Biology Reference
In-Depth Information
eral of which are of conservation concern (Pemberton 2000). We shall
examine this phenomenon in detail in chapter 17.
Evolutionary Adaptation by Introduced
Insect Arthropods
Most studies of alien herbivorous arthropods have concentrated on
applied topics such as developing methods of control and counteracting
evolution of resistance to chemical control. Arthropods have shown an
extraordinary ability to evolve new genetic races in the agricultural envi-
ronment. More than 500 species have evolved resistance to insecticides, in
many cases exhibiting resistance to several major chemical groups of
insecticides (McKenzie 1996). For example, the diamondback moth
(
Plutella xylostella
), an insect pest of various crop plants of the mustard
family in tropical and subtropical areas, has evolved resistance to every
chemical pesticide used against it and also to the bacterial pesticide,
Bacil-
lus thuringiensis
(Talekar and Shelton 1993). Evolutionary adaptability in
response to strong selective pressures, such as those imposed by several
pesticides, has also been shown by many vertebrates, including fish,
amphibians, birds, and mammals. Recently, for example, European rabbits
(
Oryctolagus cuniculus
) resistant to sodium monofluoroacetate (compound
1080) were found in southwestern Australia (Twigg et al. 2002).
Experimental evidence has shown that many herbivorous arthropods
have the potential for rapid evolution of new host plant relationships
(Jaenike 1990;Via 1990). Gould (1979), for example, examined the poten-
tial for host plant adaptation by the two-spotted spider mite (
Tetranychus
urticae
), an herbivorous species known to feed on more than 180 species
of host plants. Mites collected from the wild were reared for 8 months on
bean plants that were a favorable host for the species. At this point, the
mite population was divided into two groups, one that continued to feed
on bean plants, and one that was given a combination of bean and mite-
resistant cucumber plants. In this experiment, the availability of bean
plants in the bean and cucumber mix was manipulated so that mites were
forced to feed exclusively on cucumber for periods of up to 3 wk. Dur-
ing this time, their populations declined and selection for individuals most
able to feed on cucumber occurred. The experiment was continued for
21 months. Results showed that mites in the bean and cucumber popu-
lation improved substantially in survivorship and fecundity. When sur-
vivorship was tested at the end of the experiment on the most toxic
cucumber leaves, for example, mites from the bean and cucumber popu-
