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(Hagler and Cohen, 1991). When P. mac-
uliventrisand Podisus sagitta(Podisus nigrispi-
nus) were returned to a diet of live prey after
more than 15 generations on artificial food,
the predators did not show any difference in
their predation capacity on Spodoptera exigua
larvae and had similar developmental and
reproductive rates to those of predators
maintained on live prey (De Clercq and
Degheele, 1993). After three to four genera-
tions on a meat-based artificial diet, P.
nigrispinus nymphs and adults exhibited
prey-capture abilities comparable to those
reared on housefly larvae, in both laboratory
and greenhouse assays (Saavedra et al.,
1997). Some workers have even reported
greater predation rates for diet-reared preda-
tors than for their prey-fed peers.
Chocorosqui and De Clercq (1999) found
that, despite their smaller size, nymphs of P.
maculiventris reared on artificial diet had
killed significantly more S. exigualarvae on
sweet-pepper plants after 24 h than had con-
trol insects fed live prey. After 96 h, however,
this difference had disappeared. Greater
aggressiveness of diet-reared predators has
also been noted for nymphs of P. nigrispinus
by Saavedra et al.(1997) and for adults of D.
tamaniniiby Castañe et al.(2002). It is worth
noting that the above predation studies were
mostly done using simple laboratory arenas,
in some cases not even involving host plants.
Given the complexity of the field situation,
predation rates measured under unrealistic
laboratory conditions should not be extrapo-
lated to the field. In this respect, more
research is needed to evaluate the influence
of tritrophic factors on the searching abilities
of predators (and parasitoids) reared on
unnatural foods.

Parasitization rate (see also above)

The parasitization rates of T. dendrolimiand T.
chilonisreared in vitroare similar, 65 and 68%,
respectively (Feng et al., 1999), but these rates
are lower in artificially than in naturally
reared T. pretiosumand T. galloi(Consoli and
Parra, 1996), as well as in Anastatus japonicus
(Han et al., 1988). After ten generations cul-
tured in vitro, Trichogramma minutumfemales
parasitize more host eggs than in vivo-reared

insects (Nordlund et al., 1997). Under field

conditions, mortality induced by in vitro- and

in vivo-reared C. grandisare similar (Morales-

Ramos et al., 1998). Field efficiency is usually

evaluated by the number of hosts parasitized,

but it is also necessary to include host stinging

and host feeding, which could be an impor-

tant mortality factor in specific host–parasitoid

complexes, such as in Trichogramma spp.

(Shipp et al., 1998). Nevertheless, parasitiza-

tion rates obtained in the field are also closely

related to the conditions in which the releases

were conducted (Bigler, 1994).

Host localization, walking and flying

Flight activity and walking behaviour (walk-

ing speed) were tested to compare different

strains of Trichogrammadeveloped in vivo

(Cerutti and Bigler, 1995; Dutton and Bigler,

1995; Dutton et al., 1996). Dispersal activity

and host localization are a key parameter for

Trichogrammaquality, which could be tested

in a special chamber or maze (Honda et al.,

1999). These parameters still need to be

tested for in vitro-produced insects.

Genetic parameters

Long-term rearing of Lixophaga diatraeaein the

laboratory on the alternative host G. mellonella

induced modifications of some biological

characteristics, such as puparial size and

developmental durations (Pintureau and

Grenier, 1992) and of the capability to develop

on artificial diet (Grenier and Pintureau, 1991).

Long-term rearing under laboratory condi-

tions, especially when using artificial diets,

could lead to genetic bottleneck effects and

impose severe selection pressures on the pop-

ulation of an entomophagous arthropod. The

concomitant loss of genetic variability is often

believed to lead to a loss of quality in the nat-

ural enemy. In sensitive species, strong genetic

(and non-genetic) effects are expected to arise

during the very first generations grown in arti-

ficial conditions. The size and heterogeneity of

the founder population usually declines dur-

ing the colony initiation, as described in fruit

flies by Leppla (1989) (see also Chapters 6 and

7). In particular, elevated selection pressure

Quality of Artificially Reared Biocontrol Agents 125