Readers’ wildlife photos

August 8, 2022 • 8:15 am

Today’s piece comes from Athayde Tonhasca Júnior, whose captions and narrative are indented. Click on the photos to enlarge them.

The unloved ones

Thrips, also called thunder flies or thunder bugs, are small (most species are 1-3 mm long), slender insects. Their wings are fringed, a characteristic used to name their order: Thysanoptera, from the ancient Greek thysanos (tassel or fringe) and pteron (wing) – although not all species are winged. There are around 6,000 known species, mostly from tropical and temperate regions of the world.

An onion thrips (Thrips tabaci) on the left and a western flower thrips (Frankliniella occidentalis) (it’s ‘one thrips’ and ‘two thrips’) © Alton N. Sparks, Jr., Wikimedia Commons.

Thrips are not among the most cherished insects; if you search for them in the internet, the first pages are likely to include ‘how to get rid of’ in their titles. Indeed, many thrips species are pests of crops and vectors of plant viruses. They feed by puncturing tissue and sucking up plant juices, thus reducing yield, damaging commercial flowers and fruits, and often causing galls or leaf rolls. They are capable of parthenogenesis (reproducing without fertilisation), so in situations where natural enemies are scarce, such as in greenhouses, thrips populations may explode. Gardeners are familiar with flower thrips, which look like masses of dark specks scurrying over petals and buds. To add injury to insult, the little blighters can ‘bite’ (actually they jab with their mouthparts), causing mild skin irritation in some people.

A thrips on a finger © Daiju Azuma, Wikimedia Commons.

 A cluster of flower thrips © Laurence Mound, ThripsWiki.

But not all thrips are bad for us. Some species are predators of other pests such as scale insects and plant mites. And because so many of them hang around flowers, it has been long thought that there’s more to their story than pollen munching. Traditionally, thrips have not been considered to be relevant pollinators because they are small, poor fliers, and have no structures adapted to carry pollen. On the other hand, they do move from flower to flower with pollen attached to them, and their large numbers may compensate for small pollen loads. When Charles Darwin was busy with his plant reproduction experiments, he noticed he couldn’t exclude thrips from his net-enclosed flowers. He pondered whether these gate crashers were cross-pollinating plants he intended to be self-fertilized (Darwin, C. 1892. The effects of cross and self- fertilization in the vegetable kingdom).

A: Pollen grains attached to a thrips’ bristles (setae); B: a closer view of the pollen clinging to the abdomen of the thrips © Eliyahu et al., 2015. Journal of Pollination Ecology 16: 64–71.

It turns out that the more researchers look into it, the more they find evidence of thrips pollination, especially for plants previously identified as wind-pollinated. Species such as the common wilkiea (Wilkiea huegeliana) and the Red List species Brazilian walnut (Ocotea porosa) from the Australian and Brazilian rainforests, respectively, are thrips-pollinated; and possibly coffee (Coffea spp.), cacao (Theobroma cacao) and chili peppers (Capsicum spp.) are too, at least partially. Bearberry (Arctostaphyllos uva-ursi) and other heath or heather species (family Ericaceae), long assumed to self-fertilize, are pollinated to some degree by thrips, especially in high latitudes where other insects become scarce.

Elder or elderberry (Sambucus nigra) is another strong candidate for thrips pollination. Evidence comes from exclusion experiments – where thrips are kept off flowers and plant fertilization is then assessed – and from floral characteristics suitable for thrips such as compact inflorescences and powdery pollen. Elder grows in woodland, grassland, scrub, hedgerows, roadsides, brown sites, or any habitat with disturbed soils across most of Europe. If thrips pollination is confirmed, it would set this plant apart from other common members of the European flora.

Elder in flower, a haven for thrips © Willow, Wikimedia Commons.

Thrips pollination is relatively rare and poorly understood, but it has been going on at least since the Early Cretaceous (145 million years ago, give or take a few months). And it reminds us of some important points. Bees and flies may have the spotlight as far as pollination services go, but there are other players out there, even though we know very little about them and how they interact with each other. They often have conflicting roles – as destructive pests, biological control agents or pollinators – so we must be cautious when considering intervening. Nature is complicated.

Thrips are not liked, but they could do much worse on the empathy scale.

When people are asked to list their most feared or reviled animals, sharks are almost invariably mentioned; snakes, wolves and crocodiles are other popular bogeys. These choices reveal a sharp dissonance with the real world, because sharks account for some 80 unprovoked bites per year, with about ten deaths: lightning is about 50 times more deadly. Wild reptiles and mammals are slightly more dangerous, dispatching an estimated 75,000 souls annually.

We may have nightmares about big wild beasts, but most of us are unaware they are small fry when compared to some of the Grim Reaper’s most efficient agents: mosquitoes.

According to the World Health Organization, mosquito-borne diseases kill around 725,000 people a year, some 600,000 of them from malaria. Dengue, West Nile virus, yellow fever, zika, and many other pathogens and parasites transmitted by mosquitoes add to the vast numbers of people killed or debilitated, mostly children and the elderly in developing countries.

Fig. 6. Zika virus information © World Health Organization.

Considering the magnitude of suffering, let alone the economic impact of mosquito-borne diseases, nobody could be blamed for wishing mosquitoes to disappear from the face of the Earth. And with today’s knowledge and technology, a mosquito wipeout is not farfetched. Large-scale programs of genetic manipulation, male sterilization, bacterial infection or another technique could do the trick.

The question is, should we have a go at getting rid of mozzies?

There are more than 3,000 species of mosquitoes (family Culicidae), and most of them go about their lives feeding on nectar and other plant substances, never getting even close to humans or other animals. Only 200 or so feed on people, and a handful are responsible for the spread of diseases: mostly species from the genera Aedes, Anopheles and Culex.

So, eradication schemes would likely sweep away innocent bystanders, which comprise the majority of mosquitoes. And there could be consequences. Mosquito larvae and adults are food to dragonflies, tadpoles, some turtles and fish; adults are also eaten by bats and birds. In the Arctic tundra, the Biblical numbers of mosquitoes during summer are a significant menu item for migratory birds. But ecologists debate the importance of mosquitoes as a food source: some maintain that bats, fishes and birds would decline sharply, with reverberations along the food chain; others believe that mosquito eaters would adapt and switch easily to midges and other insects.

Mosquitoes are considered mostly nectar thieves, that is, they take nectar without transferring pollen between flowers. But as improbable as it sounds, some of the pesky creatures pollinate. The blunt-leaved orchid (Platanthera obtusata) and the Northern tubercled bog orchid (Platanthera flava) give off faint mixtures of scents that some Aedes mosquitoes find irresistible. When a mosquito sticks its head into these orchids’ flowers, it may come out with a pollinium (a bag of sticky pollen) glued to it. The pollinium can be almost as big as the mosquito’s head, and it’s surprising the reluctant pollinator is able to fly away. Both orchids are pollinated by moths as well, but mosquitoes seem to be their main pollinator.

Left and bottom right: male and female Aedes aegypti probing the flowers of a blunt-leaved orchid. Top right: A pollinium attached to the eye of a mosquito © Lahondère et al., 2019. bioRxiv, now published in PNAS 117: 708-716.

Other orchids are mosquito-pollinated, and probably several other plant types are too. Culex pipiens and related species contribute to pollen transfers for tansy (Tanacetum vulgare) and other members of the Asteraceae, and for the aptly named mosquito flower (Lopezia racemosa) and Spanish catchfly (Silene otites). Aedes spp. help pollinate the white mountain-avens (Dryas integrifolia).

The mosquito flower © Juan Carlos Fonseca Mata, Wikimedia Commons.

The Spanish catchfly © Stefan.lefnaer, Wikimedia Commons.

Evidence for mosquito pollination is often circumstantial but credible. Field collected specimens can be loaded with pollen grains, at levels comparable with moths and butterflies.

What would happen to those plants in a world without mosquitoes? It’s impossible to say. They could get by with the help of alternative pollinators or by self-pollinating, or they may go extinct. If we ever have the wherewithal to eliminate mosquitoes, we will need to ponder the balance between deliberate species extinctions and sparing millions of human beings and animals from death and sickness. The dilemma will keep many a moral philosopher awake at night.

17 thoughts on “Readers’ wildlife photos

  1. Thank you for some fascinating information here. And I love the name Thrip, which seems to perfectly describe these twisty flighty little things.

  2. A fascinating post as usual Athayde. By way of speculation about the impact of completely eliminating mosquitoes, I wonder if there could also be an impact in terms of the behaviour of their mammalian hosts? The impact of the reintroduction of wolves into Yellowstone has been said to include a marked change in the ranging behaviour of deer which in turn has allowed significant changes in the vegetation. I wonder if something similar could happen in relation to mosquitoes. I know that herds of wild/feral equids in some parts of the world spend part of their day assembling in vegetation-free, dusty areas where they get some relief from biting flies. Without the flies they would be free to spend the whole time grazing in the areas they otherwise favour, potentially increasing the grazing pressure and the resultant impact on vegetation structure. In this case the biting flies are probably generally members of the tabanidae rather than mosquitoes but I could envisage mozzies having similar effects on behaviour of other host species in other habitats. I believe it is the case that biting flies and the diseases associated with them have prevented/hindered the penetration of humans and their livestock into some areas, prior to the availability of insecticide sprays, drugs etc. .

    1. Good point, Jonathan. I suspect populations of deer and other blood donors would shoot up. Without mosquitoes, they could feed, mate, and chew the cud (literally or not) in relative peace – deer flies and midges would keep bugging them, though.

  3. Thanks for the wonderful narration! Although I am familiar with thrips, and self-made elderberry jam is my favorite of all jams (but a lot of work), I had no idea of the connection between the two. An added bonus are Jonathan’s reflections on possible host/prey species behavior changes, should blood sucking insects disappear.

  4. I always lacked arguments to defend mosquitos (raison d’être) except maybe the food-for-other-animals-argument or the not well received fighting-global-warning-by-killing-people-argument. Hadn’t thought of pollination.

    Likewise, I always wondered about thunder bugs, I didn’t even know their name: “tripsen” (Dutch).

  5. IIRC, there is at least one study which looked at the consequences of the elimination of mosquitoes on the foodstream, and found them negligible.

  6. Thanks for the thrips info (I was part of the recent genome project on Frankinella, but did not know about some aspects of their biology). On the other hand, I am dismayed by your broad characterization of the current efforts to help control mosquito-vectored diseases. NONE of these attempt to eliminate all mosquitoes, indeed it is dismaying that a biologist would even think that feasible or imaginable, let alone acceptable. Instead, all efforts are highly targeted at individual species. For example, Aedes aegypti is an introduced species in the New World where it causes the most trouble transmitting a wide variety of viruses like dengue and Zika, causing major problems for both locals and tourists. Programs to control A. aegypti by genetic or other means (e.g. spreading Wolbachia bacterial infections that prevent their transmission of viruses, led by my ex-postdoc Scott O’Neill in Melbourne amoung others), are highly targeted at that one species with no risk of affecting or spreading to other species of the genus, let alone other genera like those found in Alaska. And I’d be willing to bet if you were a family in tropical or sub-tropical Africa that has lost a child to malaria you would applaud ongoing efforts to develop genetic means for the control of Anopheles gambiae and sibling species, complementing ongoing insecticide-impregnated bednet programs and possible vaccines.

    1. To be fair to Athayde I think his comments were more along the lines of a thought experiment about what the impact of complete eradication of mosquitoes might be (over and above the impacts in terms of disease control) rather than a clarion call to halt attempts at mosquito control or a suggestion that complete eradication is planned. Many people pose questions along the lines of ‘what is the point of mosquitoes/wasps/etc’ and it is of intellectual interest if nothing else to consider how these things interact with the rest of nature beyond just being pests* to us..

      I imagine when he says “Considering the magnitude of suffering, let alone the economic impact of mosquito-borne diseases, nobody could be blamed for wishing mosquitoes to disappear from the face of the Earth.” that can be taken to include your tropical African family that has lost a child to malaria.

      *I use the word ‘pest’ in the broadest sense to include anything that has a detrimental impact on us and not to trivialise the harmful impact of mosquitoes on human populations.

  7. Worth mentioning about thrips: they have asymmetrical mouthparts, with the right mandible reduced or even absent.

  8. Well, that’s weird. Part of 8, above, disappeared. Probably too late by now, but it should have read:

    This looks like a good place to ask this, that has been bugging me of late. Why is it poll EN yet poll IN ate/ation/ium ?

  9. Again, probably too late. But…

    1) Thank you for a fascinating post!

    2) I recently read “The Mosquito” by Timothy C. Winegard. While quite interesting, it was almost completely devoted to the effect of mosquito-borne diseases on human history, especially military history. I would like to read a more biologically and/or ecologically based book. Would you (or anyone else) have any good recommendations? Thanks in advance.

    1. I don’t know of any, Mark. You can find quite a bit of information scattered in the literature, but books, understandably, have focused on the medical entomology angle.

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