Tag Archives: Operophtera brumata

Not all moths have wings

Insects really took off when they developed flight (Alexander, 2015), so it is perhaps surprising that so many have lost the ability subsequently.  Nearly all the winged Orders have developed flightless members, with beetles of course, topping the list (Wagner & Liebherr, 1992).  A number of reasons for why flightlessness made a reappearance have been put forward. The eminent coloepterist, Thomas Vernon Wollaston, noted that the island of Madeira had an unusually high number of wingless (apterous) beetles. His friend, Charles Darwin, suggested that for island dwelling animals, it was a disadvantage to be winged especially if you were small or subjected to high winds (Darwin, 1859). Many years later, Derek Roff reviewed the literature, and found that there was no difference in the proportion of non-winged insects on islands compared with those on continental areas (Roff, 1990).  Winglessness is also common in insects living at high altitudes, in cold climates or in those that are autumn or winter active (Hackman, 1966).  It might be that wings are energetically costly in those environments (Mani, 1962), but why then is it that in many cases, it is only the females that are wingless?  To explain this we can hypothesise that eggs are energetically more expensive than sperm (Hayward & Gilooly, 2011), so that males can ‘afford’ to be winged and travel to find a mate. For this to work, the females need to be able to attract males from a distance, something moths are renowned for (Greenfield, 1981).

Male Thyridopteryx ephemeraeformis – note the well-developed antenna – ideal for picking up female sex pheromones. https://upload.wikimedia.org/wikipedia/commons/4/4d/-_0457_%E2%80%93_Thyridopteryx_ephemeraeformis_%E2%80%93_Evergreen_Bagworm_Moth_%2814869905567%29.jpg By Andy Reago & Chrissy McClarren [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)%5D, via Wikimedia Commons

We also know that in those insects with wing dimorphism, the apterous forms are more fecund compared with those with wings (Dixon, 1972; Mackay & Wellington, 1975). In those insects that retain their wings, many resorb their wing muscles once they have found suitable egg laying sites (Stjernholm et al., 2005; Tan et al., 2010), further proof that wings are costly. Winglessness is also common in those insects that are parasitic on vertebrates, bedbugs, fleas and lice for example.  Those that do start with wings, such as the Hippoboscid flies, lose their wings once they have found a suitable host. Finally, winglessness is often associated with stable and extensive habitats, such as forests, or surprisingly to me at any rate, mountains, where dispersal is not a high priority (Roff, 1990).

Thyridopteryx ephemaeraeformis https://ideastations.org/sites/default/files/storage/secondary-images/bagworm-case.jpg  

I first saw bagworms as a child in Jamaica but of course at the time had no idea what species they were. I was however, fascinated by the sight of the cunningly constructed cases in which the larvae lived and eventually pupated within.  To me, case bearer moths and caddisflies were the insect equivalent of hermit crabs, which were and are one of my favourite non-insect animals*.  Little did I know that one day I would write about these very same bagworms (Rhainds et al., 2008). Bagworms, of which just over half have wingless females, immediately contradict the cold climate hypothesis of winglessness, as many of them are tropical and there are just as many wingless species in the tropics as there are elsewhere (Rhainds et al., 2009). The bagworms belong to the family Pyschidae, which contain a 1000 species or so.  Not only do over half of these have wingless females, some also have females which are legless and never leave their pupal case, even mating in it.

Male Thyridopteryx ephemeraeformis bagworm mating with bag-enclosed female (Jones, 1927)

Even though the more primitive (less derived) members of the Psychidae have wings, the winged females are less active than the males (Rhainds et al. 2009).  As you might expect, host plant selection is by the larval stage, which on hatching, throw out a silk thread and float off with great expectations (Moore & Hanks, 2004).  Once they find a suitable host plant, which is not as difficult as you might expect, as they extremely polygamous, they begin to feed and construct their cases.  Some of the larval cases that Psychids construct are truly magnificent.  A great example is Eumeta crameri, the large faggot worm, so called because it looks like it is carrying a pile of firewood on its back 🙂

Eumeta crameri, the large faggot worm, so called because of the twigs its carries around on its back Melvyn Yeo

In case you are wondering about the ornate cases, they are not decorative, but more likely to be anti-predator devices (Khan, 2020).

Although the Psychids have the largest number of species with wingless females, there are 18 other moth families with species with wingless females.  Species that are found at high altitudes and northern latitudes have the most flightless species (Hackmann, 1966) or, like the Psychids, inhabit stable forest and woodland habitats (Barbosa et al., 1989).  Another characteristic of wingless moth species is that they overwinter as eggs or first instar larvae (Barbosa et al., 1989, although there are of course, many moths that have similar habits and are not wingless, such as the small ermine moths (Leather, 1986a).

After the Psychids, the families with the greatest number of species with wingless females are the Geometridae (loopers) and the Lymantridae (tussock moths). In the Lymantridae some are wingless and many have non-functional wings (Hackman, 1966).  The Arctidae and the Lasiocampidae also have some flightless species, the genus Chondrostega, endemic to the Iberian Peninsula having some notable examples, (Hackman, 1966). An oddity, as they are not strictly flightless, are females of the tortricid Choristoneura fumiferana, which have functional wings, but are behaviourally flightless, only taking flight under particular environmental conditions (Barbosa et al., 1989).

Moth species that have flightless females all have one thing in common, they aren’t picky about their diet, they are polyphagous and live in forests and woodlands. They also tend to have larvae that can disperse by ballooning, although not all moths with ballooning larvae have flightless females.  First instar larvae of the pine beauty moth, Panolis flammea, which readily balloon in outbreak situations, and usefully, can survive several days without food (Leather, 1986b).

In the UK there are two very common moths with wingless females, the winter moth, Operphthera brumata and the Vapourer moth, Orgyia antiqua, the former a Geoemtrid, the latter, a Lymantrid. Both are extremely polyphagous, usually feeding on broadleaf trees and shrubs, but both have recently added conifer species to their diets.  The Vapourer moth ‘decided’ that the introduced lodgepole pine, Pinus contorta growing in Sutherland and Caithness, would make a suitable alternative food plant (Leather, 1986) and the winter moth opted for another introduced conifer, Sitka spruce, Picea sitchensis, in the Scottish Borders (Hunter et al., 1991). Why both these host shifts happened in the early 1980s and in Scotland, remains a mystery, although it is possible that they moved onto conifers via heather (Hewson & Mardon, 1970; Kerslake et al., 1996).

They do, however, have some striking differences in their approach to life. Larvae of the Winter moth are spring flush feeders, and very dependent on egg hatch coinciding with bud burst (Wint, 1983), Vapourers are summer foliage feeders so are adapted to feeding on mature leaves. The adults of the Winter moth, as its name suggests are active in the winter months, laying their eggs on the bark or in crevices of their host trees in November and December and even January. Vapourer adults on the other hand are summer active, the eggs being laid on their pupal cases on the leaves of their host trees from July to September.

Female Vapourer moth and her egg mass – note the short legs and much reduced wings

 

Long legged female winter moth Operphtera brumata https://butterfly-conservation.org/sites/default/files/styles/large/public/2019-01/8179909985_76865dd047_o.jpg

Hackman (1966) distinguishes two types of wingless females, those with reduced locomotion, very heavy, filled with eggs and what I describe in class as splurgers, i.e. all their eggs laid in one go.  The female Vapourer with short legs and much-reduced wings is an ideal example.  The female winter moth is a good example of the second type, those possessing good strong legs which after copulation seek out suitable egg-laying sites.  Despite the difference in oviposition tactics, the first instar larvae of both species are adept ballooners, and it is they who ‘decide’ whether to stay or go (Tikkanen et al., 1999).

First instar Vapourer moth larvae in the process of dispersing.

Understandably, they have very little control of where they land, although presumably, they can reject the plant they land on and launch themselves into space again. How many times they can do this and how long they can live for without feeding, is something that needs research, but given that the first instar larvae of the pine specialist P. flammea can live several days without feeding, I would expect that the Winter moth and Vapourer moth larvae are equally capable of resisting starvation.

Moths without wings, but highly successful and many are pests, so not such a dumb approach to life after all?

And while we’re at it, here is the lymantriid Teia anartoides. With hamsterlike apterous females! AinsleyS @americanbeetles

References

Alexander, D.E. (2015) On the Wing, Oxford University Press. (This is an excellent book).

Barbosa, P., Krischik, V. & Lance, D. (1989) Life history traits of forest-inhabiting flightless lepidoptera. American Midland Naturalist, 122, 262-274.

Darwin, C. (1859) 0n the Origin of Species, JohnMurray, \lodnon.

Dixon, A.F.G. (1972) Fecundity of brachypterus and macropterous alatae in Drepanosiphum dixoni (Callaphididae, Aphididae). Entomologia experimentalis et applicata, 15, 335-340.

Greenfield, M.D. (1981) Moth sex pheromones: an evolutionary perspective. Florida Entomologist, 64, 4-17.

Hackman, W. (1966) On wing reduction and loss of wings in Lepidoptera. Notulae Entomologicae, 46, 1-16.

Hayward, A. & Gillooly, J.F. (2011) The cost of sex: quantifying energetic investment in gamete production by males and females. PLoS One, 6, e16557

Hewson, R. & Mardon, D.K. (1970) Damage to heather moorland by caterpillars of the vapourer moth Orgyia antiqua L. (Lep., Lymantridae). Entomologist’s Monthly Magazine, 106, 82-84.

Hunter, M.D., Watt, A.D. & Docherty, M. (1991) Outbreaks of the winter moth on Sitka spruce are not influenced by nutrient deficiencies of trees. Oecologia, 86, 62-69.

Jones, F.M. (1927) Mating of the Psychidae (Lepidoptera). Transactions of the Entomological Society of America, 53, 293-312.

Kerslake, J.E., Kruuk, L.E.B., Hartley, S.E. & Woodin, S.J. (1996) Winter moth (Operophtera brumata (Lepidoptera: Geometridae)) outbreaks on Scottish  moorlands; effects of host plant and parasitoids on larval survival and development. Bulletin of Entomological Research, 86, 155-164.

Khan, M.K. (2020) Bagworm decorations are an anti-predator structure.  Ecological Entomology https://onlinelibrary.wiley.com/doi/epdf/10.1111/een.12876

Leather, S.R. (1986a) Insects on bird cherry I The bird cherry ermine moth, Yponomeuta evonymellus (L.). Entomologist’s Gazette, 37, 209-213.

Leather, S.R. (1986b) The effect of neonatal starvation on the growth, development and survival of larvae of the pine beauty moth Panolis flammea. Oecologia, 71, 90-93.

Leather, S.R. (1986c) Keep an eye out for the vapourer moth. Forestry & British Timber, 15, 13.

Mackay, P.A. & Wellington, W.G. (1975) A comparison of the reproductive patterns of apterous and alate virginoparous Acyrthosiphon pisum (Homoptera: Aphididae). Canadian Entomologist, 107, 1161-166.

Mani, M.S. (1962) Introduction to High Altitude Entomology: Insect Life above the Timber-line in the Northwest Himalaya. Methuen, London.

Moore, R.G. & Hanks, L.M. (2004) Aerial dispersal and host plant selection by neonate Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae). Ecological Entomology, 29, 327-335.

Rhainds, M., Leather, S.R. & Sadoff, C. (2008) Polyphagy, flightlessness and reproductive output of females: a case study with bagworms (Lepidoptera: Psychidae). Ecological Entomology, 33, 663-672.

Rhains, M., Davis, D.R. & Price, P.W.(2009) Bionomics of Bagworms (Lepidoptera: Psychidae). Annual Review of Entomology, 54, 209-226.

Roff, D.A. (1990) The evolution of flightlessness in insects. Ecological Monographs, 60, 389-422.

Stjernholm, F., Karlsson, B. & Boggs, C.A. (2005) Age-related changes in thoracic mass: possible reallocation of resources to reproduction in butterflies. Biological Journal of the Linnean Society, 86, 363-380.

Tan, J.Y., Wainhouse, D.W., Day, K.R. & Morgan, G. (2010) Flight ability and reproductive development in newly-emerged pine weevil Hylobius abietis and the potential effects of climate change. Agricultural and Forest Entomology, 12, 427-434.

Tikkanen, O.P., Carr, T.G. & Roininen, H. (1999) Factors influencing the distribution of a generalist spring-feeding moth, Operophtera brumata (Lepidoptera: Geometridae), on host plants. Environmental Entomology, 28, 461-469.

Wagner, D.L. & Liebherr, J.K. (1992) Flightlessness in insects. Trends in Evolution & Ecology, 7, 216-219.

Watt, A.D., Evans, R. & Varley, T. (1992) The egg-laying behaviour of a native insect, the winter moth Operophtera brumata (L.) (Lep., Geometridae), on an introduced tree species, Sitka spruce, Picea sitchensis. Journal of Applied Entomology, 114, 1-4.

Wint, W. (1983) The role of alternative host-plant species in the life of a polyphagous moth, Operophtera brumata (Lepidoptera, Geomtridae). Journal of Animal Ecology, 52, 439-450.

Wollaston, T.V. (1854) Insecta Maderensia, John van Voorst, London.

 

 

 

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Insectageddon, Ecological Armageddon, Global insect Apocalypse – why we need sustained long-term funding

“To him that countryside, largely unspoiled in his early days, was an inexhaustible source of delight and a subject of endless study and mediation…And as the years passed and the countryside faded away under the withering touch of mechanical transport, that knowledge grew more and more precious. Now, the dwindling remnants had to be sought and found with considered judgement and their scanty material eked out with detail from the stores of the remembered past”  R Austin Freeman The Jacob Street Mystery (1942)

The recent release of the IPBES report highlighting the significant global declines in biodiversity has prompted me to revisit the “Insectageddon” debate, some of the ramifications of which I wrote about earlier this year.

 

Summary from the IPBES report – note that even a well-known group like dragonflies is quite data deficient*.

Insects may be in decline, but papers about their decline have been around for almost twenty years and even more are appearing as we entomologists begin to hope that people may at last be beginning to listen to us.

A selection of some of the many papers that have documented insect declines over the last several years.

Using the now infamous search term “insect decline” in the Google Trends function I was not surprised to see the steep increase since 2016, as 2017 was the year in which the paper reporting  the 75% decline in flying insect biomass appeared (Hallmann et al., 2017), but I was intrigued by what appeared to have been a peak in mentions since 2004.

Google Trends using the phrase insect decline – last data point is 2019 at the time of writing

I wondered what caused the peak in 2004, so using the same key words as Sánchez-Bayo & Wyckhuys (2019), checked Google Scholar and Web of Science to see if I could track down a paper that might have caused a media splash at the time.  I also checked 2003, in case there was a delay in reporting. To my surprise I couldn’t find anything relevant in 2004, but 2003 threw up three papers (Hopkins & Freckleton, 2002; Kotze & O’Hara, 2003; Dennis & Shreeve, 2003).  The first was about the decline of taxonomists, which although a serious problem is unlikely to have generated that much attention, the other two were about long-term declines in Carabid beetles (Kotze & O’Hara, 2003) and the third about the decline of French butterflies (Dennis & Shreeve, 2003) which again, I suspect were probably not high enough profile to generate a big splash.  I was puzzled but then I thought, why not just put it into Google with the date 2004, and sure enough it directed me to a Nature News item with the headline Insect deaths add to extinction fears, which in turn led me to Thomas et al., (2004) which I am pretty certain generated the peak in interest and also highlights the fact that ecologists and entomologists have been worrying about this problem for some time.

Since the appearance of the, now, infamous paper, that sparked the most recent round of Armageddon stories (Sánchez-Bayo & Wyckhuys, 2019), a lot has been, quite justifiably, written about the short-comings of the study both in scientific journals (e.g. Komonen et al., 2019, Simmons et al., 2019; Thomas et al, 2019, Wagner, 2019) and in blog posts, such as this thoughtful piece from Manu Saunders.

What does need to be stressed, is that although these commentators recognise the shortcomings of the paper, none of them, including the most scathing of commentators (Mupepele et al., 2019) dispute the fact, that insects, in general, are in decline. Unfortunately, the climate change deniers and their ilk, have, of course, used the criticisms to try and spread a message of “nothing to fear folks”.

Hopefully a failed attempt at downplaying the insect decline stories, but a great example of how climate change deniers are keen to muddy the waters

For humans with our relatively short lifespans, shifting baselines can be a problem (Leather & Quicke, 2010; Tree, 2018), in that people accept what they have known in their childhoods as the natural state of nature.  It can of course work the other way. I can remember the late great Miriam Rothschild telling me in the early 1990s, how as a “gel” in the 1920s a particular butterfly species that was currently at very low numbers compared with the 1970s which was what I and similar aged colleagues were remarking upon, was 50 years before that, also very low, her message being “populations cycle”.  It is because of this propensity, which is nicely illustrated by some of my 20-year data sets, all from the same 52 trees, that we need access to long-term funding to monitor insect populations.  Chop my data sets into three-year concurrent periods, the time-span of a typical PhD study or research grant, and you end up with some very different pictures of the populations of three common insect species.

The Silwood Park Winter moth, Operophtera brumata – dramatic shifts in population levels

Twenty years of the Sycamore aphid, Drepanosiphum platanoidis, at Silwood Park.  First five years versus last five years – what happened? Does this fit with the recent paper by Stephen Heard and colleagues that species chosen for study because they are common or easy to find, are almost certainly to show declines over the long-term?

 

The Maple aphid, Periphyllus testudinaceus – twenty-year data run from Silwood Park

Given the above, and the fact that most of the evidence for insect declines is largely based on studies from Europe, the UK heading the list (Wagner, 2019) and on top of that, the evidence from tropical locations is open to different interpretations (e.g.  Willig et al, 2019), there is an urgent need for something to be done.  So, what do we need to do?  I think there are three things that need addressing, sooner, rather than later.

Monitoring

First, we need to build on the work that has been done in Germany (Hallmann et al., 2017) and the UK via the Rothamsted Insect Survey (Bell et al., 2015) and establish active insect monitoring networks using repeatable sampling methods, but on a global scale. New monitoring programs will not help establish past baselines, but they can help us determine trends from this point forward. We can make this truly global by engaging the public through community science. These programs will need to use standardized methods, such as Malaise traps, pitfall traps, light traps, and effort-based counts, with species diversity, abundance and biomass being primary measures. Although biomass is an imperfect estimator because it can be sensitive to changes in abundances of large species, it is still a valuable metric from the ecosystem perspective. Determining biomass trends also does not require fine-scale taxonomic knowledge, which is often lacking in citizen science initiatives. It would, even if it were possible, be incredibly expensive, to try to monitor all insect species from any community with appreciable diversity.  A much better option, and one that will certainly appeal to a wide range of citizen scientists would be to monitor taxa like butterflies, macro-moths, dragonflies, bees, and some beetle groups.  All these can serve as indicator species for other insect groups and, tongue in cheek, many can be observed using binoculars, thus encouraging ornithologists and mammalologists to join in 😊

Innovative use of past data

At national levels, a few long-term monitoring schemes already exist, for example, the UK Environmental Change Network (http://www.ecn.ac.uk/ ) collects biotic and abiotic data, including many insect groups, from 57 different sites across the UK using identical protocols (Rennie, 2016).   Multiple Long-Term Ecological Research projects track different facets of ecosystems in different ways (Magurran et al., 2010). In fact, the LTER network, if expanded to a global scale, could be the natural framework to make a global network proposal feasible, possibly through a targeted step change in funding (Thomas et al., 2019).  This is great for the future, but unfortunately, all the active long-term monitoring schemes are younger than modern agricultural intensification.  A way forward would be to use museum collections and to construct data sets by going through back numbers of those entomological journals that pre-date the 1940s.  There are some long-term historical long-term data that are already accessible, for example the 150 year record pine beauty moth infestations in Germany dating from 1810 (Klimetzek, 1972) and I am sure that others must exist.

Funding

Whatever we do, it will need long-term funding. There needs to be a recognition by state research funding agencies that entomological survey and monitoring work, although appearing mundane, should receive a step-change in funding, even if it is at the expense of other taxa  Funding should reflect the diversity and abundance of taxa, not their perceived charisma (Clark & May, 2002; Leather, 2013).  Crowd-funding may draw in some funding, but what is required is stable, substantial and sustained funding that will allow existing and future international collaborations to flourish.  For this to happen and failing sustained state funding, we need to convince philanthropic donors such as the Gates Foundation to turn their attention from insect eradication to insect conservation.

We do, however, need to act quickly, stop talking to just our peers, meet the public, and, if needs be, personally, or via our learned societies, lobby governments; there is no Planet B.

 

References

Bell, J.R., Alderson, L., Izera, D., Kruger, T., Parker, S., Pickup, J., Shortal, C.R., Taylor, M.S., Verier, P., & Harrington, R. (2015) Long-term phenological trends, species accumulation rates, aphid traits and climate: five decades of change in migrating aphids. Journal of Animal Ecology, 84, 21-34.

Cordoso, P. & Leather, S.R. (2019) Predicting a global insect apocalypseInsect Conservation & Diversity, 12, 263-267.

Dennis, R.H.L. & Shreeve, T.G. (2003) Gains and losses of French butterflies: tests of predictions, under-recording and regional extinction from data in a new atlas. Biological Conservation, 110, 131-139.

Hallmann, C.A., Sorg, M., Jongejans, E., Siepel, H., Hoflan, N., Schwan, H., Stenmans, W., Muller, A., Sumser, H., Horren, T., Goulson, D., & De Kroon, H. (2017) More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoSONE, 12(10), :e0185809.

Hopkins, G.W. & Freckleton, R.P. (2002) Declines in the numbers of amateur and professional taxonomists: implications for conservation. Animal Conservation, 5, 245-249.

Klimetzek, D. (1972) Die Zeitfolge von Ubervermehrungen nadelfressender kiefernraupen in derPfalz seit 1810 und die Ursachen ihres Ruckanges in neuerer Zeit. Zeitschrift fur Angewandte Entomologie, 71, 414-428.

Kotze, D.J. & O’Hara, R.B. (2003) Species decline – but why?  Explanations of Carabid beetle (Coleoptera, Carabidae) declines in Europe. Oecologia, 135, 138-148.

Leather, S.R. & Quicke, D.J.L. (2010) Do shifting baselines in natural history knowledge threaten the environment?  Environmentalist, 30, 1-2

Magurran, A.E., Baillie, S.R., Buckland, S.T., Dick, J.M., Elston, D.A., Scott, M., Smith, R.I., Somerfiled, P.J. & Watt, A.D. (2010) Long-term datasets in biodiversity research and monitoring: assessing change in ecological communities through time. Trends in Ecology and Evolution, 25, 574-582.

Møller, A.P. (2019) Parallel declines in abundance of insects and insectivorous birds in Denmark over 22 years. Ecology & Evolution, 9, 6581-6587.

Mupepele, A.C., Bruelheide, H., Dauber, J., Krüß, A., Potthast, T., Wägele, W. & Klein, A.M. (2019). Insect decline and its drivers: Unsupported conclusions in a poorly performed meta-analysis on trends—A critique of Sánchez-Bayo and Wyckhuys (2019).  Basic & Applied Ecology, 37, 20-23.

Rennie, S.C. (2016) Providing information on environmental change: Data management, discovery and access in the UK Environmental Change Network data.  Ecological Indicators, 68, 13-20.

Sánchez-Bayo, F. & Wyckhuys, K.A.G. (2019) Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232, 8-27.

Thomas, C.D., Jones, T.H. & Hartley, S.E. (2019) “Insectageddon”: a call for more robust data and rigorous analyses. Global Change Biology, 6, 1891-1892.

Thomas, J.A., Telfer, M.G., Roy, D.B., Preston, C.D., Greenwood, J.J.D., Asher, J., Fox, R., Clarke, R.T. & Lawton, J.H. (2004) Comparative losses of British butterflies, birds, and plants and the global extinction crisis. Science, 303, 1879-1881.

Tree, I. (2018) Wilding, Picador, Pan Macmillan.

Wagner, D.L. (2019) Global insect decline: comments on Sánchez-Bayo and Wyckhuys (2019). Biological Conservation, 233, 332-333.

Willig, M.R., Woolbright, L., Presley, S.J., Schowalter, T.D., Waide, R.B., Heartsill Scalley, T., Zimmerman, J.K.,  González, G. & Lugo, A.E. (2019) Populations are not declining and food webs are not collapsing at the Luquillo Experimental Forest. Proceedings of the National Academy of Sciences, 116, 12143-12144.

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