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Impact of Non Native Insects on Agricultural Ecosystems

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Using examples, describe how invasive, non-native insects can affect agricultural ecosystems and "wild" ecosystems in areas outside their native range


The global climate is changing rapidly and this trend is expected to continue throughout and beyond the 21st century. Rising temperatures as well as new precipitation patterns are toady affecting different aspects of natural world and human society worldwide. Indeed, we are experiencing many changes as a result of climate change in the ecosystems on an astonishingly pace and scale. Non-native species are thought to be of greatest threats as a result of the current global warming. There are almost approximately two thousand established invasive species in Britain. Indeed, the factor of non-native species cost Great Britain approximately £1.7 billion annually. As each species have their way of responding to these changes in environment, its interactions with the physical world as well as the organism around it change too. This causes a cascade of influence within the entire ecosystem. In fact, such influence can lead to a spreading out of species into new areas, interaction of different species to a point of species extinctions. This paper aims to examine and describe with examples how invasive or non-native insects can impact agriculture ecosystems and wild ecosystems in areas outside their naive range.

Non-native insects also referred as exotic, non-indigenous, alien, or introductions are insects introduced to new areas or living outside their native distribution range as a result of human activities, either deliberate or accidental. According to Krueger and May (1991) non native species can be described as the transfer of different organisms outside their native range. Different type of animals have been transferred or transported to different locations as a result of different means and introduced into new areas for many years. Many of these introductions have been both accidental and intentional, however, many have not. For intentional, the primary reason is for agriculture or livestock production such as domesticated cattle, honeybees, goats, swine etc.

Invasive species either large or small have devastating impact on agricultural ecosystem and wild ecosystem in areas outside their native range. According to Schowalter and Whitmore (2002) invasive insects are one of the major threats to native wildlife and other plantations worldwide. In fact, approximately 42 percent of endangered or threatened species are at risk mainly as a result of invasive species. Agricultural ecosystems are also at high risk from invasive species. The effect of invasive insects on our agricultural products cost billions of dollars annually.

An invasive species are many type of living organism-an amphibian, insects, plant, bacteria, fungus or eggs that are not native to an ecosystem and has the potential to cause harm to the environment. However, for the purpose of this paper, we shall examine the species insect as the invasion species. Insects in non-native areas have the potential to harm the environment especially the agricultural ecosystem. They do grow and reproduce rapidly and hence spread in a hostile way, with the potential to cause harm and thus, they are labeled as "invasive".

It is important to understand that invasive insects might not come from a different country.

According to Wittenberg and Cock (2001), invasive species such as insects pose great threat on biodiversity across the globe. However, insects from a large part of the invasion fauna across the globe appears to have received excessively less attention regarding their impact on the agricultural and wild ecosystem compared to aquatic or vertebrate organisms (Levine et al. 2003; Long 2003). Nevertheless, according to Jenkins (2003) through direct interactions, invasive insects have the potential to affect native biodiversity, for instance, a herbivore feeding on a native plant that wild animals are supposed to feed on. Evans (2006) note that the migration of insects to a new location has the potential to attack native prey or host. Additionally, invasive insects has the potential to affect native species as well as ecosystems indirectly through cascading impacts or other several mechanism such as the spread of diseases, competing for space and food (NRC, 2002).

Invasive insects can particularly be harmful to native plants populations. Nevertheless, many publications examining ecological impacts of non-native insects do not appropriately quantify these effects. However, the most documented effects on invasive species are undoubtedly these caused by insects on agriculture and wild ecosystems. According to Mallet (2005) hybridization between native ecosystems and invasive insects is a major concern as a result of disturbances that can produce in native genetic resources. Indeed, hybridization has been established in plants and in many cases has continued to show a negative effect on native species (Long 2003).

In particular, North America has been largely been affected by invasive insects that are said to originate from Europe. For instance, the balsam woolly adelgid, A. piceae, (pictured below 1) as well as the hemlock wooly adelgid, A. tsugae, are said to pose threat to forest ecosystems in Northern America through killing Fraser fir and Carolina hemlock, Tsuga Canadensis on a large scale (Small et al. 2005). As shown in image 2 below:

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Image 1: balsam woolly adelgid, A. piceae

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Image 2: hemlock wooly adelgid, A. tsugae,attackingFraser fir and Carolina hemlock

Another example is the gypsy moth,Lymantria dispar (image 3 below)as well as the hemlock woolly adelgid, Adelges tsugae,is seriously affecting the hemlock and oak forest in North America (Orwig and Foster, 1998). Another example of invasive insects threatening agriculture is the scale insects Orthezia insignis, which are seriously threatening endemic gumwood (Fowler, 2004) and the ambrosia beetle Xylosandrus compactus that are attacking a number of vegetations in Hawaii.

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Image 3: gypsy moth,Lymantria dispar

Since their accidental introduction to North America from Europe, around mid 19th Century, the gypsy moth (L. dispar) has become major pests that affect trees in Eastern North America (Liebhold et al. 1995). Additionally, Eurasian insects have also caused serious issues for many trees in America and Europe including the spruce aphid, Elatobium abietinum image 4 below (Lynch 2004), as well as the recently introduced emerald ash borer, which in the past few years has affected over 15 million ash trees (Poland and McCullough 2006).

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Image 4: Spruce aphid, Elatobium abietinum attacking a plant

By reducing or killing the host plant populations, invasive insects also have the potential to impact many other native plants species. According to Gray (2011), the bugs which were introduced accidently in Britain from other countries are at this period considered as the greatest threat to many garden plants. Plants such as rosemary and sage, lilies and fritillaries flowers and shrubs like berberis are today under attack from invasive insects. Many insects have been confined to attack plants in the south east of England. As a result, many horticulturalists have monitored the spread of insects such as Scarlet lily Beetle (Lilioceris lilii) image 5 below, Rosemary Beetle, Hemerocallis gall midge (Contarinia quinquenotata), and Berberis sawfly (Arge berberidis) have warned that the insects have the potential to spread quickly northward and westward across Britain devouring plantations (Gray, 2001).

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Image 5: Scarlet lily Beetle, Lilioceris lilii attacking a leave

The Royal Horticultural Society (2016) has described the invasive insects as "most wanted" pests and they are urging farmers to be on the lookout. The organization continues and said that the spread of these insects is quite worrying as they defoliate the plantations and spoil the flowers. Even though they do not kill the plants they leave the weakened to a point that they cannot grow properly. Climate change is the main cause of this move as summer got hotter and winter milder, it has cause insects that were in the south of England to migrate and spread further north. These insects (Scarlet lily Beetle, Rosemary Beetle, Hemerocallis gall midge, and Berberis sawfly) are among the increasing number of non-native species that are causing devastation across the England landscape.

One of the common insect is Rosemary Beetle (Chrysolina americana) that has spread quickly attacking herbs such as sage, lavender, rosemary and thyme. The image below shows Rosemary Beetle:

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Image 6: Rosemary Beetle

As they establish themselves in the new environment, invasive insects in Canadian forests such as Lepidoptera, Hymenoptera, and Coleoptera engage in competitive and trophic interactions with native species and hence potentially impacting natives through several direct and indirect mechanisms (Gandhi and Herms 2010). Invasive insects such as phytophagous feed on native woody plants and thus compete with native species for space and food and they also consume native insects and parasitoids. As well as direct interactions such as interference competition and consumption, non-native insects might therefore interact with native species through other mechanisms such as indirect mutualism, trophic cascades, and exploitative competition (White et al. 2006).

According to Lovett et al. (1995) this interactions are most of the time considered to be negative. However, there are some beneficial of mutuality interaction with naïve species. For instance, the impact of interactions between natives and invasive might occur are different levels of ecological organization such as the level of the gene, population, ecosystem, community and individual (Parker et al. 1999).

As discussed above, the introduction of invasive insects such as gypsy moth (Lymantria dispar) is most of the time described as one of the most destructive ecological species in North America forest (ISSG 2009). According to Gale et al. (2001) the defoliation of Gypsy moth opens up the canopy, reduces the growth of trees, kills and weaken trees' outright and as well as alter nutrient cycling and ecosystem processes in the forest. At the long run, gypsy moth invasion can also lead to changes in stand composition and structure. These effects of gypsy moth on forest can cause both lasting and temporary changes in habitant for other organisms in the forest such as birds and mammals (Schowalter and Whitmore, 2002)

Invasive insects' causes harm to wild ecosystems in many different ways. When a new and aggressive species are introduced to a new ecosystem, it can breed quickly as well as spread, taking over the plants and the location. As a result, native wildlife might fail to provide any protective mechanism against the invader as the species has no predators. Invasive insects are said to have devastating effects on an ecosystem and it might result to the local extinction of native species, particularly if they are endangered. When invasive insects are introduced to a new area outside their range it is likely that they will disrupt the natural food web and as a result start to compete with the native wild ecosystem and directly predating them. In this view, when natural food pattern are disturbed, the results becomes complex and varied consequences, which later lead a reduction in biodiversity within the habitant.

The gypsy moth defoliation effect on canopy openness lead to understory plant growth, tree mortality and stand composition that has some impact on wildlife. Increased openness of canopy can in one way reduce populations of bird's species that are linked with closed canopies

The effects of gypsy moth defoliation on canopy openness, understory plant growth, stand composition, and tree mortality can also have impacts on forest wildlife. Increased canopy openness can temporarily reduce populations of bird species associated with closed canopies Gale et al. 2001, as well as cause nest predation. Equally, increases in understory cover and dead trees have been considerably linked with increased profusions in the eastern towhee (Pipilo erythrophthalmus) as well as cavity-nesting bird species.

Moreover, species that stay in an open canopy are more in defoliated stands (Bell and Whitmore 1997). This means that gypsy moth defoliation leads to an increased habitat complexity, which at the other case can be beneficial for forest birds and wild animals in the ecosystem.

3.1 Parasitism on native fauna

Invasive insects have also the potential to affect that native fauna as a result of parasitism on native vertebrates or insects. In many cases, parasitoids have been applied as biological control means nationally. In just a few cases, these control measures have turned to be a threat to non-target insects. One of the best know example in forest ecosystem is that is tachinid fly, Compsilura concinnata, which were introduced in North America from Europe at the start of 20th century to control gypsy moth, which is today suspected to have a negative effect on populations of endangered natives (Boettner et al. 2000). Also, according to Bildfell et al. (2004) alien ectoparasites of vertebrates have the potential to threaten native species. For instance, a chewing louse, Damalinia sp., can cause hair-loss effect in black tail deer in western North America.

3.2 Competition

Additionally, competition is likely to occur between non-native insects and native animals for nesting areas. Hybridization between invasive and native species can as well occur, which leads in reduced fitness of offspring and could eventually result to the extinction of the species. Moreover, invasive insects can introduce pathogens into the new area, which has the potential to spread to the native ecosystem which has not experienced the disease there before and thus they have no immunity to it. In additional to diseases being transmitted to flora and fauna, other many diseases that come with insects can as well be transmitted to nearby human population.

Invasive insects are said to affect communities and populations of native area through competing for same resources (Reitz and Trumble 2002). The Asian adelgid (Pineus boerneri Annand) have shown some competitive nature that has resulted to displacement of native congener in red pine plantations in Eastern parts of the U.S, through the reduction of host plant quality forcing the native animals to less suitable locations (McClure, 1989). Also, the European weevil (R conicus) act of feeding on flower-heads of native animals in the U.S. considerably reduces the density of native tephritid flies, which also are said to feed on flower-heads (Louda et al. 1997).

Also, according to Roque-Albelo (2003) the scale insect kill endangered plants populations in the Galapagos, has also led to local extinctions of host-specific Lepidoptera.

Several ecosystem processes can also be altered by invasion insects such as nutrients and water cycles, habitant and succession modification, which later result to a reduction of biodiversity. Indeed, altered water cycle can result to an increased risk of flooding within the area. In additional to be associated with high scale ecological impact, invasive insects can as well have some economical implications. For instance, the government of U.K often spent approximately £1.7 annually in the control of pests (Wild Screen Arkive, 2001). In fact, direct economical losses might occur from non-native insects' causes serious damage to infrastructure or goods and indirect losses leading from decreased tourism in affected area.

3.3 Spread of Vectors of diseases

Invasive insects might also be a source of several vectors or facilitate the transmission of both plant and wild animal diseases. According to Brasier (2000), the European bark beetle, Scolytus multistriatus, is known to be a common source of the Dutch elm disease in North America. The European beech scale, Cryptococcus fagisuga is linked with the fungus ectria coccinea var. faginata, which causes beech bark illness (Houston 1994). Additionally, the invasion mosquitoes are also vectors of avian malaria that affect endemic birds in the forest ecosystem in Hawaii (LaPointe et al 2005).

Above all, invasive insects also play an important role as pollinators in the flowering plants. Many of the plants especially flowers are dominant producers in several terrestrial ecosystems, but there is no way they can reproduce without insect intermediaries in order to carry pollen from one flower to another. Plants in the ecosystem produce an array of colors, rewards, odors, as well as ruses in order to attract their insect accomplices. Any flower grows in a design that ensures no insect visitor leaves without a thorough dusting of pollen, which is destined to another flower nearby. Therefore, invasion insects have the capability to continue transfer of pollen to anther flower and thus ensure continued populations of plants.

Despite the fact that many of the remarkable studies focuses on ecological effects of invasive insects in the forest ecosystem, there is a still neglected scope that would merit further attention. In conclusion, this paper has clearly indicated that invasive or non-native insects have the potential to affect agricultural ecosystems and wild ecosystems in areas outside their native range through several mechanisms. Several examples have shown that invasive insects affect growing plants and wild animals in the ecosystems. As it has been established in this paper, non-native insects can impact biodiversity through direct interactions such as herbivore feeding on native plantations. The other effect is a predator or a parasitoid attack on native wild or host. Moreover, there invasive insects hybridize with native species. It is also established that invasive insects may affect communities and plant populations of native herbivores through competing for the same resources.

In addition, this paper has established that invasive insects can affect vegetation and wild ecosystems indirectly. This can occur through cascading effects or other mechanisms such as carrying diseases, competing for space and food as well as sharing natural enemies with native ecosystems species. Moreover, it has been established in this paper that ecological effect by invasive insects can happen at different levels of biological organizations such as genetic impact- effects on populations, communities or individuals of species. The invasive insects effect on the processes of ecosystems in both agriculture and wild animals.

Finally, invasive alien insects have been considered to be one of the most significant threats to biodiversity across the globe. In fact, invasive insects are seen top threaten many native ecosystems by consuming, competing and displacing them. However, a number of governments are investing huge amount of dollars to attempt to find solution to already devastating and devouring small animal that is destroying millions of vegetations and wild worldwide.


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