brothers and sisters. Yikes! After starting life as meat eaters, the cannibals and their surviving siblings settle in to a vegan life style, consuming milkweed leaves before moving to the soil to pupate. In a few weeks, a fresh batch of adult beetles will emerge and initiate new conquests on my beleaguered butterfly weeds. As autumn approaches, the season’s last batch of adults fatten up on milkweed leaves before finding a protected refuge somewhere in my garden to spend the winter. As you can see, milkweed leaf beetles sport the same orange and black mien worn not only by the monarch, but also by milkweed tussock moths and milkweed bugs we visited in other episodes. This cabal of milkweed feeders has evolved the ability to thrive on milkweeds despite the presence of noxious heart poisons called cardiac glycosides found in the cells and sticky white sap of the milkweed plant. In some species like monarchs, these compounds are retained during the transformation of caterpillars into adult butterflies. Cardiac glycosides found in the wings of monarchs are known to cause severe digestive distress to avian predators. These compounds help protect monarchs from disappearing down the gullets of visually gifted predators like birds that regularly prey on caterpillars, butterflies, and beetles. Conspicuous orange and black colors worn by members of the milkweed gang serve as a reminder of a potentially nasty gastronomic misadventure to experienced birds and other predators that may have attempted to make a meal of a milkweed muncher. Fortunately for the monarch, butterfly weed is prolific and I hope there will be enough for everyone if and when the monarchs arrive in force.

Acknowledgements 

The delightful book “Secret Weapons” by Thomas and Maria Eisner and Melody Siegler, and the articles “Community-wide convergent evolution in insect adaptation to toxic cardenolides by substitutions in the Na,K-ATPase” by Susanne Dobler, Safaa Dalla, Vera Wagschal and Anurag A. Agrawal, and “Cannibalism and Kin Selection in Labidomera clivicollis (Coleoptera: Chrysomelidae)” by Kathleen R. Eickwort were used to prepare this episode.

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In previous episodes we visited sensational Asian giant hornets, a.k.a. murder hornets, and some of their look-alikes including European hornets and cicada killer wasps. Last week I received my first image of a male cicada killer and a somewhat panicked inquiry wondering if this might be the vanguard of dreaded murder hornets ready to invade the DMV. Relax, male cicada killers are harmless to humans but not so to dog day cicadas. This week, let’s learn a bit more about these awesome wasps from excerpts of an episode of Bug of the Week posted a couple of years ago. Cicada killers kill cicadas as a food source for their young. During the daytime, female cicada killers hunt prey in the treetops where dog day cicadas are found. Once captured and paralyzed, cicadas are interred in subterranean crypts. To see how female cicada killers roll, please check out this episode of Bug of the Week, “Cicadas beware, the ladies are in town: Female cicada killer, Sphecius speciosus”.

Although they appear fierce and perhaps even dangerous, male cicada killers pose no threat to humans or pets. Only females have a stinger, and try as he might, the male’s jaws and genitalia failed to puncture my skin. However, I have heard tales of females delivering a memorable defensive sting when inadvertently stepped on or trapped under knee or hand. Video credit: Paula Shrewsbury, UMD

Recently, in advance of the appearance of the ladies, two male cicada killers established territories about twenty feet apart in my flower bed. So began a fierce competition for dominance of space and, I suppose, eventual access to the babes soon to emerge from the earth. Each morning shortly after sunrise as the morning sun warms the land, two feisty males arrive at their respective perches, one on a short yew bush and the other on the nozzle of my garden hose. As you will see in the video, they are on high alert, frequently leaving their perch for a short flight. Not quite understanding the thinking of the wasp mind, I imagine these forays are designed to provoke a battle with the other hopeful suitor. Occasionally, these sorties extend far enough from the perch that one male will enter the territory of the other. This results in a remarkable battle complete with frenetic buzzing and males interlocked in flight. It appears much biting and kicking goes on as evidenced by the response of a cicada killer when I captured one and held it. Eventually one breaks away and skedaddles toward my neighbor’s lawn with the victor in hot pursuit. But the victory seems fleeting. Male cicada killers either have remarkably short memories or indefatigable egos as the aftermath of these vicious mêlées soon results in both males returning to their perches only to repeat the battle a short time later.

One perched on a shrub, the other perched on my garden hose. These two fellows are pumped and looking for a tussle.  Short forays from the perch sometimes result in spectacular aerial battles as each tries to lay claim to the territory where females will soon appear.  Video credit: M. J. Raupp

Perhaps one sunny morning only one of these fierce flyers will remain and the vanquished will have departed for less ardently defended turf in search of his own mate.  But for now, with coffee in hand, this is the best early morning bug show in my garden.     

Acknowledgements

For more information about cicada killers including videos of them in action, please visit Chuck Holliday’s magnificent cicada killer website, BIOLOGY OF CICADA KILLER WASPS.

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Spotted beebalm, scarlet beebalm, and wild bergamot, these members of the Monarda clan are some of my absolute favorite perennial landscape plants. Why? By providing rich nectar rewards, these delightful natives are magnets for an astounding array of beneficial animals ranging from hummingbirds and gold finches to butterflies, bumble bees, hover flies, and myriad predatory and parasitic wasps. I have watched the summer parade of interesting and beautiful insects visiting Monardas for hours over a cup of coffee on sunny summer mornings.

But every year, there is foul-play afoot in my flower beds. Sometime in the latter days of May and early days of June, just as the bergamot is prepping to bloom, developing flower buds and their attendant sepals become shredded and riddled with holes. Close examination of the buds reveal tiny black pellets lodged in the nooks and crannies of the flower heads. Now, to bug geeks, tiny black pellets usually are a sign of insect activity. Said pellets are actually the excrement, a.k.a. frass, of caterpillars feeding within the flower buds. Some further poking around the nascent blossoms revealed small creamy colored caterpillars hiding in the axils of sepals and at the bases of florets. While identification of small caterpillars presents a challenge even to seasoned entomologists, identification of adult moths and butterflies is way easier. A more extensive search of the bergamot patch revealed a rather pretty raspberry pyrausta moth, a member of the crambid moth clan. Crambid moths, also known as snout moths, are named for the elongated mouthparts protruding from the front of their head. Many bore into the stems of grasses and other monocots and some, such as the European corn borer and sod webworm, are serious agricultural and lawn pests. Just one or a few of these caterpillars feeding within a developing flower bud are sufficient to all but ruin its floral display.

Here is the dilemma. For many herbivores in my landscape, the death sentence is commuted under a live-and-let-live policy with the belief that even pests will become food for other insects or birds higher in the food web. However, in the case of the raspberry pyrausta, lack of intervention translates into few or no blossoms on Monardas and few or no resources for pollinators, predators, and parasitoids dependent on nectar and pollen for their activity and survival. So, in this case the caterpillars gotta go to make way for the beneficial insects. Ridding the blossoms of caterpillars is fairly easy to do. As flower heads begin to form in late spring and early summer watch out for holes in leaves, feeding damage to developing florets, and small black frass pellets accumulating in the axils of leaves and sepals. Carefully search the flower head and when you locate the caterpillar, simply crush it. If you don’t like touching insects, don a pair of rubber gloves and do the deed. Mechanical destruction of the pest is foolproof and works well in small patches.

While some blossoms on my bergamot look fine, many are ravaged. This culprit is a small caterpillar feeding in the flower head. Chewed florets, holes in leaves, silk, and pellets of frass are telltale signs of the caterpillar. Regular inspections and crushing caterpillars when you find them will help keep your blossoms looking fine.

For larger plantings, you could consider using an insecticide listed by the Organic Materials Review Institute (OMRI) for controlling caterpillars. These insecticides have been reviewed by scientists and approved for use in the production of organic food crops. Two of my favorites contain the active ingredient Bacillus thuringiensis kurstaki (Btk) or spinosad. Btk is derived from a common soil microbe and it works well on many species of caterpillars. If you grow milkweeds as a source of food for monarch caterpillars in your flower beds, take care not to spray Btk on your milkweed lest you poison any resident monarch larvae. Some brands of spinosad will also carry the OMRI stamp of approval and they work well on caterpillars. Spinosad is also a product of a soil microbe. This molecule attacks the nervous system of insects. But be careful with spinosad, as it is highly toxic to bees. If other plants in your garden are in bloom or are about to bloom avoid drift that might contact and harm charismatic pollinators. Use the same caution with Monarda. The pyrausta will be present in the early formation of flower buds but as florets form and mature, avoid using spinosad as bloom time approaches and certainly when flowers are in bloom. Many snout moths have multiple generations and in my experience the raspberry pyrausta is no exception. I have crushed several crops of caterpillars in the flower buds and just the other day, a few more adult moths dared to flit around my flower bed.

For a bug geek, watching the sunrise on a warm summer morning while sipping some coffee and squashing some caterpillars is not a bad way to start the day.  

Acknowledgements

We thank Dr. Shrewsbury for providing the inspiration for this episode as well as snapping some photos and crushing caterpillars to save the monardas from marauding caterpillars.

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One of the upsides of the ongoing COVID-19 pandemic is a notable increase of folks enjoying time outdoors walking, cycling, and visiting at social distances along neighborhood streets. One steamy morning last week as I circled the block, I noticed surprising numbers of rather large bees buzzing about mailboxes along the streets. Bees interested in postal delivery? A closer look told the tale. Let’s start with the mailbox. If your mailbox is like mine, it rests atop a wooden post some four feet or so above the ground. Over the years the post supporting my mailbox has become home to an occasional colony of carpenter bees. Year after year sometime in May the carpenter bees reliably return to the mailbox post. Males perform aerial battles for dominance of the mail box territory and their mates chew perfectly round holes in the mailbox post, entrances to brood chambers for their young. But in July, as carpenter bee activity wanes, activity around the mailbox post is supplanted by another type of bee. The aerial acrobats now performing near mailboxes are giant resin bees, exotic colonists from Asia first reported in the United States in North Carolina in 1994. In addition to their native Asian range that includes China, Japan, and South Korea, giant resin bees have been discovered in Italy, France, and Switzerland in Europe. In North America they range from Canada to Alabama in most states east of the Mississippi and have been reported in almost all counties in Maryland.  

Giant resin bees belong to a family of solitary bees known as Megachilidae and are kin to mason bees and leaf cutter bees we met in previous episodes. Like mason bees, each female bee is reproductively active and therefore dissimilar to social bees like honey bees and bumble bees that have a queen. Their presence near a mailbox post riddled with carpenter bee galleries is no mystery. Despite sporting powerful jaws, the potency of which I discovered after handling one, giant resin bees do not excavate galleries in wood. Their sharp jaws are simply not strong enough to do so. Instead, they rely on existing galleries to create a home for their brood. Abandoned galleries of carpenter bees provide perfect chambers to colonize and raise their young. While male giant resin bees spend time defending territories and chasing each other about, female bees gather plant resins to line the inside of the gallery. After each chamber is properly prepared, females collect pollen on fine hairs called scopa on the undersides of their abdomens, return to their galleries, and create pollen balls inside the brood chamber. Eggs are laid on the pollen balls, which serve as the food source for the developing larvae.

On my neighbor’s mailbox post a male giant resin bee arrives to stand guard. When not performing aerial antics, male giant resin bees can be found fanning their wings around co-opted carpenter bee galleries. Does he await the appearance of a lovely lady bee while shooing away other potential suitors?

The ecological impact of these nonnative bees is still largely unknown. They have been observed foraging on several imported plants from their native range including golden rain tree, Koelreuteria paniculata, glossy privet, Ligustrum lucidum, kudzu, Pueraria lobata, and Japanese pagoda tree, Sophora japonica. There is some concern that they may commandeer nesting sites of our native carpenter bees, but the true magnitude of this effect is still unknown. With the abundance of human made habitat for carpenter bees, there may be enough wood to go around for all wood-nesting bees. Who knows? Nonetheless, these goliaths of the solitary bee world are here to stay and they make an interesting study on a walk around the block on a warm summer morning.  

Acknowledgements 

We thank our gracious neighbors who allowed us to photograph giant resin bees on their mailbox post early one morning and our friends at Woodend Sanctuary for allowing us to film their giant resin bees. The interesting article “Invasive Megachile sculpturalis in Upstate New York” by Robert G. Laport and Robert L. Minckley was consulted in preparation of this episode.  Bee guru Sam Droege provided the fantastic image of a female giant resin bee featured in this episode.

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