Survival rates of the different developmental
stagesThe survival rates of both T. pretiosumand T.
galloireared on artificial diets are lower than
those of individuals reared on natural hosts
(Consoli and Parra, 1996). The larval density
could be critical in influencing general qual-
ity parameters, such as size, or survival in
the case of cannibalism. Oophagous para-
sitoids cannot regulate the quantity of food
ingested, so the number of parasitoids devel-
oping per unit of food is a key parameter for
development success (see above; Grenier et
al., 1995; Dahlan and Gordh, 1997).
Although rearing on artificial food has
variable effects on the fecundity of insect
predators, hatchability of eggs produced by
artificially reared individuals is generally
similar to that of conspecifics fed insect prey
(Hassan and Hagen, 1978; De Clercq and
Degheele, 1992; Adams, 2000b; Arijs and De
Clercq, 2001). Only Rojas et al.(2000) and
Wittmeyer et al.(2001) have reported lower
viability of eggs laid by females of P. biocula-
tusand P. maculiventris, respectively, on arti-
ficial diet. When assessing egg viability of
predators, however, one should take canni-
balistic activities of adults into account. Both
Cohen (1985) and De Clercq and Degheele
(1992) have noted egg cannibalism by diet-
fed adults of G. punctipesand Podisusspp.,
respectively. The degree of egg cannibalism
will evidently depend on adult rearing den-
sity, but in Podisuseven females reared in
isolation have been seen to feed on their
own eggs.
Nymphal or larval survival was com-
pared among diets in a number of predatory
insects and results often depended upon
predators being reared individually or in
groups. In Podisusspp. survival of nymphs
fed either artificial diet or live food was
equally good when the predators were
reared individually (90%), but when they
were reared in groups cannibalistic activities
reduced nymphal survival to 55–75% (De
Clercq and Degheele, 1992; De Clercq et al.,
1998a). Hassan and Hagen (1978) and Cohen
and Smith (1998) reported survival rates of
Chrysoperlaspp. that were similar on artifi-
cial diet and on flour-moth eggs. In both of
these studies, however, larvae were reared
individually. Despite individual rearing of P.
bioculatusnymphs in multiwell tissue-culture
plates, nymphal survival on artificial food
was inferior to that on frozen Colorado
potato-beetle eggs (Rojas et al., 2000). Group
rearing of O. laevigatuson a number of meat-
based diets yielded similar to slightly lower
survival rates compared with controls fed E.
kuehniellaeggs (Arijs and De Clercq, 2001).
Percentages of cocoons of D. introita
developed in vitrowere not different from
those obtained on pupae of S. frugiperda
(Greany and Carpenter, 1998), and could not
be increased by adding some conditioned tis-
sue-culture media (Ferkovich et al., 1999).
The emergence rate of adults is a quality
control criterion used for in vivocomparison
in Trichogramma(Cerutti and Bigler, 1995).
The emergence rate of both Trichogramma
dendrolimiand Trichogramma chilonisreared in
vitrois 90% of that reared in vivo(Feng et al.,
1999). The percentage of adult emergence of
the tachinid fly E. larvarumobtained either in
vivo(in G. mellonella) or in vitrois quite simi-
lar (Dindo et al., 1999).
Emergence rates of T. dendrolimiare lower
in artificial diets without insect components
than in diets with haemolymph, but results
are variable according to the strain tested
(Grenier et al., 1995). Emergence rates of D.
introitaon an artificial diet developed by
Greany and Carpenter (1998) were similar to
those on host pupae (Carpenter and Greany,
1998). Supplementing the diet with condi-
tioned tissue-culture media or certain host
lipid extracts did not improve emergence
(Ferkovich et al., 1999, 2000).Sex ratio and association with symbionts
The sex ratio is a quality criterion used in
Trichogramma (Cerutti and Bigler, 1995).
Wolbachia is a well-known Rickettsiaceae
that strongly interferes with ‘normal’ sex-
ratio determination in many arthropod
species (Werren, 1997; Stouthamer et al.,
1999). For entomophages the main effects
are cytoplasmic incompatibility and thely-
tokous parthenogenesis in Hymenoptera
and male killing in Coccinellidae. Contrary
to some statements (Consoli and Parra,Quality of Artificially Reared Biocontrol Agents 121