Table of Contents
What is Leaf-cutter ant?
Leafcutter ant or tribe Attini is a species of ant that is found in abundant in American tropics. These ants are easily recognized as their foraging columns are made of hundreds or even thousands of ants that carries small leaves. The stretch of the moving ants can reach up to 30 metres. It can be found in areas where there is forest cover or tree canopies.
Usually, the leafcutter ants clips the pieces of leaves on the transports it to an underground nest that have over a thousand chambers. These chambers house over millions of ants both young and adults. Depending on the size of the ants, each lives at different castles that are in the chambers. For instance, workers, reproductive, guards and soldiers live each in their own respective castes. More also, leafcutter ants chemically and physically cultivate what is referred to as ‘subterranean gardens’ deep within the nest. This garden is a result of growth of fungus on the chewed leaves.
The ants also have a mechanism of removing contaminants from the gardens. They do this by producing amino acids and enzymes which aid in fungal growth. Also, they produce substances that are known to suppress fungal growth of specific species. Additionally, different species of ants grow different types of fungi. However, all these fungi belongs to family Lepiotaceae. They also belong to genus Leucoagaricus or Leucoprinus commonly referred as leucocoprinaceous fungae.
The unique aspect of leafcutter is the cultivated fungi that is found in their nests. The cultivated fungi is helpful to the entire colony as it provides them with food from the fungal strands. More also, from protein-containing bodies known as gondylidia. Leafcutter ants workers depend on plant sap while the larvae depends on fungus.
Usually, new colonies are hatched in rainy season and this is when queens which carries fungal rubbles disband in remarkable mating swarms. However, in other genera of ants, the pattern of fungus transmission is not yet clear. One of the dominant herbivores of New World tropics is leafcutter ant. According to a new report, it is estimated that about 15% of all leaf production is cut by leaf cutters ants. These species may not be desirable due to the fact that they reduce commercial value of pasture land.
On the positive side, leafcutter ant stimulate new plant growth after vegetable pruning. Also, by gardening the fungal food, the ants waste enrich the soil. The large nests of leafcutter ants are usually found in trees that are far apart and with little underground.
General Appearance of Leafcutter Ants
Leaf cutter ants are rusty or dark-brown in color. The workers also range in different sizes despite being of the same colony. The size of these ants is about 1/16 to ½ inch long. However, the queen leaf cutter ant is approximately ¾ inch long. A leaf cutter ant body has three pairs of prominent spines that is found in its thorax and a pair that is found on the back of its head. It has several different species and one of it is Texas leaf cutter ant.
In a colony of leaf cutter ant, there are 4 or 5 queens which constantly churns out eggs that hatch into a population. These eggs develop into larvae that is cream in color and it is about ½ to ¼ inch long on full development. The ant has mandibles which appears as steak knife with serration which enables it to cut through leaves.
How to Kill Leaf-cutter Ants Effectively?
1 Chemical Control
This is one of the highly applied method of eliminating leaf cutter ants. These insects are considered as a nuisance especially when they infest agricultural land. Despite being small in size, they can clear acres of land within a span of days and cause massive destruction. More also, they also destroys flowers and other plantation around residential areas and hence they presence is not desirable. Therefore, looking for a better way to control them is very important taking consideration the financial losses associated with them.
Use of chemicals to control leaf cutter ants is more effective in terms of coverage area and residue content. Chemicals in the market are being manufactured in such a way that they will remain in the soil for some time to ensure that there is complete destroying of the eggs. Usually, to achieve effective chemical control, it is important to apply the chosen chemical pesticide 50 to 60 days before soil preparation or harvesting.
This is because, seedling are more susceptible to damage by the leaf cutters as they are soft. Therefore, by ensuring that the planting area is free from the leaf cutters, there will be no damage experienced. Carrying out surveillance in the first month of planting is necessary especially after buds starts to appear. This should be followed by treatment for about four months.
If the area being controlled is a tree plantation, after about 2 years where maintenance stage has been reached, chemical control should be carried out once or twice a year especially in the dry season. However, there should be constant surveillance to ensure that there are no signs of infestation. Sampling of the relationship between nest area and number of holes should be carried out and this determines the dose to be used. Sampling also determines spatial distribution of nests as colonies are concentrated at forest edges and this allows for effective control without the need to control the entire area.
The commonest active ingredient in pesticides that controls leaf cutter is fipronil, sulfluramid, fenitrothion and deltamethrin. The main formulations include dry powder, granulated baits and fogging. More also, a fogger machine can be used. Baits are usually more used as there are operational, economical and practical. It uses an attractive ingredient such as dehydrated citrus pulp or any other organic material. Baits may not however been used in wet season as the ingredient will be dissolved in water and get wasted.
Fogging is another effective chemical control measure. However, it is relatively expensive and this is due to cost of equipment maintenance. To get the best results, the active ingredient should be mixed with diesel or kerosene and introduced directly into the nest in form of smoke. The method is appropriate before planting when it is easier to physically identify the nests. To apply the product, spearheading directly into the nest is carried out. Additionally, there are plant extracts which control leaf cutter ants that can only be introduced by fogging and this include d-limonene.
Dry powder is another form of chemical control of leaf cutter ant. This is usually applied directly into the active nest holes by use of dusters. However, this method is slow and only effective over a small number of nests. It should also be used in dry season as the powder absorbs water rendering it ineffective. It also makes it difficult for the dry powder to penetrate into the soil.
2 Plant Resistance
Plant resistance is another way through which leaf cutter may be controlled. This means that one can chose to deal with plants that are known to be naturally resistance to leaf cutters. This is especially encouraged in the regions where there is massive infestation of leaf cutters and using other methods such as chemical control will be costly. This is a biological method of control and more recommended when one is dealing with organic farming which involves growing of crops without use of pesticides. It also minimizes the negative impact use of chemical have on the soil. More also, beneficial soil microbes will not be affected when the pesticides are applied to the soil.
An example of a plant that is known to be resistant to leaf cutter is Eucalyptus species. Research has shown that density of leaf cutter ants found is Eucalyptus plants is relatively low as compared to other tree species. Some of the factors that results to this resistance include physical, chemical and mechanical factors.
3 Mechanical Control
This is another method that can be used to control leaf cutter ants. It involves excavation of leaf cutter nests and capturing of queens and destroying them. The queen lays eggs and therefore by destroying them, it can result to extinction of the entire colony. This method is however recommended to be used 4 or 5 months after nuptial flight as at this period, the queens are found 20 cm deep in the soil. This is considered as one of the oldest method to control leaf cutter.
Mechanical control and in particular excavation is tedious and no convenient. Moving from one area to the other looking for nests will not only use more time but result into fatigue. More also, it may be difficult to cover the area entirely without leaving some nests identified. In terms of convenience, the method may not be used when plantation is already growing as it results to disruption of root system. However, this is an effective method when one has a small orchard. Another way to achieve mechanical control method is by applying of plastic tape coated with grease, strips or aluminum and plastic cylinder, metal or plastic which are fastened around the tree trunks. This is only effective for a small trees or flowers as it cannot be effective for large scale farm. More also, it is effective to use only in season where leaf cutter are more active due to weather conditions. For instance, during winter season, the leaf cutter are not active and trees are not blossoming so there is less destruction that will be experienced.
4 Biological Control
This involves use of living organisms to control leaf cutters. In a research done, it showed that entomopathogenic fungi Metarhizium and Beauveria bassiana which were tested against leaf cutter ants reduced greatly its population. Using baits that contains these pathogens, reduced the population by about 20 to 72 per cent. More also, an isolate of M. anisopliae is found to be pathogenic to leaf cutter ants. A mortality of over 75% was recorded in the first three of application.
Biological control when mixed with chemical control has been recorded to be very effective. For instance, upon applying a pesticide with imidacloprid at low concentrations with B. bassiana, it increases the susceptibility of the leaf cutter ants and changes their behavior. Fungus Paecilomyces farinosus is also reported to greatly reduce the population of leaf cutter ants.
Advanced research is being carried out in this field to ensure that biological control is more effective. This is due to the benefits that are associated with biological control of pests. Unlike a method such as use of pesticide, it is more environmental friendly. More also, due to increased awareness on organic farming, it provides a way for pest to be controlled without having to rely on pesticides. However, there is still some challenges being experienced when it comes to biological control. One of it is the fact that pests with time become resistant and develop mechanisms to defend themselves. These ants with time develop special behaviors for instance disposal of symbiotic fungus and also infected ants. Also, they develop morphological features for instance a cuticle sclerotisation that forms a protective barrier, anal hairiness and infrabucal cavity to protect themselves against the invading pathogens.
Another aspect of biological control is endophytic fungus which are found on leaves that reduces foraging of leaf cutter ants. This is due to low volatility compounds which are released after wounding of the trees. Manipulation of the environment also favor ant’s natural enemies. For instance, increasing diversity between strips of native vegetation and Eucalyptus. Certain insects, birds and native mammals for instance wasps and beetles are natural enemies of leaf cutter ants and therefore their existence in an ecosystem contributes to control of the colonies. They are also numerous diurnal predators of leaf cutting ants.
5 Cultural Control
By use of varying plant species as substrate for the symbiotic fungus, leaf cutter ants are polyphagia’s. One cultural leaf cutter ant method is by ensuring that vegetative material is used far away from their nests and this reduces the impact on agricultural sector. Alternate cropping, crop rotation and carrying out different sowing dates is some of the way to achieve this. Use of natural phosphate fertilizer also reduces damage that is caused by these pests.
Plowing is another cultural control method which is carried out within 4 months of nuptial flight. More also, at this time, the queen are found about 20 cm deep. Applying pesticides during land preparation effective when plowing is deep as to reach and overturn the leaf cutter ant nests. Minimum tillage is a method that is largely adopted by foresters as it reduces soil disturbance but have been shown to contribute to increased leaf cutting ant nests.
Combining growing of plants such as castor, grass species, sesame and sweet potato with culture also serves as a trap food that have repellant or deleterious effects on leaf cutter ants. Some plants are also toxic to these pests and their symbiotic fungus. Certain natural pesticides are also known to interfere with the ant’s behavior for instance β-eudesmol derived from eucalyptus leaves. Some also triggers aggressive behavior or confuse when it comes to recognition within the nests.
Symbiotic fungus of leaf cutter ant acts as a mediator of ant nutrition and this is by hydrolyzing plant polysaccharides. The fungus produces large amount of enzymes which the ants feed on and release their waste on the garden as fecal fluids. This in turn digests the plants tissues. The association between the symbiotic fungus and leaf cutter ants is very important for their survival as it enables them to draw nutrients from the plants they bring into the nest. Therefore, destroying of the symbiotic fungus a good way of controlling the survival of leaf cutter ants. There are natural products which are toxic to the symbiotic fungus. For instance, Leucoagaricus gongylophorus, Canavalia ensiformis, Helietta puberula and Simarouba versicolor. These are introduced in form of baits with plant extracts. This cultural control method is effective and stops the activity of leaf cutter ants for about 3 to 12 days upon application. To achieve effective control of these measures to control leaf cutter ants, ensure that proper land preparation is achieved. This will greatly minimize the need to constantly control the pests.