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PLANT
RESISTANCE AND BIOLOGICAL PEST CONTROL The IPM approach most compatible with
biological control is the development of plant resistance (Kogan 1982).
Nevertheless, incompatibilities arise when mechanisms of resistance
indiscriminately affect both pests and natural enemies, or when natural enemies
are indirectly affected through their hosts or prey. Experimental evidence of
incompatibilities is shown in tomato (Duffee & Isman 1981, Duffey &
Bloem 1986, Duffey et al. 1986). This may be illustrated with Heliothis zea, Spodoptera
exigua and the endoparasitic
wasp, Hyposoter exiguae (Vier.). When host
larvae ingest a diet with the glycoalkaloid tomatine, the development of the
parasitoid is detrimentally affected (Duffey & Bloem 1986). Kogan et al.
(1992) warn that such studies demonstrate that depending on the mechanism of
resistance, natural enemies may be detrimentally affected; and that when
exploiting such mechanisms one should weigh the risk of reducing the natural
enemy load versus the benefit of the particular resistance trait. Obrycki (1986) studying the impact of
potato glandular trichomes on Edovum
puttleri (Grissell, an egg
parasitoid of the Colorado potato beetle, drew similar conclusions. He showed
that E. puttleri readily parasitizes L. decemlineata
eggs on Solanum tuberosum but that the
parasitoid is entrapped in glandular trichomes of Solanum berthaultii.
On S. tuberosum, egg mortality is increased not only due to
parasitism but probably also to host feeding and superparasitism. But aphid parasitoids
that are equally affected by S.
berthaultii trichomes in the
greenhouse were not greatly affected in the field, showing that moderate
levels of trichomes and the biological control of potato aphids are not
incompatible. Therefore, it is apparent that both biochemical and physical
plant defenses are potentially detrimental to natural enemies. As behavioral
adaptations of parasitoids of insects adapted to resistant lines may occur in
nature, it would be useful to identify such adapted populations when
searching for new sources of natural enemies (Kogan et al. 1992). [ For
further details, please see <bc-49.htm> ] REFERENCES: <pooled.htm> [Additional references
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