M. Dicke et al., Change in behavioral response to herbivore-induced plant volatiles in a predatory mite population, J CHEM ECOL, 26(6), 2000, pp. 1497-1514
Damage by herbivorous spider mites induces plants to produce volatiles that
attract predatory mites that consume the spider mites. A clear attraction
to volatiles from Lima bean plants infested with the spider mite Tetranychu
s urticae has been consistently reported during more than 15 years for the
predatory mite Phytoseiulus persimilis. We have monitored the response to v
olatiles from spider-mite infested Lima bran plants for a laboratory popula
tion of the predatory mite from 1991 to 1995 on a regular basis. A reductio
n in the level of attraction in the laboratory population of P. persimilis
was recorded in mid-1992. The attraction of the laboratory population was w
eaker than that of a commercial population in the latter part of 1992, but
the responses of these two populations were similarly weak in 1994 and 1995
. Therefore, a behavioral change has also occurred in this commercial popul
ation. Experiments were carried out to address the potential causes of this
change in attraction. The attraction of predators from a commercial popula
tion with a strong response decreased after being reared in our laboratory.
Within a predator population with a low degree of attraction, strongly res
ponding predators were present and they could be isolated on the basis of t
heir behavior: predators that stayed on spider-mite infested plants in the
rearing set-up had a strong attraction, while predators that had dispersed
from the rearing set-up were not attracted to prey-infested bean plants. Fr
om our laboratory population with a low degree of attraction, isofemale lin
es were initiated and maintained for more than 20 generations. All isofemal
e lines exhibited a consistently strong attraction to spider mite-induced p
lant volatiles, similar to the attraction recorded for several populations
in the past 15 years. Neither in a population with a strong attraction nor
in two with a weak attraction was the response of the predators affected by
a starvation period of 1-3 hr. Based on these results, possible causes for
the observed reduction in predator attraction to spider mite-induced bran
volatiles are discussed. The predatory mite P. persimilis is a cornerstone
of biological control in many crops worldwide. Therefore. the change in for
aging behavior recorded in this predator may have serious consequences for
biological control of spider mites.