Insects (class Insecta)
The most diverse and numerous in terms of species number of all animal classes, Insects are everywhere around us. Their small size is a main cause of ignorance to their existence but they are in fact the key to the terrestrial micro fauna, as well as providing the basic food source for many higher vertebrates. They come in many forms and usually the adults and larvae are distinct in appearance. Accidental introductions that developed into pests are common, and there are many viable examples otherwise that has caused significant ecological concern.
eg 1 Cactus Moth
Order: Lepidoptera (Butterflies and Moths)
Family: Pyralidae
Scientific name: Cactoblastis cactorum
The Cactus Moth is an unwanted biological control, the most ironic and illustrative example of the true misplaced nature of non-native organisms.
The grey-brown Moth may look slightly haggard, but the caterpillars are a colourful vermilion-orange with black spots all over the body. Up to a hundred eggs are laid in a long chain attached of a spine of the cactus plant. The hatched larvae burrow into the cactus, eating it up in the process. After the food supply is exhausted, Cacoblastis larvae turn to other Cacti until it is time for them to mature into pupae. Affected Cacti, or Prickly Pears, show explicit wormholes and piles of excreted materials nearby where the caterpillars have been feeding.
Around the 1990s the Cactus Moth has been accidentally transported to the Florida Keys from the Caribbean Islands, where it has been introduced as a biological control agent of Prickly Pears (See entry for Prickly Pear). Upon arrival to the Eastern seaboard, the Moth is steadily working its way up towards the Southwestern states along the Gulf Coast. In Florida the Moth has caused severe damage to ornamental Cacti, but the impact has been minor as the Cacti are themselves exotic to the Southeast. However the arid Southwest and Mexico depends on the Cacti as major cash crops and many depend on them for food, pharmaceutical drugs, fodder, export (as ornamental plants or otherwise), and production into other useful products. The Cacti are also environmental keystones in the desert areas, being the habitat for many Birds and Mammals, and a universal food source in many respects. It also stabilizes sandy soil and prevents erosion. Cactus industry yields Mexico over $100 million per year, and Prickly Pear Cactus is a National cultural icon. If the Moths arrive as scheduled to the Southwest, environmental and economical disaster is sure to ensue: currently the Moth is spreading at a stunning rate of 100 miles annually since the new millennium began.
Mexico plans to adopt manual removal of egg sticks if the Moths invade, and the necessity will depend on the development of the expected invasion. Various strategies, including releasing sterilized male Cactus Moths, are expected to be implemented in response to the Cactus Moth's expansion, which is still under way and gaining momentum.
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eg 2 Asian Tiger Mosquito
Order: Diptera (Mosquitoes and Flies)
Family: Culicidae
Scientific name: Aedes albopictus
Mosquitoes are a successful insect group that is notorious for transmitting many diseases that are fatal to humans. Mosquito females feed on the blood of many vertebrates to obtain the rich source of protein so as to produce their eggs, while males are mostly frugivorous. The Tiger Mosquito often occurs in association with other Mosquito species, but it remains relatively abundant. Originating from the Oriental Region, tropical areas of the Pacific and Indian Ocean islands, through to the subtropical regions of China and Japan, the Tiger Mosquito has been introduced into North America through the exports of used tires, in which they nestle comfortably in the water puddles collected in depressions. Now the species has almost attained global distribution --- reaching into the remote South Pacific Islands and Hawaii. Compounded with many of the fellow Mosquitoes of the genera Culex, Toxorhynchites, Trichoprosopon, Uranotoenia and Armigeres, the army of Mosquitoes that has colonized most of the world with the advent of human beings is carrying many lethal viruses that cause such diseases as the Dengue fever, Malaria, Encephalitis, and many more, threatening human health. Other species are also sometimes affected, and these assaults tend to be devastating, as in the avian malaria that broke out in the Hawaiian lowlands.
The prominent silver bands on top of glossy black scales are a distinguishing feature of Aedes albopictus. Its larvae, which are less conspicuous, occur in virtually any water-filled site on the ground, in streams and ponds, flowerpots, cemetery urns, buckets, tin cans and so on in urban areas. Studies have shown that females prefer to lay her eggs in dark-coloured substrates. Depending on the climate, the eggs laid may have the ability to over-winter before hatching, and eggs have been found North of the ice point isotherm in the US. They have remarkable environmental tolerance, and can survive through the larval stage in water sources merely 5mm deep. After hatching the larva can mature in 10 days and metamorphose into a pupa. The blood-feeding adults soon began their journey in the world, and they are diurnal raiders with pronounced crepuscular activities, feeding on the blood of humans as well as domestic animals. Its generalist feeding behaviour gives it the potential to become highly effective pathogen vectors, which is the reason they are now causing so many infections worldwide. Effective control methods are lacking, though other Mosquito larvae may prey on the larvae of the Tiger Mosquito. Mosquito control workers are still fighting with this tough opponent - though not to much avail.
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eg 3 Africanized Honey Bee (Killer Bee)
Order: Hymenoptera (Bees and Ants)
Family: Apidae (Bees and Allies)
Scientific name: Apis mellifera scutellata
Honey Bees are highly prized for their marketable product, honey, which is used all over the world. Humans, having come up with the idea to rear Bee colonies in Bee farms and exploit their natural food stores to the utmost, have introduced the species worldwide in order to satisfy local demand. It is due to the same reason that they are popular that A. mellifera have become harmful non-indigenous species in some areas such as Australia. The African subspecies, A. mellifera scutellata, has also been introduced to Brazil in 1957 to help reinvigorate the Bee farming industry there --- the European strain did not seem to acclimatize well. Subsequently, the members of several colonies were accidentally released and they have since been hybridizing and spreading from South America northwards, leading to horrendous adverse effects.
Worker Bees are 2cm long, brownish with indistinct black bands over the body, and has 4 wings and 6 legs --- as in most other insects. The African subspecies is especially adaptable and infiltrates natural forests, plantations, grasslands with suitable nesting sites, agricultural areas, and notably urban areas and disturbed territories. Despite their limitation to the tropics and subtropics, as in their native environment of Africa, they have managed to spread at astonishing velocities as they nest in practically any site with reasonable shelter and food sources around, even in buildings, rock piles as well as in natural trees, dead logs and so on.
The African subspecies is an effective pollinator and harvest more honey in general. This has wide-ranging effects on native pollinating species as their food source is disrupted by the presence of these Honey Bees. Bee farms using the benign European strain also suffer loss, as Killer Bees are able to eliminate the queen and take over these colonies. Though morphologically similar to their European cousins, Africanized Bees are far more aggressive and defensive of their nest sites, and more readily absconds from old sites when the environmental resources are depleted or are in shortage for some time. They swarm frequently and disperse readily. During times of nectar abundance reproductive swarms may disperse from old colonies every 6 weeks, so mobile are the colonies.
Since their escape from Bee Farms the Killer Bees have spread through over Mesoamerica to California and sweeping across to Texas. Their aggression has caused deaths of humans and other large vertebrates that have been regarded as intruders, often at a distance of more than 10m away. The Bees also harm local Bee Farms as they are hostile to humans and few workers are willing to harvest their honey. Ecological impacts include reproductive failure in some flowering plants due to the removal of other pollinating insects by competition, and indeed the decline of the insects themselves, often very important in the native micro fauna.
eg 4 Fire Ants
Order: Hymenoptera (Bees and Ants)
Family: Formicidae (Fire Ants)
Scientific name: \
Fire Ants obtain their name from the fiery stings they are capable of inflicting on enemies. They belong to the Tramp Ant group, consisting of mostly inherently invasive species, which causes ecological damage in introduced areas without natural predators and congeners to control their numbers. Many of these species have been transported away from the native lands of South America as biological controls or by accident. The Ants' competitive nature enables them to disrupt food webs by dominating food resource; human-aided dispersal is invariably successful due to their adaptability. Colonization is very rapid, and there is no prospect of controlling some of the unleashed species again in the near future.
The group includes the Big-headed Ant, Argentine Ant and others. We will look at two species that have particularly well documented invasion histories.
• Big-headed Ant (Pheidole megacephala)
Probably the most invasive of all Invertebrates, the Big-headed Ant, or Brown House Ant has achieved global distribution. It is an agricultural and domestic pest, and its mutualistic relationship with some phytophagous insects enables the population of these pests to increase out of proportion and destroy crop plants in large amounts.
The Brown House Ant is believed to originate from South Africa, but is now widespread throughout the world in the temperate and tropical areas. It prefers moist, shady environments, and human disturbance does not deter its expansion but in fact favours it. As a result they are found in many habitats including agricultural areas, forests, urban areas, shrublands, wetlands, coasts, and plantations.
Big-headed Ants have many small spines on various parts of the otherwise smooth and shiny exoskeleton, and ranges from yellow to reddish-brown and dark sepia in colour. They average 3mm in length. Reproduction occurs with insemination of the fertile Queen by a male in the colony, which dies after its mission; it is a climate-regulated event, but generally occurs year-round. Queens are capable of laying 292 eggs per month. The eggs take several months to mature through larvae and pupae stages, and the lifespan of workers vary inversely with increasing temperature; at 27°C the lifespan is at least twice as long as when the ambient temperature is at 21°C.
The House Ants are generalists and scavengers, feeding on almost anything they could get their hands on, like small vertebrates, seeds and other insects. They have been found to aggressively other native Ants. High concentrations of this species have shown to lead to declines of vertebrate numbers, probably due to direct predation and competition for food sources, especially with insectivorous animals whose food supply is largely reduced by the presence of the Ants. Apart from harvesting seeds of native plants these Ants are also responsible for aiding exotic plant dispersal, which tend to further endanger native flora. The negative impacts on human habitation include their proclivity to chew on telephone cables and electric wires.
Since movement of soils used in gardening has been found to disperse this exotic species, the effective pre-emptive measure would be to take great care in such transactions and practicing quarantine. Chemical control is by far not environmentally acceptable, with many of the chemical that has been used, for example the notorious DDT and heptachlor, which also damages native wildlife. The most efficacious bait by far is called 'Amdro', and more work is being done on this score to explore about better methods of application.
• Red Imported Fire Ant (Solenopsis invicta)
Native to Southern Brazil and Paraguay, this small colonial Ant, only measuring 4mm long on average, is reddish-brown in colour. It has several related species in its native range with which it coexists with, and a mutual control of population through competition is at work here. These generalist feeders forage in high densities, and can fiercely defend their mound when predators threaten them. Fire Ant stings are highly painful, with pustules developing soon after the attack, which can take several weeks to heal. This effective chemical defense keeps many larger mammals at bay, and the Fire Ants consequently will not hesitate to sting people, domestic animals and other wildlife whenever they feel menaced. Omnivorous, Fire Ants feed opportunistically on invertebrates, plant seeds and rarely scavenge or harvest honeydew from specialized insect species in their native ranges, but have proved to be one of the most detrimental introductions ever.
Colonies of Fire Ants can contain as many as 400000 workers. There are two types of colonies; members of monogyne colonies defend their single mound vigorously and these colonies can achieve a density of 680 per hectare. Polygyne colonies allow Workers to move between mounds freely, and as many as 2600 mounds per hectare has been recorded. Natural dispersal is attained through the emigration of winged Ants, and colony members have the ability to disperse on flowing water, which allows them to disperse to a great distance away during seasonal flooding by congregating into a huge lump when waters levels rise, when they can sustain themselves for weeks before reaching the shore.
Since the introduction of the species to the United States in the 1930s, the Fire Ant has successfully colonized 110 million hectares. As recently as 2001, the Fire Ant has also been found in Australia, where the notorious potential of these Ants towards damaging local ecosystems are causing widespread concern. They are catholic in habitat choice and can be found anywhere apart from swamps and closed forests, and do not shun disturbed areas such as roadsides, pastures and lawns in cities. Attracted to electrical equipments, they have caused short-circuits in various appliances including computers, initiating fires in extreme cases.
Fire Ants are particularly horrendous amongst the exotic species in North America for they affect virtually all members in the trophic levels of ecosystems, and native wildlife are under multiple siege. Seed dispersal carried out by native Ants is thwarted by Fire Ants, as they relocate and eat many of these plant seeds. They feed largely on fruits and nectars, burrow into the stems and kill off many insect pollinators, affecting the survival of many plants. They also have large effects on the invertebrate fauna, and replace many of the higher invertebrate predators as the dominant predator on many ground-dwelling arthropods. All stages of development of the insects which Fire Ants prey on are attacked, from egg to larva and adult; even top predators within the micro fauna, such as spiders, succumb to predation from Fire Ants. Well documented affects in birds, particularly ground-nesting species such as the Bobwhites, and small mammals suffer decline as Fire Ants attack their young --- stung juveniles suffer from reduced weight gain, troubled vision, loss of phalanges and immobility. High Fire Ant densities have been found to cause the emigration of some Vertebrates, which restricted their ranges and reduced their populations. Population collapse of the Texas Horned Lizard and other Reptiles are associated with the deprivation of food source due to Fire Ant predation. Fire Ants like to attack nests and eggs and young of Turtles, Lizards, Alligators, and Birds; in the infested range, Cliff Swallow, King Snake and Mississippi Alligator populations are affected by these sordid grim-reapers.
The astonishingly high fecundity of these minute killers has prevented most eradicative measures from staging any effect. Noxious chemicals, for example hydramethylnon and S-methoprene, which inhibit insect growth, have been implemented in destroying some colonization attempts on small scales, but the poison also annihilated the native invertebrate fauna and was not eco-friendly. In places where recent inadvertent introductions have been made --- Auckland and Brisbane in particular, quarantine and poisoning have been practiced in hope of preventing the Fire Ants from spreading into the natural habitats and threatening native wildlife, just as they did in the Southern States. Eradication attempts in Brisbane have cost $123 million, and $300 million annually in US are spent in Fire Ant control. Yet whether this highly ferocious pest will succumb to human control still remains to be seen.
• Yellow Crazy Ant (Anoplolepis longipes)
This Crazy Ant is also called the Long-legged Ant due to the presence of long legs and antennae, and its common name is well chosen, describing its frenetic behaviour when confronted. Workers are slender, reaching 5mm in length, and are yellowish-brown with black markings and a darker belly. It does not sting but sprays formic acid to deter predators and stun their prey, in some cases causing irritation to the yes and skin of farmers in the field. This species can be found in almost any suitable habitat from forests, plantations, grasslands, agricultural land and urban areas.
The origin of the Yellow Crazy Ant is at best speculative as it has been so widely introduced around the Tropics that the whole equatorial belt of Africa, South-east Asia and many Indo-Pacific Islands has been invaded. The highly predatory nature of the Ants inspired agriculturalists to attempt to exploit it as a biological controlling agent against pests of coconut and cocoa. Highly generalist, the Ants find abundant resource in the plantations into which they have been transported, and they forage for pest species and native beneficial species alike day and night. They are not choosy about nesting site requirements, construction of nests under leaf litter, burrows excavated by other invertebrates, crevices in soil and even the base and crowns of tropical trees in the plantations have been documented. In coconut plantations they survive well on the nectar produced by coconut palm flowers and the honeydew of some scale insects. Their broad diet also includes all kinds of soil invertebrates and canopy life, while larger vertebrates are not immune as well. In particular they have developed mutualistic relationships with homoptera scale insects producing carbohydrate-rich honeydew, the Ants harvesting the nutritious droplets and offering protection to the scale insects on the trees they live --- this allows the scale insects to proliferate and disturbs the ecological balance as the scale-insects are generalist herbivores that can defoliate the canopy when their population rises above a certain critical level.
The negative impact of Crazy Ants is not as trivial as that; they are ruthless predators on many of the keystone species endemic to tropical areas, affecting Birds, Mammals and Reptiles alike, altering the community structure and trophic relationships that can cause fragile ecosystems to collapse. The Ant also opens up scope for secondary invasion. For example, on Christmas Island the invasion of African Giant Snails and many shade-intolerant noxious weeds have succeeded that of the Crazy Ants, as the ecosystem structure is sufficiently weakened to give reduced competition, increased food sources and more space for new invaders to further undermine the ecosystem.
Easily transported in soil, the species have been found to travel in long-distance aircrafts, lorries and container ships to many seaports in Australia, where the Ant has never been found before. They thrive in packaging material and timber and thus are hard to detect, and inadvertent introductions might have been made.
Supercolonies extending over a range of 150 hectares, and colonies expand during wet seasons. Worker Ants are produced continually but the rate of production fluctuates quite a great deal. Control measures have been wanting, but researchers are mapping Crazy Ant territories on some islands so that chemical baits can be introduced in order to eliminate this pest. Low level of intoxicants are used, in the hope that affected workers will bring the toxin back to the colony and eradicate the Queens, the reproductive pillar of a colony.
eg 5 Asian Longhorn Beetle
Order: Coleoptera (Beetles)
Family: Cerambycidae (Longhorn Beetles)
Scientific name: Anoplophora glabripennis
A large beetle reaching 3cm in size with very long, pied-banded antennae, the Longhorn is native to the Far East, in China and Korea. Its range has expanded in China, where it has become a severe pest of hardwood trees, which they bore holes in and kill. Recently many incidences of interception of Long-horned Beetles have been documented in the US; in the Central Park of New York, as well as Chicago, the infestation of trees has begun. Despite the fact that large-scale outbreaks of this pest has not yet realized in the US, it is expected that some of the established populations are expanding quickly, which may eventually lead to uncontrollable disaster of the native forests and ecosystem collapse due to the loss of hardwood trees such as maple, elm, horse chestnut, ash, birch, poplar, and willow.
Longhorn larvae are white grubs that after hatching within 15 days of egg-laying, burrows into the centre of the woody trunk to develop by feeding on healthy tree tissues, and pupate to mature as adults, which then creates round exit holes on the trunk when escaping. The adults then tend to stay on the host tree to feed but may disperse short distances. Longhorns kill trees by disrupting tree sap flow, which is the source of nutrient of the trees, and can potentially disrupt the energy flow in forest ecosystems.
Unlike many exotic organisms though, an effective control on the Beetle has been found and is being experimented on with considerable success. The pesticide named imidacloprid is being used in small infestation areas in Central Park. It is injected into the tree and transported throughout the tree via the circulatory system, and kills the grub and adults alike. However this is harmful to the tree and is implemented currently on small scales only to curb further spread of the Longhorn.