Genetic Control

Methods for genetic control fall into two broad categories: (1) those by which pests are rendered less capable of reproduction and (2) those in which resistance is increased in the organism attacked by the pest. Included in this category is the genetically engineered introduction of microbial toxin genes into plants.

A variety of genetic mechanisms are potentially applicable for regulation of a pest's reproductive capability, including dominant lethality [the basis of the sterile insect release method (SIRM)], inherited partial sterility, autosomal translocations, male-linked translocations, and hybrid sterility [see reviews by Proverbs (1969), Whitten and Foster (1975), Whitten (1985), Steffens (1986), Bartlett, in Pimentel, 1991, Vol. 2; Robinson, in Rechcigl and Rechcigl, 2001)]. To date, however, only one of these, the SIRM, has been used on a full scale; the rest are under examination in laboratories or in field trials, or still at the theoretical stage.

Knipling (1955) first proposed the idea of releasing sterile males into wild populations of the pest so as to reduce total fecundity. He suggested that successive releases of sterile males over a number of generations would lead, cumulatively, to eradication of the pest. To be successful SIRM requires that the pest can be mass-reared and sterilized, usually by irradiation though some chemicals can produce the same effect. The irradiation does not cause sperm inactivation; rather, it causes chromosomes to break, resulting in chromosome imbalance and death of the zygote.

SIRM has been used with striking success against the screwworm fly (Cochliomyia hominivorax), which has been eliminated from large areas of Central and North America, including Curacao, the United States, Mexico, Puerto Rico, Guatemala, El Salvador, Belize, and Honduras (Graham, 1985; Wyss, 2000). Authorities are confident that it is only a matter of time (and political agreement) before the pest is fully eliminated from Central America. SIRM was also used to eradicate screwworm fly in Libya, following its accidental introduction in 1988. Some 1.3 billion irradiated pupae from Mexico were subsequently released, and the last case of screwworm was reported in 1991 (Lindquist et al., 1992).

SIRM has also been used successfully against other pests, for example, Mediterranean fruit fly (medfly) (Ceratitis capitata) in California, Mexico, and Chile, melon fly (Dacus cucurbitae) in Japan and Taiwan, and Mexican fruit fly (Anastrepha ludens) in California. In the latter case a barrier zone of sterile flies in Baja, California and the Tijuana area prevents invasion by the pest. Other SIRM projects, including those against onion fly, mosquitoes, tsetse flies, pink bollworm, gypsy moth, corn earworm, tobacco hornworm, and boll weevil, are being carried out with varying degrees of success (Robinson, in Rechcigl and Rechcigl, 2001; Krafsur, 2002).

The advantages of SIRM are its specificity, the permanency of its effect (though it may take several years to achieve this), and the fact that it does not pollute the environment. An important disadvantage is its limited applicability. For example, it is not feasible to use SIRM on pests that appear sporadically or in high density; the latter would make it very difficult to achieve the necessary high ratio of sterile:wild males in the field. Initially, there were technical problems related to the mass production and/or release of only male

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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