Ovicidal And Larvicidal Properties Of Crude And Aqueous Guava Extracts Against Aedes Aegypti

2069 words - 9 pages

CHAPTER 1
INTRODUCTION

I. Background of the Study
Mosquitoes are insects in the order Diptera. They usually breed in transient water sources, such as flooded areas, snowpools, and ditches (Rutgers [date unknown]). A mosquito goes through four stages: egg, larva, pupa, and adult. Most eggs hatch into larvae within 48 hours (Biology Notes… 1983).
Mosquitoes are vectors of numerous diseases. Aedes aegypti, a domestic mosquito living in close association with humans, is the primary vector of yellow fever and is also a potential vector of dog heartworm, Murray Valley encephalitis and Ross River viruses (Zettel and Kauffman 2008; Russell 1996). Moreover, it is the principal vector of ...view middle of the document...

Fogging, or space spraying, on the other hand, disperses hundreds of millions of tiny droplets less than 50 μm in diameter into the air. Its efficacy only lasts until the droplets remain airborne (Slideshare 2008). An ovitrap, developed by the Department of Science and Technology, is a black tin can with a piece of lawanit wood stuck inside with a black “organic” solution or chemical developed by epidemiologists. Dengue-carrying mosquitoes gather inside the black container and lay their eggs but the larvae end up being killed in the can (Leyte Samar Daily Express 2010).
On the downside, the outdoor application of aerosol insecticides is costly and ineffective, since the majority of female Ae. aegypti rest indoors to avoid insecticide contact. Moreover, many insecticides are useless due to the spread of resistant mosquitoes (Olson and others [date unknown]). Spraying, although inexpensive and obtainable, enhances resistance of immature stages of mosquitoes to pesticides (Scanlon [date unknown]). Meanwhile, fogging kills adult mosquitoes but not hatchlings. It also causes mosquitoes to flee, transfer to other areas, and become immune to the chemicals used (The Star 2010; Official Gazette [date unknown]).
Another way to effectively decrease the number of diseases transmitted by mosquitoes is through the elimination of mosquito larvae and ova. This said elimination can be done through the use of larvicides and ovicides, which can be chemicals or natural bacteria (Kempraj and Bhat 2008). Killing mosquito ova and larvae before they emerge as adults can reduce or eliminate the need for ground or aerial application of pesticides to kill adult mosquitoes. Currently, larvicides such as Bacillus sphaericus, Methoprene and Temephos are being used. However, in the use of these larvicides, there is an acute and chronic risk to some fish and freshwater invertebrate species. In large doses, these larvicides can cause nausea or dizziness (US EPA 2010; DOHMH 2010). Extracts from neem and Cyperus plants have ovicidal properties. However, they have strong and pungent smells that can cause irritation or nausea (Kempraj and Bhat 2008; Suite101 [date unknown]). Ovitraps such as grass infusions and cyfluthrin, on the other hand, are moderately toxic to mammals and are plain toxic to fish (Singh and Bansal 2005; Extoxnet 2010).
Crude extracts from certain plants have been proven to be effective in killing larvae and ova of mosquitoes. Extracts obtained from Solanum xanthocarpum were proven to be effective biological mosquito larvicides against Culex, while extracts obtained from the fruits of Momordica charantia were found to be larvicidal against Culex, Anopheles and Aedes (Changbungjong and others [date unknown]; Singh and others 2006). Crude extracts from Calodendrum capense were discovered to be larvicidal against Aedes, as well (Kiprop and others 2005).
Other crude extracts were also proven to exhibit ovicidal properties against certain genera of mosquitoes....

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