Friday, September 16, 2016

A Beetle Mimicry Complex

This week, on one of my daily walks around our Colorado Springs neighborhood, I encountered a beetle on the sidewalk that gave me reason to pause. I initially dismissed it as a species of soldier beetle that is extremely abundant at this time of year, but something looked a little "off." Sure enough, it was something else; and that got me thinking about mimicry among all these beetles.

Blister beetle, Epicauta stuarti

The beetle on the sidewalk turned out to be a blister beetle, Epicauta stuarti, a species I had not seen before. Blister beetles, family Meloidae, are well known for containing high concentrations of the potent, irritating chemical cantharidin. Blister beetles exude the chemical in liquid form from leg joints and from between other body segments if the insect is squeezed or crushed. The chemical goo can raise painful, scarring blisters on sensitive skin; it can be fatal if ingested.

Ironically, many, if not most, blister beetles don't advertise their toxicity with bright "warning colors." Epicauta stuarti is one that does, but the interesting part is that its pattern of black and orange is very similar to that of our two common autumn soldier beetles. Soldier beetles are in the family Cantharidae, and they also have chemical defenses, which they secrete from abdominal glands. The Colorado Soldier Beetle, Chauliognathus basalis, is common on the plains. Its close relative, C. deceptus, replaces it in the foothills and mountains.

Colorado Soldier Beetle

This kind of shared color pattern that reinforces predator deterrence is called Müllerian mimicry. Both animals can back up their colorful advertisement of toxicity with actual chemical weaponry. This is a very interesting example of mimicry, but it doesn't end here. Other local beetles have jumped on the bandwagon.

End Band Net-wing Beetle, Calopteron terminale

Also appearing at this time of year is the End Band Net-wing beetle, Calopteron terminale. They generally occur in far fewer numbers than the soldier beetles, but can be mistaken for them with just a passing glance. It is widely assumed that net-winged beetles (family Lycidae) are distasteful to predators, because they have colorful patterns in many cases. Whether this has been proven I do not know.

Net-winged beetles may exaggerate the effect of their wardrobe by raising and lowering their wing covers (elytra) in a unique display. As adults, they feed on nectar, and the "honeydew" secreted by aphids and related insects as a sweet liquid waste product. Larvae of netwing beetles feed on fungi or metabolic products of fungi. Whether this diet can be converted into toxic compounds is debatable.

Longhorned beetle, Crossidius discoideus

While the jury may still be out on whether net-winged beetles are indeed toxic, there is no question that yet another mimic in this complex is pulling one over on predators. The longhorned beetle Crossidius discoideus fools us into thinking it is dangerous to eat by mimicking the pattern of the solider beetles. It can even be found on the same flowers as the soldier beetles and is difficult to easily separate from them, except for its long antennae. This brand of mimicry is called Batesian Mimicry, whereby a harmless animal masquerades as a dangerous one.

Crossidius discoideus has no common English name. As a larva, it bores in the root crowns of Broom Snakeweed, Gutierrezia sarothrae, or Jimmyweed (Isocoma spp.). The adults feed on flower pollen and nectar. Broom Snakeweed is also where the blister beetles hang out, so I may have to look more thoroughly for them now.

Longhorned beetle, Batyle suturalis

Yet another kind of longhorned beetle, Batyle suturalis, appears just before the populations of soldier beetles explode. Is it, too, taking advantage of a similar color pattern to gain "cover" from predators? What I would like to know is which of the truly toxic beetles started this whole complex. The blister beetle? The solider beetles? We will likely never know, and that is part of the appeal of entomology. It is an endlessly curious endeavor, seeking the answers to more puzzles than mankind will ever unravel.

Saturday, September 3, 2016

Do Insects Feel Pain? A Revealing Question

At some point in their career, every entomologist will be asked the question "do insects feel pain?" A surprising amount of research has gone into answering that question or, in some instances, unrelated research has provided insight into that query. My answer to that question has more to do with the person asking it, and as far as I know, that is a unique response.

Questioning the capacity for insects to feel pain says more about the one who intends to inflict it.

As one who interacts with the public more than many entomologists, it has become evident that while some people have no qualms about ending the life of an insect, even advocating extremely inhumane techniques ("Kill it with fire!" is a common reply to someone else's social media request to identify a household insect), there is an increasing tolerance for insects, even in the home. If the creature is unwelcome, there is now often a plea for a non-lethal means of dealing with the uninvited arthropod.

The flipside of this more empathetic response to "bugs" is the question of whether insects feel pain. The obvious, hoped-for answer is "no, they don't." The person asking is then relieved of guilt for harming or killing any insect in the past, present, and future. So, while the new trend is for more people, especially women, to seek humane methods of insect control, many people still look for examples of how insects do not deserve empathy and compassion as a way to vindicate their own behavior towards other organisms.

The bottom line in the question of whether insects feel pain is thus the unspoken question of whether killing insects and spiders falls into the category of cruelty to animals. Legally, it would be difficult to argue that insects, being animals, are exempt from that crime. Obviously, this is not the case, and I do not see that implied public consensus changing anytime soon. Swatting a mosquito could be an act of "self-defense," though, considering the atrocious diseases that those biting flies can transmit.

Ok, so you want a scientific answer? Most entomologists I know resort to the short answer that insects do not have "pain receptors" like higher animals. This means they have no nerve cells devoted to the perception of pain. Insects can sense heat and cold, for example, and various chemical and tactile stimuli, but not pain as we would define it.

Is the wasp feeling no pain while being killed by the spider?

The fact that many insects, and other arthropods, willingly sacrifice limbs and other body parts in order to survive predator attacks is a testament to how apparently immune to pain they can be. A missing leg hardly slows down a grasshopper. Tattered wings rarely encumber a butterfly finishing its mission of mating and procreation.

As a colleague and fellow blogger noted in his own treatment of this question, another important aspect of physical pain is the emotional distress that comes with it. Ascribing human emotions to non-human organisms is known in the scientific community as "anthropomorphism," and is considered a big no-no when attempting to conduct unbiased research and observations. So ingrained is the concept of avoiding anthropomorphism that we now have to question whether the unemotional conclusions we draw in animal behavior studies are really the correct ones. The truth probably lies somewhere in the middle.

The fact that people are asking questions like this that leave open the possibility that insects and other arthropods are sentient beings is a hopeful sign, regardless if that belief is based in reality. We could certainly stand a little more empathy for other living things. Then again, look how we treat other members of our own species.

Source: Ballenger, Joe, 2016. "Do insects feel pain?," Ask an Entomologist.

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