Biology Reference
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different groups ( Rickettsia , Spiroplasma , Flavobacteria, and Wolbachia ) identi-
fied ( Majerus and Hurst 1997, Hurst et al.1999a,b, Majerus et al. 1999, Hurst and
Jiggins 2000, Sokolova et  al. 2002 ). Coccinellids may be especially susceptible
to invasion by and establishment of male-killing microbes due to their biology.
Coccinellids feed on aphids and lay eggs in tight batches, which promotes sib-
ling-egg cannibalism and significant levels of mortality of newly hatched larvae
due to starvation ( Majerus et al. 1999 ).
The evolution of male killing may have evolved because the bacteria are
almost exclusively transmitted vertically from mother to eggs. As a result, bac-
teria in male hosts are at an evolutionary dead end, so male killing has a fit-
ness cost of zero from the bacterial point of view ( Randerson et  al. 2000 ).
Furthermore, the death of male embryos could augment the fitness of the
remaining female brood by providing food to those females carrying the clonal
relatives of the male-killing bacteria ( Randerson et al. 2000 ). However, Majerus
and Majerus (2010) found that resistance to a male-killer can develop, suggest-
ing that there is an “arms race” between host and microbial symbiont.
10.14 Sex and the Sorted Insects
Resolving the molecular genetics of sex determination in arthropods and learn-
ing how to modify sex ratio or fertility will have both theoretical and applied
applications, and could lead to improved genetic control of pests or useful
genetic modifications of beneficial biological control agents.
10.14.1 Genetic Control
Genetic control of pest insects represents an attractive alternative to chemi-
cal control in terms of safety, specificity, and the limited negative impact it has
upon the environment. The screwworm ( Cochliomyia hominivorax ) eradication
campaign demonstrates what can be achieved with mass releases of males ster-
ilized by irradiation ( Box 10.1 ). The principle of sterile-insect releases has been
applied to other pests, including the Mediterranean fruit fly ( Ceratitis capitata ),
tsetse flies ( Glossina palpalis and G. morsitans ), mosquitoes ( Anopheles albima-
nus ), codling moth ( Cydia pomonella ), and ticks ( LaChance 1979 ).
Sterile-insect release programs usually require only males, but both sexes typi-
cally must be reared. Not only is it expensive to rear large numbers of “useless”
females, but, in the case of species that vector disease or annoy or bite humans
or domestic animals, it is undesirable to release any females, sterile or not! As
a result, genetic methods have been used to develop “genetic sexing strains,”
strains that make it easy to separate males and females. For example, slight
differences in size or color of pupae have been used to sort out undesirable
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