relation between the occurrence of crystals
and the presence of microsporidia, rickettsia
or virus-like particles in P. persimilis
(Bjørnson et al., 1997).
A permanent change in the foraging
behaviour has been observed in a laboratory
and a commercial population of P. persimilis
(Dicke et al., 2000). This change consisted of a
reduced level of attraction to odours emanat-
ing from prey-infested lima-bean plants. As
this odour response plays an important role
in host location in the field, it is expected
that predators with a lower odour response
are less effective for controlling spider-mite
populations. Several hypotheses that may
explain this behavioural change have been
tested. Strong evidence has been found to
support the hypothesis that the behavioural
change is a symptom of an infectious disease
(Schütte et al., 1998; Dicke et al., 2000). The
behavioural change is a contagious phenom-
enon. Contact with dead conspecifics and
their products originating from a population
with a low odour-response level induces a
reduced odour response and higher mortal-
ity in predators originating from a normal
population (Schütte et al., 1998). Maintenance
of a population with a high odour response
in the laboratory is possible only when strict
hygienic rearing protocols are followed
(Dicke et al., 2000). A prominent symptom in
adult female P. persimilis from a population
with a low odour-response level is the pres-
ence of birefringent excretory crystals out-
side the excretory and digestive tract,
predominantly in the legs. The presence of
crystals in the legs is associated with
reduced fecundity, a lower degree of attrac-
tion to prey-infested plants, and predator
death (Schütte et al., 1995).
Predatory insects (various unrelated
taxonomic groups)Aphidoletes(Cecidomyiidae): predators of
aphidsFUNGI.The entomopathogenic fungus
Entomophthora apiculatawas recorded from
Aphidoletes aphidimyza(Rondani) in a green-
house in the southern part of Finland
(Kariluoto, 1981). The midges were used to
control Myzus persicae (Sulzer). The same
fungus was isolated from A. aphidimyza
released in experimental cages outside the
glasshouse. Primary conidia measure 27.3 ×
32.4μm.
During a field study in southern
Germany and Switzerland, three ento-
mopathogenic fungi were isolated from dead
individuals of Aphidoletes thomsonii. B.
bassiana andIsaria farinosa were isolated from
larvae, whereas Entomophthora sp. was iso-
lated from larvae and adults (Smirnoff and
Eichhorn, 1970).Chrysoperla(formerlyChrysopa) (Neuroptera:
Chrysopidae): predators of aphidsVIRUSES.Chrysoperla(L.) is a known host of
two viruses: a cytoplasmic polyhedrosis and
a nuclear polyhedrosis virus (Martignoni
and Iwai, 1981). The effects of these viruses
on the efficacy of Chrysoperlais not known.PROTOZOA.The microsporidium Pleistophora
californica has detrimental effects on the
lacewing, Chrysoperla californica Coquillett.
The lifespan and egg production of infected
individuals are greatly reduced. However,
the microsporidium has no effect on the
lacewing’s host, the potato tuber moth,
Gnorimoschema operculella (Zeller) (Finney,
1950).FUNGI.Several entomopathogenic fungi
affect Chrysoperla carnea(Stevens). C. carneais
susceptible to B. bassianawhen placed under
temperature, starvation or nutritional stress
or a combination of these stresses. The effect
that B. bassiana has on C. carnea varies
according to the age and gender of the host
(Donegan and Lighthart, 1989).
When nitrogen is removed from the diet,
the resulting nutritional stress causes a dis-
ruption of larval development and a signifi-
cant increase in adult and larval mortality.
Under these circumstances, the effects of B.
bassiana on C. carnea are intensified.
Starvation has a greater effect on the larval
stages and it is thought that differences in
susceptibility are due to larval feedingPathogens of Natural Enemies and Pollinators 143