Tropical Gardening: Long hot summer sees plant and people pests increase

We are on our way to coastal Colombia and for sure preparing ourselves for all the tropical diseases to which we might be exposed.

Zika, dengue, malaria and other tropical mosquito-carried diseases are in the news more and more. However, that is just the tip of the iceberg so to speak.


If you think insect problems are getting worse, you might be right, but some insects have been giving us trouble for a long time.

Insect populations come and go in cycles. These depend on many factors including temperature, moisture, food supply and predators. In Hawaii, our climate seems to be getting warmer every year, with record highs constantly being broken.

Several examples of these cycles can be observed in your garden.

With warmer weather, you will see some increase in plant-sucking insects such as aphids. You can actually increase the aphid population by applying excessive amounts of nitrogen so the plants grow lush and tender. If you fertilize with a balanced, slow-release fertilizer, you are less likely to have a population explosion of aphids. Also, if you have lots of insect-eating birds, lizards and frogs, this helps keep the problems down.

From the beginning, man has been prey to the lusts and appetites of hordes of insects. Very early in history, humans devised methods of combating these pests that bugged them.

More often than not, manual dexterity in the form of slapping and picking was the prime instrument of insect control. In the course of development, humans learned that some substances applied to the body discouraged insect aggression.

Applying a grease coating to the skin was one method. Another was to never take a bath. This originated the idea of repellents. If you are planning camping or hiking trips, the use of an insect repellent is a must, so let’s learn something about them.

Early repellents consisted largely of plants or plant products, though animal products also were employed. The earliest chemical repellent in widespread use was Bordeaux mixture for plant diseases. Pliny recommended a mixture of red earth and tar to repel ants.

It is also known that the Greeks and Romans painted the backs of parchment manuscripts with cedar wood oil to prevent injury by insects. Parts of the neem tree have been used for thousands of years in India as insect repellents, but also have fungicidal and bactericidal properties.

There are many other natural repellents such as lemon eucalyptus oil, citronella, lemon grass and garlic. It was not until after the end of the 19th century that chemical repellents were marketed in the West.

More than 9,000 chemicals have been tested as repellents for mosquitoes and other biting flies, chiggers, fleas and ticks but only a few have proven effective and also safe for general application to the skin or clothing. Some of the effective materials have little or no odor and give almost complete protection for two to eight hours as skin-applied repellents and for several days for repellents applied to clothing even in areas where insect populations are high.

Toxicologists conducted extensive tests with off-the-shelf repellents and found them safe for use as skin applications. They can be toxic if taken internally.

Occasionally, there are people who are allergic to certain materials that passed toxicological tests. Such people might show a slight rash or other minor skin reactions. Any of the repellents can cause some smarting when applied to the mucous membranes or areas where the skin is especially tender, such as the eyelids.

A repellent must be uniformly distributed over the area to be protected, for the insects will discover and bite in any small area that is not covered.

The most common method of using a repellent is to shake a few drops from the bottle or spray from the pressurized can into the palms, smear evenly and then apply thoroughly the backs of the hands, wrists, neck, ears, face or other exposed skin, much as in washing. Sufficient repellent should be applied to give a uniform film.

Most of these repellents feel oily to the skin and might be objectionable to some individuals. However, the protection they afford from biting insects more than compensates for this oiliness.


Under favorable conditions, one treatment will last several hours on most people. Clothing properly treated with any of the repellents will give protection for several days.

With all the mosquito- and tick-born diseases such as Zika, Chikungunya, dengue and tick fever, it is important to protect ourselves and our loved ones. Gardening and traveling are fun, but if bugs are bugging you or your plants, repellents are the first line of defense.

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