Dealing With Insect Pests
Insect pests cause harm by damaging and destroying crops, as well as by spreading disease. Current methods of controlling destructive insects have had at best limited success.
Chemical insecticides can be effective in reducing insect populations, but they become less effective over time due to the targeted insects developing resistance to the chemicals used as a result of natural selection. Furthermore, the insecticides are also toxic to beneficial insects, such as honey bees used for pollination, as well as other species, including humans.
Biological control has the advantage of narrowly targeting the insect pest species without the collateral damage to other species and the environment resulting from chemical pesticides. Biological control depends on finding a natural enemy of the targeted species in order to keep the population of the latter in check. A limitation of biological control is that while it can reduce the population of the insect pest, it cannot completely eliminate it. Additionally, caution must be observed to ensure that the species used as the biological control agent does not itself become a pest by preying on species other than the intended pest.
Another method of insect pest control involves releasing sterilized males into the targeted population. For this technique to be effective, the number of sterilized males released must be at least comparable to the number of normal males in the population, and the females of the species must mate only once. However, even under these conditions, the targeted population will be reduced but not eliminated and will grow back to its previous size in a few generations.
An approach that appears to have great potential for eliminating insect pests was described by Crow (1979). He reported experiments in which a mutation was created on the Y (male) chromosome of Drosophila melanogaster, commonly known as the fruit fly, which caused males to produce exclusively male progeny, with that trait being passed on to those progeny. Since only half of the progeny produced by normal males are males (the rest being females), it follows that if some male-producing males were to be introduced into a normal population, the ratio of male-producing males to normal males would double each generation. Since the number of females is equal to the number of normal males, and the overall population is constrained by the available food supply, the male-producing males will eventually overwhelm the normal population, and then they too will vanish due to the lack of females. This experiment was actually done, with the expected results: Introducing a few male-producing males into a normal population caused that population to become extinct after several generations.
A similar experiment involving male-producing males was attempted using Aëdes aegypti, the yellow-fever mosquito. Unfortunately, in this case, the genome contained genes that diminished or nullified the effect of the male-producing mutation. However, the technology to manipulate genes has advanced considerably since the time that this research was reported, such as by the use of CRISPR, so it might be possible to engineer a male-producing mutation that would resist the effects of the inhibiting genes.
The use of male-producing males as a means of pest control could also be applied to rodents (mice and rats), although due to the longer lifespan of rodents, as compared to insects, it would take years, rather than months, for this method to be effective.
Reference
Crow, J. F. (1979). Genes that violate Mendel’s rules. Scientific American 240(2), 134–43, 146.