Category Archives: Conservation

Friday Fellow: Emerald Ash Borer

by Piter Kehoma Boll

It’s time for our next beetle and this time our fellow is a species that spent its first century after discovery without calling much attention but then something happened. Its name is Agrilus planipennis and is commonly known as the emerald ash borer.

An adult emerald ash borer in Virginia, USA. Photo by Bryan Wright.*

Native from East Asia, the emerald ash borer is found in southeastern Russia, Mongolia, northern China, Korea and Japan. Adults measure about 8.5 mm in length and have a metalic green color on the head, pronotum and elythra, and an iridescent-purple metalic color on the dorsal side of the abdomen, seen when the wings are open. They live in the canopy of ash trees (Fraxinus spp.) during spring and summer and feed on their leaves.

After about a week as adults, the emerald ash borers start to mate. Females remain on the trees and males hover around looking for them. Once a female is located, the male drops over her and they start to mate. After mating is concluded, females live for some more weeks and typically lay about 40 to 70 eggs, although some live longer and may lay up to 200 eggs.

Dorsal view of an emerald ash borer with open wings showing the iridescent-purple abdomen.

The eggs are laid between crevices or cracks of the bark and hatch about two weeks later. The newly hatched larvae chew through the bark, reach the inner tissues of the trunk and start to feed on them. They reach up to 32 mm in length in the fourth instar, more than three times the length of the adult, and pupate during spring, emerging as adults soon after. In China, adults emerge from the trees in May.

A larva inside an ash tree in Pennsylvania, USA. Credits to the Pennsylvania Department of Conservation and Natural Resource.**

In its native area, the emerald ash borer can be a nuisance but is not highly problematic to ash trees because it occurs in low densities. However, in 2002, the species was found in the United States feeding on local ash species. Since the emerald ash borer has no natural predators in North America and the ash species in this continent did not evolve to be resistant to infection, it started to spread very quickly. In less than two decades, the beetle has killed millions of ash trees and is a serious threat to the more than eight billion ash trees found in North America. With the death of ash trees, North American forests become vulnerable to more invasive species, which will only worsen the scenario.

Damage caused by the larvae to a tree in New York state, USA. Photo by iNaturalist user bkmertz.*

In order to control the spread of the emerald ash borer, ash trees are treated with pesticides. Four parasitoid wasps from China known to attack only the emerald ash borer have also been released in North America to help control the spread and their success is still being assessed. Traps, such as glue-covered purple panels, which are visually attractive to the beetles, are also used to capture the animals and determine the extent of the invasion.

Once more, a completely fine species has led to an ecological disaster due to human influence and now we are running to find ways to avoid an ecosystem collapse throughout an entire continent.

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References:

Francese JA, Mastro VC, Oliver JB, Lance DR, Youssef N, Lavallee SG (2005) Evaluation of colors for trapping Agrilus planipennis (Coleoptera: Buprestidae). Journal of Entomological Science 40(1): 93-95.

Liu H, Bauer LS, Miller DL, Zhao T, Gao R, Song L, Luan Q, Jin R, Gao C (2007) Seasonal abundance of Agrilus planipennis (Coleoptera: Buprestidae) and its natural enemies Oobius agrili (Hymenoptera: Encyrtidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae) in China. Biological Control 42(1): 61-71. doi: 10.1016/j.biocontrol.2007.03.011

Wang XY, Yang ZQ, Gould JR, Zhang YN, Liu GJ, Liu ES (2010) The biology and ecology of the emerald ash borer, Agrilus planipennis, in China. Journal of Insect Science 10(1): 128. doi: 10.1673/031.010.12801

Wikipedia. Emerald ash borer. Available at < https://en.wikipedia.org/wiki/Emerald_ash_borer >. Access on 9 December 2019.

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**Creative Commons License This work is licensed under a Creative Commons Attribution 3.0 Unported License.

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Filed under Conservation, Entomology, Extinction, Friday Fellow

Should we save or should we get rid of parasites?

by Piter Kehoma Boll

Parasites are special types of organisms that live on or inside other lifeforms, slowly feeding on them but usually not killing them, just reducing their fitness to some degree. This is a much more discrete way to survive than killing or biting entire parts off, as predators (both carnivores and herbivores) do. However, different from these creatures, parasites are often regarded as unpleasant and disgusting. Yet parasitism is the most common way to get food in nature.

When I introduced the rhinoceros tick in a recent Friday Fellow, I mentioned the dilemma caused by it. Since the rhinoceros tick is a parasite of rhinoceroses, and rhinoceroses are threatened with extinction, a common practice to improve the reproductive fitness of rhinos is removing their ticks, but this may end up leading the rhinoceros tick to extinction.

This actually happened already with other parasites, such as the louse Coleocephalum californici, which was an exclusive parasite of the California condor Gymnogyps californianus. In order to save the condor, a common practice among veterinarians working with conservationists was to delouse the birds and, as a result, this louse is now extinct. The harm that the louse caused to the condor was so little, though, that its extinction was not at all necessary, being nothing more than a case of negligence and lack of empathy for a small and non-charismatic species.

The California condor louse Coleocephalum californici was extinct during a poorly managed campaign to save the California condor Gymnogyps californianus. Image extracted from https://www.hcn.org/blogs/goat/the-power-and-plight-of-the-parasite

The louse Rallicola (Aptericola) pilgrimi has also vanished forever during the conservation campaigns to save its host, the little spotted kiwi, Apteryx owenii, in another failed work.

The efforts to save the little spotted kiwi, Apteryx owenii, from extinction led to the extinction of its louse. Photo by Judi Lapsley Miller.*
The now extinct Rallicola (Aptericola) pilgrimi. Credits to the Museum of New Zealand.***

Another group of parasites that is facing extinction are fleas. The species Xenopsylla nesiotes was endemic to the Christmas Island together with its host, the Christmas Island rat, Rattus macleari. The introduction of the black rat, Rattus rattus, in the island led to a quick decline in the population of the Christmas Island rat, which went extinct at the beginning of the 20th century and, of course, the flea went extinct with it. The flea Acanthopsylla saphes has likely become extinct as well. It was a parasite of the eastern quoll, Dasyurus viverrinus, in mainland Australia. The eastern quoll today is only found in Tasmania, as the mainland Australia’s population went extinct in the mid-20th century. However, the flea was never found in the Tasmanian populations, so it is likely that it died away in mainland Australia together with the local population of its host.

The Manx shearwater flea Ceratophyllus (Emmareus) fionnus. Photo by Olha Schedrina, Natural History Museum.*

But things have been changing lately and fortunately the view on parasites is improving. A recent assessment was made on the population of another flea, the Manx shearwater flea, Ceratophyllus (Emmareus) fionnus. This flea is host-specific, being found only on the Manx shearwater Puffinus puffinus. Although the Manx shearwater is not at all a threatened species and has many colonies along the North Atlantic coast, the flea is endemic to the Isle of Rùm, a small island off the west coast of Scotland. Due to the small population of its host in this island, the flea has ben evaluated as vulnerable. If the Manx shearwater population in the Island were stable, things would be fine but, as you may have guessed already, things are not fine. Just like it happened in Christmas Island, the black rat was also introduced in the Isle of Rúm and has become a predator of the Manx shearwater, attacking its nests.

The Manx shearwater, Puffinus puffinus, is the sole host of the Manx shearwater flea. Photo by Martin Reith.**

Some ideas have been suggested to protect the flea from extinction. One of them is to eradicate the black rat from the Isle or at least manage its population near the Manx shearwater colonies. Another proposal is to translocate some fleas to another island to create additional populations in other Manx shearwater colonies.

But why bother protecting parasites? Well, there are plenty of reasons. First, they comprise a huge part of the planet’s biodiversity and their loss would have a strong impact on any ecosystem. Second, they are an essential part of their host’s evolutionary history and are, therefore, promoters of diversity by natural selection. Removing the parasites from a host would eventually decrease its genetic variability and let it more vulnerable to other new parasites. Due to their coevolution with the host, parasites are also a valuable source of knowledge about the host’s ecology and evolutionary history, helping us know their population dynamics. We can even find ways to deal with our own parasites by studying the parasites of other species, and parasites are certainly something that humans managed to collect in large numbers while spreading across the globe.

Parasites may be annoying but they are necessary. They may seem to weaken their host at first but, in the long run, what doesn’t kill you makes you stronger.

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References:

Kirst ML (2012) The power and plight of the parasite. High Country News. Available at < https://www.hcn.org/blogs/goat/the-power-and-plight-of-the-parasite >. Access on 3 November 2019.

Kwak ML (2018) Australia’s vanishing fleas (Insecta: Siphonaptera): a case study in methods for the assessment and conservation of threatened flea species. Journal of Insect Conservation 22(3–4): 545–550. doi: 10.1007/s10841-018-0083-7

Kwak ML, Heath ACG, Palma RL (2019) Saving the Manx Shearwater Flea Ceratophyllus (Emmareus) fionnus (Insecta: Siphonaptera): The Road to Developing a Recovery Plan for a Threatened Ectoparasite. Acta Parasitologica. doi: 10.2478/s11686-019-00119-8

Rózsa L, Vas Z (2015) Co-extinct and critically co-endangered species of parasitic lice, and conservation-induced extinction: should lice be reintroduced to their hosts? Oryx 49(1): 107–110. doi: 10.1017/S0030605313000628

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*Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 International License.

**Creative Commons License This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

***Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License.

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Filed under Conservation, Ecology, Evolution, Extinction, Parasites

Daytrippers’ chips are killing species in protected areas

by Piter Kehoma Boll

Leia em português

There’s nothing as threatening to nature as humans, as we all know. A lot of species have become endangered and even extinct due to human influence all around the world. As an attempt to protect whatever is left, we have been creating protected areas where species should be able to live their lives without the dangers of humanity.

However, in order to raise awareness about the importance of preserving the biodiversity, most protected areas accept human visitors. Although it does have some effect to improve the visitors’ view about nature and its importance, there are a lot of undesired side effects. Humans walking through a forest cause noise that disturbs the local fauna and the soil compaction caused by walking can lead to changes in vegetation growth and soil drainage.

But another human behavior that appears to have serious consequences on biodiversity conservation is our tendency to carry food with us, such as snacks, and eat it anywhere. People visiting a protected area may eat something on the way through the woods or stop for a picnic. Many species love food remains left by humans and will thrive with them.

Two Steller’s jays in Big Basin Redwoods State Park. Photo by iNaturalist user kgerner.*

One species that benefits from human food is the Steller’s jay, Cyanocitta stelleri, a corvid that is common across the the west coast of North America. As a result, this species is not at all threatened at the moment and it tends even to follow humans because of the easy access to food. In the wild, this species is a generalist omnivore, feeding on seeds, fruits, invertebrates, eggs and small vertebrates, such as rodents and bird nestlings.

Another bird that can be found in the same areas as the Steller’s jay is the marbled murrelet Brachyramphus marmoratus, a small seabird. Different from most seabirds, the marbled murrelet does not nest in cliffs or burrows near the water but on branches of old-growth conifers. As a result, they may move up to 80 km inland to find a suitable place to nest. Different from the Steller’s jay, the marbled murrelet does not benefit from human snacks. On the contrary, they may be its ruin.

A young marbled murrelet found in the Big Basin Redwoods State Park. Photo by iNaturalist user basinbird.*

The marbled murrelet relies heavily on old forests to reproduce and the female lays only one egg per year, leading to a low reproductive rate. Due to the removal of old forests by humans, the marbled murrelet has lost a lot of its original habitat and is currently considered an endangered species.

One of the few remaining areas for this species to nest is located in the Big Basin Redwoods State Park in California. The park contains many options for camping, which means humans bringing food all the time. This attracts a lot of Steller’s jays, which feast on the crumbs and other remains, and reproduce explosively. When humans are not present, this increased population migrates toward new areas, sometimes following humans to the cities, or starts to feed on whatever is present in the park, and one of the most nutritious options are nestlings of the marbled murrelet.

With an already endagered population, the marbled murrelet is about to get extinct because our desire to walk through the woods is accidentally increasing the population of one of its main predators. Will we ever be able to have a good impact on this planet?

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Hundreds of lionfish were released in the Atlantic out of pity

Antidepressants in wastewater are unbalancing foood webs

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Reference:

West EH, Brunk K, Peery MZ (2019) When protected areas produce source populations of overabundant species. Biological Conservation 238: 108220. doi: 10.1016/j.biocon.2019.108220

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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Filed under Conservation, Extinction, Ornithology

Friday Fellow: Rhinoceros Tick

by Piter Kehoma Boll

Parasites exist everywhere and, although most of us see them as hateful creatures, more than half of all known lifeforms live as a parasite at least in part of their life. And there are likely many more yet unknown parasites around there. Today I’m going to talk about one of them, which is found in large portions of Africa.

Its name is Dermacentor rhinocerinus, known as the rhinoceros tick. As its name suggests, it is a tick, therefore a parasitic mite, and its adult stage lives on the skin of the white rhinoceros (Ceratotherium simum) and the critically endangered black rhinoceros (Diceros bicornis).

A male rhinoceros tick attached to the skin of a rhinoceros in South Africa. Credits to iNaturalist user bgwright.**

Male and female rhinoceros ticks are considerably different. In males, the body has a black background with many large orange spots. In females, on the other hand, the abdomen is mainly black with only two round orange spots and the plate on the thorax is orange with two small dark spots. Males and females mate on the surface of rhinoceroses. After mating, the female starts to increase in size while the eggs develop inside her and then drops to the ground, laying the eggs there.

A female rhinoceros tick patiently waiting for a rhinoceros to come close. Photo by Martin Weigand.**

The larvae, as soon as they hatch, start to look for another host, usually a small mammal such as rodents and elephant shrews. They feed on this smaller host until they reach the adult stage, when they drop to the ground and climb on the surrounding vegetation, waiting for a rhinoceros to pass by and then attaching to them.

Conservation efforts to preserve biodiversity are mainly focused on vertebrates, especially mammals and birds. Rhinoceroses, which are an essential host for the rhinoceros tick to survive, are often part of conservation programs and, in order to increase their reproductive success, the practice of removing parasites from their skin is common. This is, however, bad for the rhinoceros ticks. If their host is endangered, they are certainly endangered too, and removing them worsens their condition. Are parasites less important for the planet? Don’t they deserve to live just as any other lifeform? We cannot forget that nature needs more than only what we consider cute.

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More mites and ticks:

Friday Fellow: Giant Red Velvet Mite (on 22 June 2016)

Friday Fellow: Cuban-Laurel-Thrips Mite (on 28 June 2019)

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References:

Horak IG, Fourie LJ, Braack LEO (2005) Small mammals as hosts of immature ixodid ticks. Onderstepoort Journal of Veterinary Research 72:255–261.

Horak IG, Cohen M (2001) Hosts of the immature stages of the rhinoceros tick, Dermacentor rhinocerinus (Acari, Ixodidae). Onderstepoort Journal of Veterinary Research 68:75–77.

Keirans JE (1993) Dermacentor rhinocerinus (Denny 1843) (Acari: Ixodida: Ixodidae): redescription of the male, female and nymph and first description of the larva. Onderstepoort Journal of Veterinary Research 60:59–68.

Mihalca AD, Gherman CM, Cozma V (2011) Coendangered hard ticks: threatened or threatening? Parasites & Vectors 4:71. doi: 10.1186/1756-3305-4-71

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**Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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Filed under Arachnids, Conservation, Friday Fellow, Parasites, Zoology

Alien invasions: the resistance lies in streams

by Piter Kehoma Boll

Human activities have been introducing, either deliberately or accidentally, several species in areas outside of their native range. Many os these species, when they reach a new ecosystem, can have devastating effects on the local communities.

One common practice is the introduction of exotic fish for food production or recreation. Although the impact of exotic fish species can be severe, there are several factors that modulate this severity. However, one situation in which it can have catastrophic outcomes is when fish are introduced in water bodies that were originally fishless.

Mountain streams and lakes are usually fishless because of physical barriers, especially waterfalls, as they prevent fish from moving upstream. But fish have been introduced in many mountain lakes to provide a local food stock or for sport fishing.

One place that was plagued this way is the Gran Paradiso National Park in the Western Italian Alps. During the 1960s, the brook trout, Salvelinus fontinalis, a fish that is native from North America, was introduced in several of the park’s high-altitude lake. Later, when the area became proteced, fishing was prohibited.

Salvelinus fontinalis, the brook trout. Photo by Alex Wild.

From 2013 to 2017, a fish erradication program was conducted in four lakes of the park, namely Djouan, Dres, Leynir and Nero. Fish were captured using gillnetting and electrofishing. Since the trouts had colonized the streams that are connected to the lakes, they had to be removed from there as well.

The communities of organisms living in the lakes and streams were monitored to assess their recovery after the fish removal. The lakes showed a remarkable resilience, reaching a community structure similar to that of lakes where fish were never introduced. The streams, on the other hand, did not show a great difference before and after fish removal. The reason, however, was not that streams have low resilience. On the contrary, streams showed a great resistance to fish invasion. Trouts did not seem to have affected the macroinvertebrate communities of streams that much. But why is it so?

Dres lake in the Gran Paradiso National Park. Image extracted from the park’s website (http://www.pngp.it).

One hypothesis was that macroinvertebrates constantly colonize the streams by passive dispersion, coming from upstream waters. However, this is not applicable to streams that drain the lakes, as lake and stream communities are very different. Lower predation by trouts is not an option either, because it was shown that stream trouts actually eat more than lake trouts. Maybe stream invertebrates reproduce more quickly than lake ones? No! Studies have shown than this is similar in both environments.

The reason why stream invertebrates are less affected by the introduction of fish is still a mystery. One possible explanation is that streams present more microhabitats that are not explored by the trouts, providing refuges for the invertebrates. We need more studies to understand what is going on.

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You may also like:

Exotic species: are they always a trouble?

The New Guinea Flatworm visits France – a menace

Obama invades Europe: “Yes, we can!”

Think of the worms, not only of the whales, or: how a planarian saved an ecosystem

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References:

Tiberti R, Bogliani G, Brighenti S, Iacobuzio R, Liautaud K, Rolla M, Hardenberg A, Bassano B. (2019) Recovery of high mountain Alpine lakes after the eradication of introduced brook trout Salvelinus fontinalis using non-chemical methods. Biological Invasions 21: 875–894. doi: 10.1007/s10530-018-1867-0

Tiberti R, Brighenti S (2019) Do alpine macroinvertebrates recover differently in lakes and rivers after alien fish eradication? Knowledge & Management of Aquatic Ecosystems 420: 37. doi: 10.1051/kmae/2019029

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Filed under Conservation, Ecology, Fish

Friday Fellow: Portuguese Millipede

by Piter Kehoma Boll

Millipedes, which make up the class Diplopoda, are very cute arthropods in my opinion and include amazing species, such as the animal with the largest number of legs in the world. Many species are not well studied, though. However, one that is very well known is the Portuguese Millipede Ommatoiulus moreleti.

As its common name suggests, the Portuguese millipede is native from Portugal, more precisely from Southern Portugal and nearby areas in Spain, living in the soil of pine and oak forests. Its body, measuring about 4 cm as adults, has the typical cylindrical and elongate shape seen in most millipedes and is very dark, almost black, with legs that have a light color, usually whitish, but sometimes purplish.

A Portuguese millipede in Portugal. Photo by Romulo Arrais.*

Despite its relatively small size, the Portuguese millipede takes more than a year to reach maturity and grow for about three years. The mating period is usually during Autumn, and after having its eggs fertilized, the female lays from 60 to 80 of them in a chamber about 2 cm deep in the soil. When the eggs hatch, the first stage is a small, pupoid legless animal that remains inside a membrane until it molts into a small six-legged larva. During the first year, the juvenile molts about 8 times and the number of legs increases at each new stage. At about stage 10, they are sexually mature, but continue to molt and gaining more legs until reaching about 90 legs at the 14th stage. Males have an interesting reproductive strategy called periodomorphism, in which mature individuals molt into a “castrated” form, with reduced sexual organs, and becomes sexually mature again in the next molt, only to return to the immature form again in the next molt and so on.

The Portuguese millipede became famous after its accidental introduction in southeastern Australia, apparently in the 1950s. It soon became a very abundant species and, as a consequence, a nuisance for humans. As most millipedes, the Portuguese millipede is mainly detritivorous, feeding on dead plant material, such as rotten wood and dead leaves, so its introduction is not that much an ecological catastrophe, although it can have some negative impacts by competing with native millipede species.

A Portuguese millipede in Australia. Photo by iNaturalist user corunastylis.**

The main problems caused by the introduction of the Portuguese millipede in Australia affect mostly humans. They are attracted to weak light sources, such as those emitted by houses at night, and, as a result, end up invading residences, sometimes hundreds of them at a time. When threatened, the Portuguese millipede emits a pungent yellow secretion that can irritate the eyes and, in contact with clothes, mark them with a permanent stain. Addtionally, the Portuguese millipede sometimes can feed on some crops, especially fruits.

In Portugal, the populations of the Portuguese millipede are controlled by native predators, such as the European hedgehog Erinaceus europaeus and the beetle Ocypus olens. Released from these natural enemies, the millipede spread quickly through southeastern Australia. However, about 30 years later, its population in Australia started to decrease. Apparently some nematode parasites that infect native millipedes adapted to parasitize this invasive species as well, helping to contain its population size. Some other native Australian predators have also observed feeding on the Portuguese millipede, including the blue garden flatworm, Caenoplana coerulea.

Other than Australia, the Portuguese millipede was also introduced in several Atlantic Islands, such as the Macaronesian Islands, Bermuda and the UK, as well as in South Africa. However, it does not seem to be that much of a nuisance there.

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More millipedes:

Friday Fellow: Leggiest Millipede (on 12 February 2016)

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References:

Baker GH (1985) Predators of Ommatoiulus moreletii (Lucas) (Diplopoda: Iulidae) in Portugal and Australia. Australian Journal of Entomology 24(4): 247–252. doi: 10.1111/j.1440-6055.1985.tb00237.x

Baker GH (1978) The post-embryonic development and life history of the millipede, Ommatoiulus moreletii (Diplopoda: Iulidae), introduced in south-eastern Australia. Journal of Zoology 186: 209–228. doi: 10.1111/j.1469-7998.1978.tb03366.x

Gregory SJ, Owen C, Jones G, Williams E (2018) Ommatoiulus moreleti (Lucas) and Cylindroiulus pyrenaicus (Brölemann) new to the UK (Diplopoda, Julida: Julidae) and a new host for Rickia laboulbenioides (Laboulsbeniales). Bulletin of the British Myriapod & Isopod Group 30: 48–60.

McKillup SC, Allen PG, Skewes MA (1988) The natural decline of an introduced species following its initial increase in abundance: an explanation for Ommatoiulus moreletii in Australia. Oecologia 77:339–342. doi: 10.1007/BF00378039

Terrace TE, Baker GH (1994) The blue land planarian, Caenoplana coerulea Moseley (Tricladida: Geoplanidae), a predator of Ommatoiulus moreleti (Lucas) (Diplopoda: Julidae) in southern Australia. Australian Journal of Entomology 33(4): 371–372.

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License.

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Instead of toxic chemicals, use helping plants to get rid of crop pests

by Piter Kehoma Boll

Finding efficient ways to deal with agricultural pests in crops is a challenging work. Currently, as we all known, the main strategy to control such pests is the use of chemical pesticides. However, this approach only serves the interests of those seeking profit over well-being, as we all know that such pesticides increase the risk of several health issues in those consuming the crops. More than that, chemical pesticides not only kill the targeted pest but many other life forms, causing a devastating effect on ecosystems.

The cross-striped cabbageworm (Evergesis rimosalis) is a common pest in plants of the genus Brassica (kale, cabbage, mustard) in the eastern United States. Photo by iNaturalist user margaridamaria.*

Fortunately, there has been an increasing interest in finding alternative, healthier ways to deal with the problem. One way is the production of genetically modified organisms (GMOs) that are naturally resistant to pests. There are, however, two main problems with this approach. The first one is that the population in general has an irrational fear of GMOs, apparently believing that they can be more harmful than the poisonous chemical pesticides, which is completely absurd. The second problem with GMOs is that the technology to create them is dominated by the same companies that produce most pesticides and, as all big companies, only seek profit and do not give a damn about the people and the environment.

A third strategy is the use of natural enemies of the pests to control them in organic farms. Although many natural enemies are great doing their job, they may also cause negative impacts by interfering with the surrounding ecosystems. Many crop pests are not native from the area where they are pests, i.e., they are invasive species and, in order to control them efficiently, a predator from its native area must be introduced as well, and this predator may end up becoming a threat to other species that it elects as food.

Coleomegilla maculata is a common predatory lady beetle in the eastern United States. They are great to control agricultural pests locally but should not be deliberately introduced elsewhere. Photo by Riley Walsh.*

Fortunately, some nice strategies have been recently developed. One of them includes the use of additional plants in the fields that change the way that pests behave without posing a threat to surrounding areas. These additional plants consists of two types: trap crops and insectary plants.

The common buckwheat Fagopyrum esculentum has been used as an insectary plant. Photo by iNaturalist user jimkarlstrom.*

A trap crop, as the name suggests, is an additional crop that is not intended to be commercially exploited, but serves as a trap for the pests. Instead of attacking the main crop (called the ‘cash crop’), the pests are attracted to the trap crop, reducing their density in the cash crop. This system is more efficient if the trap crop is similar to the cash crop, such as another plant of the same genus, or another variety of the same species, because it must be as attractive to the pest as the cash crop, or perhaps even more attractive.

Insectary plants, on the other hand, are intended to attract other insects to the plantation, especially predatory insects that prey on the agricultural pest. Insectary plants should produce flowers in abundance, thus attracting many insect species, which will increase the interest of predators in the area. However, when used alone, insectary plants will only provide predators to control the pest in crop plants that are near the insectary plants and, as they are usually planted in an area surrounding the plantation, they would not protect the plants that are near the center of the plantation.

In a recent study, Shrestha et al. (see references) decided to combine trap crops and insectary plants together with the cash crops in a strategy that they called a ‘botanical triad’. The cash crap was organic cabbage (Brassica oleracea var. capitata) planted in the eastern United States; the trap crops were three other crops of the genus Brassica: mighty mustard (Brassica juncea), kale (Brassica oleracea var. acephala) and collard (Brassica oleracea var. italica); and the insectary plants were buckwheat (Fagopyrum esculentum) and sweet alyssum (Lobularia maritima).

Kale (Brassica oleracea var. acephala). Photo by David Adreas Tønnessen.*

As a result, the number of herbivores (i.e., crop pests) was larger in the trap crops than in the cash crop. The trap crops were, therefore, more attractive than the cash crops for the pests. The presence of insectary plants increased the number of predatory and parasitoid insects, such as lady beetles and parasitoid wasps, in the trap crops when compared to treatments without insectary plants. The number of parasitized pests also increased in the presence of insectary plants.

Field layout of the study by Shrestha et al. (2019).**

In general, the “team work” of trap crops and insectary plants greatly reduced the influence of agricultural pests on the cash crops. The trap crops attracted the pests to an area close to the insectary plants, allowing the predators to reach them.

Efficient ways to raise crops organically are possible. We just have to focus on a healthy ecosystem and not on money. If we work together, we can defeat the “Big 6” corporations that dominate the food production in the world. They are the real pests.

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Reference:

Shrestha B, Finke DL, Piñero JC (2019) The ‘Botanical Triad’: The Presence of Insectary Plants Enhances Natural Enemy Abundance on Trap Crop Plants in an Organic Cabbage Agro-Ecosystem. Insects 10(6): 181. doi: 10.3390/insects10060181

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

**Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 International License.

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