Two Kinds of Parasite Reproduction

The reproduction of most crop parasites is either sexual or asexual. The majority of insect parasites of crops have sexual reproduction only, while the fungi imperfecti, bacteria, and viruses have asexual reproduction only. However, most fungi, and some insects (e.g., aphids), have both kinds of reproduction.

Parasites that have both kinds of reproduction are typically those of discontinuous pathosystems, and the different functions of the two kinds of reproduction are clear. The function of the asexual reproduction is to produce a very rapid r-strategist population explosion, in order to exploit the ephemeral food supply of a discontinuous pathosystem. The function of the sexual reproduction is genetic recombination and the maintenance of variability. Typically, this sexual reproduction occurs before the start of a discontinuous epidemic. This ensures maximum heterogeneity in the parasite population at the start of the epidemic. This heterogeneity is needed when each parasite individual has the problem of finding a matching host individual in a vertical subsystem (see 4.14 & 4.15).

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