GARLIC OIL APHICIDE: An Organic Alternative Pesticide for Cotton Aphids (Aphis gossypii) in Guava leaves

GARLIC OIL APHICIDE: An Organic Alternative Pesticide for Cotton Aphids (Aphis gossypii) in Guava leaves

I. INTRODUCTION

A.           Historical Background

Plants have been cultivated and traded since perhaps 8000 BC (Huxley 1978) and insect pests have long plagued humans and their crops. Ancient civilizations recorded swarms of locusts and other insect pestilence (Harpaz 1973, Konishi and Ito 1973). As humans expanded crop cultivation, associated insect problems soon followed. The European colonists of the New World faced their own set of insect-related problems with the cultivation of both native and introduced crops. For example, tobacco, which is native to the New World, experienced insect damage from hornworms and flea-beetles from the outset of its cultivation (Garner 1946). The introduction of new plants also began early during European colonization. Sugarcane was transported from the Canary Islands to Hispaniola on Columbus’s second voyage in 1493 (Deerr 1949). Some of these early introduced plants also had their associated pests, including aphids. The close association of aphids with their hosts meant those insects and their eggs were being transported through commerce as well (Howard 1898). The cabbage aphid, Brevicoryne brassicae (Linnaeus), was noted in North America as early as 1791 (Miller et al. 2006). Early entomologists were well aware that commerce and travel were responsible for the transport of some of these pests. In 1856, Asa Fitch speculated that B. brassicae was brought along with cabbage plants on shipboard cargo (Miller et al. 2006).

            Infestations generally result from small numbers of winged aphids that fly to the plant and find it to be a suitable host. They deposit several wingless young on the most tender tissue before moving on to find a new plant. The immature aphids or nymphs that are left behind feed on plant sap and increase gradually in size. They mature in 7 to 10 days and then are ready to produce live young. Usually, all of them are females and each is capable of producing 40 to 60 offspring. The process is repeated several times, resulting in a tremendous population explosions. Less than a dozen aphid "colonizers" can produce hundreds to thousands of aphids on a plant in a few weeks. Aphid numbers can build until conditions are so crowded, or the plant is so stressed, that winged forms are produced. These winged forms fly off in search of new hosts and the process is repeated. (uky.edu, retrieved March 2014)

B.   Significance of the Study

a.    Human Health

There were not any studies that showed the adverse direct effects of cotton aphids on human health. However, application of harmful pesticides have shown to give negative effects on human health. Thus, it is of much importance for the researcher to find alternative pesticides against cotton aphids without causing damage in the human health. Pesticides can enter the human body through inhalation of aerosols, dust and vapour that contain pesticides; through oral exposure by consuming food and water; and through dermal exposure by direct contact of pesticides with skin. Pesticides are sprayed onto food, especially fruits and vegetables, they secrete pesticides into soils and groundwater, which can end up in drinking water, and pesticide spray can drift and pollute the air. For all pesticides to be effective they must be toxic. Insecticides cause the greatest number of pesticide poisonings in the United States (Lorenz, 2009), but their toxicity can also be harmful to other animals, organisms and the environment. The effects of pesticides on human health are more harmful based on the toxicity of the chemical and the length and magnitude of exposure; Hazard = Toxicity x Exposure (Lorenz, 2009). Insecticides targeted to disrupt insects can have harmful effects on the nervous systems of mammals, due to similarities of vertebrate structure. Organophosphate insecticides inhibit the enzyme cholinesterase causing an accumulation of acetylcholine in the body resulting in uncontrolled neuron transmissions. These chemicals can poison all life forms with cholinesterase in their nervous system, such as insects, fish and birds. The biggest concern when using pesticides should be, how long it takes for these chemicals to fully be degraded . These chemicals can bioaccumulate in the body over time as well as bioaccumulate in animals of our food chain such as fish and chicken. 

b.    Environmental Significance

Harmful pesticides applied on crops can travel great distances through the environment. When sprayed on crops or in gardens, pesticides can be blown by the wind to other areas. This process is called pesticide drift. Water-soluble pesticides can flow with rainwater into nearby streams or can seep through the soil into ground water. This means that the pesticides may run off to other areas and cause damage to un-targeted animals and plants in other places, as well as contaminating our water supply. Many pesticides are soil contaminants that can have an adverse long-term effect. Due to the loss of organic matter and catabolic microorganisms in the soil, there is a decrease in water retention and catabolism of organic substances (Warsi, 2004). On top of this, insecticides that remain in the soil inhibit nitrogen fixation, which is required for plant growth. Insecticides can also have a direct harmful effect on plants such as poor root hair development, shoot yellowing and reduced plant growth (Rockets, 2007).
Some pesticides can remain in the environment for many years and pass from one organism to another. Fat-soluble pesticides are readily absorbed in insects, fish and other animals, often resulting in retention and persistence of pesticides in food. DDT, for instance, is a fat-soluble pesticide and can accumulate in organisms by a process referred to as bioamplification. A small amount of pesticide can be absorbed into bodies of animals lower in the food chain, the higher the trophic level, the greater the concentration of toxins. The top carnivores hence have a highly concentrated level of toxins and negatively influence this population. As a result, the balance in the ecosystem could be disrupted (Warsi, 2004).

c.    Economic Development

In general, aphids reduce crop yield and/or quality, which lead to significant economical losses. 
The major crops infected are wheat, barley, sugar beet, potatoes, lettuce, and beans. The damage caused by aphids depends on the type, for instance the black bean aphid causes damage by direct feeding whereas the green peach aphid causes the most damage by being a virus vector for more than 120 viruses (Rothamsted insect survey).
The average percentage loss caused by different aphid species is variable, ranging from 4,4% on potatoes, since these plants are rather resistant to aphids, compared to 46-43% on field beans. In 1979, aphids caused a potential economic loss of £70 x 106 in Britain. In the US, aphids have an economic impact of more than one-quarter billion dollars in an outbreak year (Larsson et al., 2005).

I.              RELATED LITERATURE and STUDIES

Cotton aphids are small insects (1-2mm in length). They are rounded with long antenna and two distinctive siphunculi at their tail end. Cotton aphids vary between yellow, dark green, brown and dull black. Cotton aphids have winged and non-winged forms. The winged aphids (alates) are all adult females and this stage is highly mobile between crops. Alates are produced if the colony is stressed due to crowding or poor food quality. Alates search for a suitable food source, settle and promptly start producing live young without the need to mate. These young will develop into wingless adults. Female aphids give birth to live female young which are clones of themselves, inheriting all of their characteristics including any insecticide resistance. An aphid can give birth to as many as 6 young per day, which mature into adults in 4-7 days leading to many generations per season. Multiplication can continue until the colony becomes crowded or until suitable plant growth is no longer available which induces production of winged forms able to move and locate new hosts. (www.cottoncrc.org. , retrieved March 2014)

An aphid feeds by inserting its proboscis, stylet or straw-like mouthpart into the phloem or inner cells of a plant. Upon insertion the aphid draws the plant’s juices or sap. This feeding activity will normally cause leaf and stem deformities and it can aid the transmission of various plant diseases, both bacterial and viral, all of which can affect the plant’s appearance and value. If left unchecked, these diseases may even kill the plant. An additional problem that may also affect the aesthetics of the plant include presence of cast skins — a by-product of aphids molting from one nymphal stage to the next (which is occasionally confused by novices as stationary whiteflies since they’re white). Another aesthetics problem, if the population becomes large enough, is the formation of black-sooty mold growing on the sugary, ant-attracting excrement of these pests. This excrement (a.k.a. poop) is known to attract sugar-feeding ants which may, in an effort to manage their food source, herd or physically move aphids and protect them from biocontrols, natural and introduced. This last condition, if the aphid population grows large enough to support ants, can make orgainc aphid control even more challenging. (https://greenmethods.com/aphids/, retrieved March 2014)

Garlic (Allium sativum), like other plants, has an exquisite defense system composed of as many different components as the human immune system. In order to protect itself from insects and fungi, garlic enzymatically produces allicin when it is injured. Thus, allicin is mother nature's insecticide. Allicin was discovered in 1944 by Cavallito et al.¹who first noted its potent antimicrobial activity. Allicin received a patent for its antifungal activity in test tubes. However, no clinical trials have been performed with allicin and it was never developed into a drug or commercial product due to its instability, inability to be absorbed, and offensive odor. Allicin itself is considered to be of limited value inside the body and is presently regarded by the scientific community as just a transient compound which rapidly decomposes to other compounds.

According to infonet-biovision.org, garlic has anti-feedant (insect stop feeding), bacterial, fungicidal, insecticidal, nematicidal and repellent properties.
Garlic is reportedly effective against a wide range of disease-causing pathogens and insects at different stages in their life cycle (egg, larvae, adult). This includes ants, aphids, armyworms, diamondback moth and other caterpillars such as the false codling moth, pulse beetle, whitefly, wireworm, khapra beetle, mice, mites, moles, Epilachna beetles, and termites as well as fungi bacteria and nematodes.

Garlic is non-selective; it has a broad-spectrum effect and can kill beneficial insects as well. Therefore, it should be used with caution. It is not recommended for aphid control since it kills the natural enemies of aphids. Adult ladybird beetles seem not to be affected by garlic sprays (Ellis et al. 1992) (Brooklyn Botanic Garden, 2000). Drenching with garlic extracts to control soil nematodes, although effective, should be avoided since it may also kill many beneficial soil bacteria and insects.

III. STEPS and PROCEDURES

            This experimentation aims to eliminate aphids using organic pesticide to avoid the intake of toxic chemicals by plants which is limited only to the use of guava leaves, at the same time, will not cause damage on plant leaves.

            There were two parts in the experimentation: (1) To test damage on guava leaves (2) To test the effectiveness of the aphicide.

Part I – Leaf Damage Testing

1.    Four setups were put in place, labeled A, B, C, and D. Each setup were placed with a guava leaf without aphids for testing.

2.    The mixtures were the following:

Mixture A: In a spray bottle, mix one cup of palm oil, two cups of water, and two teaspoons of dishwashing liquid.

Mixture B: In a spray bottle, mix one-fourth cup of dishwashing liquid and two cups of water

Mixture C: In a spray bottle, mix half a cup of 70% isopropyl alcohol and one cup of water.

Mixture D: Finely chop two cloves of garlic and soak in one tablespoon of palm oil for 24 hours, then strain. Mix with two cups of water. Pour into a spray bottle.

 E: one cup of water (control)

3.    Spray the mixtures into the assigned setup. Observe within 24 hours.

4.    Repeat procedure no. 3 for trial 2.

Part II – Testing the Effectiveness of the Aphicide

1.    Use the mixtures that did not cause damage on the plant leaf. Label them accordingly. Spray the mixtures equally on each of the infected guava leaf (with aphids). 

2.    Repeat the first procedure for trial 2 with another set of infected guava leaves.

3.    Leave the setups overnight. Observe.

IV. RESULTS

            The following are the results based on the experimentation conducted:

Table 1.1 Leaf appearances after spraying the mixtures:

MIXTURE	QUALITATIVE RESULTS (Trial 1)	QUALITATIVE RESULTS (Trial 2)
A	Oily, with blackened parts	Oily, with blackened parts
B	Blackened and dried up	Blackened and dried up
C	Green, unaffected	Green, unaffected
D	Green with some blackened parts	Green, unaffected
E (control)	Green, unaffected	Green, unaffected

Table 1.1 shows that setups A and B caused damage on guava leaves. Setups C, D, and E, however posted less harm on the plant leaves, and thus qualified to be used on the second part of the experimentation.

Table 1.2 Test results of the effectiveness of the aphicide

MIXTURE	QUALITATIVE RESULTS (Trial 1) Effective / Ineffective	Time	QUALITATIVE RESULTS (Trial 2) Effective / Ineffective	Time
C	Ineffective	-	Ineffective	-
D	Effective	15 seconds	Effective	12 seconds
E (control)	Ineffective	-	Ineffective	-

Table 1.2 shows the test results of the effectiveness of the aphicides. It was qualitatively described as effective or ineffective considering the number of seconds it took the aphicide to kill the aphids on guava leaves. This clearly shows that mixture D proved to have effectively killed the aphids in both trials 1 and 2.

CONCLUSION

Therefore, it has been proven that mixture D, which contained garlic, oil and water, can be an organic alternative to commercially available pesticides. This can be effective in killing aphids without damaging plant leaves at the same time.

RECOMMENDATION

         

            The researcher would like to recommend further studies to be conducted using this aphicide on different plants and other species of aphids. Moreover, the researcher would also like to recommend that certain methods be conducted for mass production of this aphicide for commercial consumption.

References

• ·         uky.edu, retrieved March 2014
• ·         www.cottoncrc.org. , retrieved March 2014
• ·   http://www.infonet-biovision.org/default/ct/232/recipesfororganicpesticides, retrieved March 2014
• ·         http://2013.igem.org/Team:KU_Leuven/Project/Aphid_Background, retrieved March 2014
• ·         https://greenmethods.com/aphids/, retrieved March 2014