Wednesday, August 31, 2016

More Insects From Sunflowers

My last post was devoted to the diversity of insects that find sunflowers (Helianthus spp.) irresistible thanks to the plant's extrafloral nectaries that provide nourishment for a host of wasps, bees, and other insects. Today, let's look at insects that feed on sunflower buds, leaves, stems, and roots. In stands of native sunflowers, these phytophagous (plant-eating) insects are a natural part of the ecosystem; but where commercial sunflower is cultivated for seeds and oil, those species can be pests.

Dectes texanus, 16 mm

Some of the most conspicuous sunflower feeders are beetles. The longhorned beetle Dectes texanus is damaging to sunflower in the larval stage. The female beetle lays her eggs in leaf petioles (the short stalk that attaches the leaf to the stem). The larva that hatches from each egg feeds inside the petiole, then moves down the inside of the main stem, eventually reaching the base of the plant. There, it girdles the inside of the stem and moves below this belt of death to insulate itself for the winter. It packs its own fibrous poop around itself and pupates. An adult beetle emerges the following summer.

Mecas pergrata, 6-12 mm

Mecas pergrata is another longhorned stem- and root-borer that exploits many plants in the sunflower family (Asteraceae).

Sunflower Beetle, 6-12 mm

Sunflower Beetle, Zygogramma exclamationis, is a leaf beetle that feeds on sunflower as an adult and a larva. The adults emerge from hibernation in late spring or early summer, coinciding with the sprouting of sunflower seedlings. The beetles feed on the young leaves. The beetles feed during the day, but their larval offspring feed at night, gathering in small groups among the bracts of flower buds in daylight. There is one generation per year, with adults emerging from the pupa stage in the soil in late summer. They feed briefly before returning to the soil to overwinter.

Pale-striped Flea Beetle, 3-4 mm

The Palestriped Flea Beetle, Systena blanda, is another kind of leaf beetle (family Chrysomelidae), and very small. This species has a wide range of host plants, many of them crops, including sunflower. The adult beetles overwinter, emerging in late spring and doing the most damage to the leaves of young sunflowers. They leave lace-like patterns of injury in their wake. The role of the larval stage in sunflowers is unknown, and perhaps they feed on a different plant.

Sunflower Root Weevil, 6 mm

Weevils, family Curculionidae, are beetles, too, and a whole suite of species is associated with sunflowers. The Sunflower Root Weevil, Baris strenua, feeds on the roots as a larva, and on the leaves as an adult beetle. The adults gnaw holes in the foliage in morning and late afternoon; but they move to the roots near the soil surface to create callous tissue into which the female deposits roughly three eggs at a time. The feeding activity of the larvae that hatch usually results in wilting of the plant due to dehydration. By autumn, each larva has created a soil capsule in which it will pupate. An adult beetle emerges the following year.

Sunflower Stem Weevil, 4-5 mm (generously)

Sunflower Stem Weevil, Cylindrocopturus adspersus, can be seen on the stems of sunflower plants, but they bear a strong resemblance to plant debris and are easily overlooked. Eggs are laid in the stem, and the larvae that hatch bore downward, reaching maturity at about the time they near the base of the plant. They hollow out chambers in the pith in which they will pupate the following year, usually in June.

Red Sunflower Seed Weevil, 2.5-3 mm

The Red Sunflower Seed Weevil, Smicronyx fulvus, is covered in rust-colored scales that rub off as the insect ages. The adults occur in late June and early July, feeding mostly on buds, then pollen once the flowers open. Eggs are laid internally in developing seeds, from the edge of the flower disc inward. Each seed usually feeds one larva, which consumes about one-third of the seed before exiting through a hole it chews, and plummeting to the ground and burrowing beneath the surface. Pupation occurs in the soil the following June or July.

Gray Sunflower Seed Weevil, 3.6 mm

Gray Sunflower Seed Weevil, Smicronyx sordidus, follows a similar life cycle as the Red Sunflower Seed Weevil, except that females deposit eggs externally on developing seeds while the flower is bud is still closed. Feeding by the larva results in an enlarged seed, clearly protruding above surrounding, unaffected seeds.

Sunflower Head-clipping Weevil, 8 mm

The Sunflower Head-clipping Weevil, Haplorhynchites aeneus, belongs to the family Attelabidae rather than Curculionidae. Adults of this species emerge in mid-summer, females feeding on pollen and nectar. Each female prepares for egg-laying by gnawing a perferation around the circumference of the sunflower stem, just below the flower head. She then deposits a single egg in the head. This eventually causes the head to fall off, and her larval offspring feeds in the head, eventually exiting into the soil to pupate.

Black Sunflower Stem Weevil, 3 mm

Black Sunflower Stem Weevil, Apion occidentale, is a member of the family Brentidae, or "primitive weevils." Adult beetles first appear in late spring or early summer, and feed on leaves and stems. Larvae feed internally on the pith of stems and the leaf petioles. Pupation occurs within the plant, adult beetles chewing their way to freedom in late July and August. Again the feed on foliage and stems but eventually move to the flower bracts by the end of summer. From there they enter the soil to overwinter.

Banded Sunflower Moth, 6 mm

Moths are another group of insects with many sunflower specialists. The Banded Sunflower Moth, Cochylis hospes, is a member of the leafroller moth family Tortricidae. The adult moths start showing up in mid-summer, but spend the day mostly away from sunflower plants. Females gravitate to the plants at twilight, laying eggs on the outside of bracts on the sunflower head. The caterpillars that hatch move onto the flower disk where they feed on seeds at all stages of maturity. Each larva eats five to seven seeds before leaving the plant for the soil where they spin a cocoon in which to pupate and overwinter. This moth is a certifiable pest to commercial sunflower growers.

Suleima baracana, 7.5-11 mm

Another tortricid moth is Suleima baracana, the caterpillar of which bores in stems of the Common Sunflower (Helianthus annuus). Look closely for it on the upper surface of leaves, and do not dismiss what you think is a bird turd. This moth looks exactly like the waste of a goldfinch, and appears at about the same time as that avian animal.

Sunflower Moth, 9 mm

Sunflower Moth, Homoeosoma electella, is a pyralid moth (family Pyralidae). The adult females flock to sunflower heads that are just beginning to open, and lay roughly 30 eggs per day on the heads. Young caterpillars feed on pollen and florets, but by the third instar (an instar is the interval between molts) they are tunneling into seeds. They also spin silk webbing over the flower head that becomes littered with caterpillar poop (frass). Mature larvae that have finished feeding then descend the plant to the ground where they spin silk cocoons and spend the winter before pupating in spring.

Several species of cutworms (family Noctuidae) and other moths also affect sunflowers. Even the Painted Lady butterfly may feed on sunflowers as a caterpillar, though they are usually found on thistles.

Sunflower Receptacle Maggot fly, 10 mm

Flies, specifically true fruit flies in the family Tephritidae, make up the last contingent of sunflower consumers. The Sunflower Receptacle Maggot, Gymnocarena diffusa, is a pale, attractive insect with patterned wings. They feed on the extrafloral nectaries. Females begin laying eggs in mid-summer between the second and fourth layers of bracts on the sunflower head. The maggots that hatch bore into the head where they feed. When finished, they usually chew a hole in the head and drop to the ground where they dig more than six inches deep before pupating. Some larvae may pupate within the sunflower head.

Sunflower Seed Maggot fly, 6 mm

The Sunflower Seed Maggot, Neotephritis finalis, first appears around the fourth of July as an adult fly. The female lays her eggs around the corollas of partially-opened florets in the flower disk. The larvae feed within the undeveloped ovaries of the flowers, thereby reducing seed set. Two generations of flies are produced each season. The first generation passes the pupa stage in the flower head; the second generation overwinters in the pupa stage in the soil.

The diversity of insects associated with sunflowers gives you some idea of what most all plants are up against in terms of insect enemies and affiliates. Each part of the plant is a likely target for at least one insect species. We know collectively little about the insects hosted by plants that are of no economic value, so much has yet to be learned. Better get to work, my friends!

Sources: Knodel, Janet J., Laurence D. Charlet, and John Gavloski. 2015. "Integrated Pest Management of Sunflower Insect Pests in the Northern Great Plains," North Dakota State University Extension Service, publication E1457. 20 pp.
"Insects," National Sunflower Association.
"Facts & Information on Sunflower Pests," Kansas State University Department of Entomology.

Friday, August 26, 2016

Sunflower Extravaganza

Few plants in arid climates can compare to sunflowers (Helianthus spp.) in their attractiveness to insects. Notice I said "plants" instead of "flowers." That is because while the sunflower blossoms are a beacon to bees, many other kinds of insects find secretions from the buds, stems, and leaves to be irresistible, too.

It is actually the sunflower's phyllaries (the bracts forming the involucre or the head or inflorescence of a composite plant), and the base of leaves, where the extrafloral nectaries are located. They produce a sweet substance different from floral nectar that insects crave. The main function of extrafloral nectaries (EFNs) is strongly suspected to be a means of recruiting insects to defend the plant against herbivores. Indeed, ants are the primary visitors to sunflower ENFs, and they vigorously pursue and rout any and all competitors.

A fly, two kinds of spider wasps (Pompilidae), and an incoming sweat bee (male Lasioglossum sp. on right)

Ironically, ants are also "farmers" of aphids, scale insects, and treehoppers that produce their own sweet product called "honeydew." Ants tenderly stroke these other insects until a drop of liquid waste appears at the rear end of their aphid or 'hopper "cow," and the ants eagerly lap it up. The aphids, scales, and treehoppers naturally manufacture honeydew as a by-product of their feeding activities....on the sunflower plant.

Treehoppers (Publilia sp.) tended by ants (Formica sp.)

So, while the ants guard the extrafloral nectaries, they also guard some of the insects doing the plant harm. Apparently no ecological relationship is perfect, but given the abundance of sunflowers, this one seems to work out ok anyway.

Parenthesis Lady Beetle and an ever-present ant

Even lady beetles utilize the ENFs as a source of hydration and vital nutrients during the summer months when there is a significant dip in aphid populations. I have seen several species on sunflower while looking for wasps.

Sunflower predator fest. Clockwise: Soft-winged flower beetle (Collops sp.), ambush bug (Phymata sp.), and assassin bug (Sinea sp.)

Other predatory insects recognize the lure of sunflower ENFs, too. Ambush bugs, Phymata spp., occur in abundance, and their success is measured by the many limp-bodied moths, butterflies, bees, and wasps dangling from their short beaks, or flopped across leaves below them.

Ambush bug with mud dauber wasp prey

It is the wasps, though, that are most astounding in their sheer diversity. I have found almost every conceivable family of wasps visiting sunflowers, and a high degree of diversity within each of those families in many instances.

Tiny chalcid wasp, Trigonura sp.

From the most minute of parasitic Chalcidoidea (a "superfamily" that contains several families of wasps) to large spider wasps and mud daubers, they are all there.

Female velvet ant, Dasymutilla bioculata

Even female velvet ants, wingless wasps which one usually sees scurrying across the ground, will scale tall sunflowers to reach those EFNs. Male velvet ants are even more frequent visitors, of course, with their ability to fly.

Large ichneumon wasp

Some individual plants are indeed tall, surpassing six feet in height. Those are mostly the Common Sunflower, Helianthus annuus. Locally, we also have Prairie Sunflower, Helianthus petiolaris, which is usually shorter, with purplish stems instead of yellowish green, and smaller, darker leaves.

The density of sunflowers in a given area can be mind-boggling as well. They thrive in "disturbed" habitats with sandy soil, which qualifies them to take over most of the urbanized Front Range here. Despite that, insects are noticeably attracted to only a few individual plants. So, once I find an attractive plant swarming with insect life, I stand by and watch as various wasp species come and go.

Female Svastra obliqua

Not a fan of wasps? No worries, a wide variety of bees visit the flowers, especially bumble bees, longhorned bees, leafcutter bees, and various cuckoo bees. Some bees, like Svastra obliqua, are even sunflower specialists. Composite flowers in general are bee magnets, but the very large surface of sunflowers gives bees plenty of bang for their buck in pollen and nectar. Sunflowers also bloom continuously for many weeks, even months, like a seemingly endless fireworks display.

Blue-black spider wasp, Anoplius sp.

One could literally write a book about all the insect visitors to sunflowers. Hm-m-m, that gives me an idea.....Meanwhile, enjoy the spectacle yourself next time you are in sunflower country.

Solitary wasp, Saygorytes sp.

Sources: Hodek, Ivo, Helmut F. van Emden, and A. Honek. 2012. Ecology and Behaviour of the Ladybird Beetles. UK: John Wiley & Sons. 561 pp.
Keeler, Kathleen H. 1979. "Species With Extrafloral Nectaries in a Temperate Flora (Nebraska)," Prairie Naturalist 11(1): 33-38.
Mizell, Russell F. 2015. "Many Plants Have Extrafloral Nectaries Helpful to Beneficials," EDIS, Institute of Food and Agricultural Scienes (IFAS), and University of Florida Extension, Publication #ENY-709.
The Great Sunflower Project.

Male Prairie Yellowjacket, plus spider wasp and ant

Saturday, August 20, 2016

Don't Sweat 'em

During the heat of summer, we all perspire. Some insects find that bodily function irresistible. Among them are sweat bees, various flies, and even butterflies. It is believed that the salts, minerals, and other compounds in our sweat are necessary for these insects, and difficult to find elsewhere. While you might assume that any insect landing on you intends to bite or sting, rest assured these insects are harmless.

Female sweat bee, Halictus rubicundus

Solitary and semi-social bees in the family Halictidae are collectively known as "sweat bees" because of their habit of lapping up human sweat with their short "tongues." They may tickle at most, but if you smack one absent-mindedly, it may indeed sting if it is a female bee. Male bees lack stingers.

Two different sweat bees, both Lasioglossum species

Sweat bees come in a variety of sizes and colors, from miniscule brassy Lasioglossum species to brilliant metallic Agapostemon species (and related genera). Members of the genus Halictus are medium-sized and brown or blackish with white bands across the abdomen. Nearly all species nest in the soil, each female excavating her own burrow.

Female sweat bee, Agapostemon sp.

Compounding the problem of recognizing the different insects that seek out your sweat is the fact that many flies in the family Syrphidae are wrongly called "sweat bees" in casual and regional language. Syrphid flies are more properly called "flower flies" here in the U.S. and Canada, and "hover flies" in Europe.

Tiny Toxomerus syrphid flies are often mistaken for sweat bees

Like bees, they can be important pollinators of flowers, but it is in their youth that they are most beneficial. The larvae of many flower flies prey on aphids, which are major crop and garden pests. Thus, the more syrphid flies, the better, even if they do want to drink your perspiration.

Unidentified syrphid fly on my arm, lapping sweat

Plenty of other flies, mostly blow flies (family Calliphoridae), and flesh flies (family Sarcophagidae), will land on us, too. Even some tachinid flies (Tachinidae) will wander around on bare hands and arms. They may not all be there for moisture or salts.

Tachinid fly using me as a lookout post

Some of these flies may be males that are simply using us as convenient perches from which to defend their territory. They will periodically fly off to chase away competing males, or pursue passing females.

Some butterflies are well-known for requiring certain minerals to complete their life cycle. Usually, male butterflies congregate around mud puddles, puddles of urine or piles of scat left by mammals, or even rotting carcasses, where they obtain nutrients that they will pass to females during mating.

Hackberry Emperor butterfly getting salts from animal dung instead of sweat

Males with a higher mineral content are more desirable to females, though how this is determined remains something of a mystery. She puts the transferred chemicals to good use in producing her eggs.

Occasionally, some butterflies will use us as substitutes for their usual mineral resources. I once had a Hackberry Emperor butterfly land on my toe while I was sunbathing in a park in Cincinnati. I had another land right on my sunglasses in a different location in Ohio, but he viewed me as a convenient perch from which to defend his territory.

Female Lasioglossum sweat bee with tongue extended, lapping sweat

Most research into the attractiveness of human sweat to insects has been directed at blood-feeding insects such as mosquitoes and other biting flies. Consequently, there is relatively little known, and much assumed, about the fascination non-biting "bugs" have with our skin pore excretions. One thing scientists can agree on? Don't sweat the sweat bees.

Tiny female Lasioglossum sweat bee on my fingernail

Source: Gibb, Timothy. 2015. "Do Not Confuse Hover Flies with Sweat Bees," Purdue Plant & Pest Diagnostic Laboratory, Purdue Extension, Purdue University.

Unidentified tachinid fly grooming itself on my arm

Tuesday, August 9, 2016

A Different Direction

Friends, I want to thank you for your continued patronage of this blog over the years. It has been, and continues to be, a privilege to serve you. At present, and for the foreseeable future, I find my life trending in different directions, and you will probably find fewer pieces of new content from now on. Please allow me to explain.

Most of the work I do to inform, educate, and fascinate is now done through social media, namely Facebook. I doubt I will ever indulge much in Twitter, or any of the other platforms, since I do not interact well with mobile devices (I am almost literally "all thumbs" on a tablet or smartphone). These platforms do, however, reflect something important that I must be cognizant of, and responsive to.

We are at a point where "instant gratification" is now possible through texting, internet messaging, and social media. The era of the blog may even be slowly coming to a close. No one wants to wait for a blog post when they are having a panic attack now over the spider crossing the kitchen floor. They can take a picture of it with their phone and send it over the airwaves to me or another expert immediately. This is the new 9-1-1, and 4-1-1, all wrapped up into one thing.

I honestly can't fault people for demanding information faster; and I would rather have it be me giving them a correct answer and advice than someone who does not know a brown recluse from a harmless wolf spider. Heck, I myself am "guilty" of using social media to get specimen identifications from authorities I trust. This is today's reality, and one must adapt or lose their impact and relevance.

Second, recent major expenses dictate that I must seek paying writing assignments and related work. I may even need to secure a traditional job outside the home, though I do not relish that prospect. Those who know me understand that I am not "greedy" or materialistic. Far from it. Still, even basic expenditures must be paid, and my income has increasingly stagnated. Doctor visits become more frequent as I age, with corresponding increases for medical bills. You get the idea.

Lastly, I have found increasing satisfaction from writing about topics completely unrelated to insects and spiders. So far, the outlet for this has been my other blog, Sense of Misplaced, but I am on the verge of seeking paying markets for personal essays and social commentary. I have loyal readers of that blog to thank for giving me the confidence and courage to believe that I can reach a far larger audience, and perhaps even influence cultural change and regulatory policies.

Our country, indeed the world, is in such a state of crisis that we need every voice to be heard. Every innovation, every idea, needs to gain an audience from those in places where those suggestions can be evaluated and implemented. I aim to be one of those voices for positive change, empathy, and leadership. I hope my audience here can transfer to my other blog, and on into mainstream media.

Meanwhile, I have enough posts in the Bug Eric archives that I feel it is still a sustainable resource. I continue to get positive, non-spam comments from new "recruits" delighted to find here the answer to that "mystery bug." I will still blog here periodically, at the very least to promote the work of others. Thank you again for your support.