All parameters related to reproduction are
important, and sometimes reproduction
capacity can be estimated by a simple mea-
surement, such as the body size of the para-
sitoid, as in Encarsia formosa(van Lenteren,
1999). In predators as well, body size is often
believed to be a good predictive index of
fecundity, but the relationship between the
two parameters is not always clear. For
instance, females of the predatory pentatomid
Podisus maculiventrisreared on an artificial
diet were significantly smaller than those fed
larvae of Tenebrio molitor, but their fecundities
were similar (De Clercq et al., 1998a). Rojas et
al.(2000) obtained females of Perillus biocula-
tuson artificial diet with similar size to that of
those offered Leptinotarsa decemlineatalarvae,
but their fecundity was only 10% of that of
prey-fed controls. Establishing a relationship
between the size and predation capacity of a
laboratory-produced predator has been
shown to be even more problematic, even
when it is produced on live prey (e.g. De
Clercq et al., 1998b). Cohen (2000a) reported
that Geocoris punctipesreared for over 6 years
on artificial diet were significantly smaller
than feral specimens but had similar preda-
tion capacities. Chocorosqui and De Clercq
(1999) found that, despite their smaller size,
artificially reared nymphs of P. maculiventris
even showed significantly greater predation
rates than prey-fed controls.
Several morphological traits and develop-
mental and reproductive parameters that
have been used to assess the quality of artifi-
cially reared parasitoids and predators will
be reviewed below. For clarity we shall treat
the most widely used parameters separately,
but, where applicable, links between differ-
ent traits will be discussed.
Morphological parametersSize or weight of different developmental
stagesSize or weight of eggs deposited by in vitro-
reared natural enemies has only rarely been
monitored. Fresh weights of eggs laid by
females of the heteropteran predators G.
punctipes and P. maculiventriscultured on
bovine meat diets were similar to those of
eggs from females maintained on insect prey
(Cohen, 1985; De Clercq and Degheele, 1992).
Only occasionally have workers monitored
fresh weights of larvae during their develop-
ment on artificial diets. Nevertheless, such
studies may reveal where nutritional deficien-
cies are most crucial. Larval weights of preda-
tors fed on artificial diets have often been
found to be inferior to those of their prey-fed
peers (Hagen and Tassan, 1965; Hussein and
Hagen, 1991; Chocorosqui and De Clercq,
1999; Wittmeyer and Coudron, 2001).
Puparial weight was surprisingly higher in
the tachinid fly E. larvarumreared in vitroon
artificial diets than in vivoin G. mellonella
(Dindo et al., 1999). Availability of food ad libi-
tumin artificial rearing might explain this
result. Vanderzant (1969) also reported greater
pupal weights for artificially reared lacewings,
Chrysoperla carnea, compared with controls fed
Sitotroga cerealellaeggs. Hassan and Hagen
(1978) succeeded in rearing larvae of C. carnea
on an artificial diet and obtained pupae with
similar weights to those in controls fed moth
eggs. Likewise, no difference was observed
between pupal weight of Chrysoperla rufilabris
fed a meat-based artificial diet and those fed
Ephestia kuehniella eggs (Cohen and Smith,
1998). Pupal weights of the colydiid beetle
Dastarcus helophoroidesreared on artificial diet
were not different from those of predators
reared on live prey (Ogura et al., 1999), but
pupal weights of in vitro-reared Trogossita
japonicawere only half of those of beetles
reared in vivo(Ogura and Hosada, 1995).
In both parasitoids and predators, adult
body weight and size have often been used
to evaluate the effectiveness of a diet (see
above). Adult weights of D. introitadevel-
oped in vitrowere lower than those of indi-
viduals fed host pupae (Spodoptera
frugiperda), and they were not significantly
improved by adding some conditioned tis-
sue-culture media (Ferkovich et al., 1999), but
they were improved when the diet was sup-
plemented with certain host lipid extracts
(Ferkovich et al., 2000). Usually larger hosts
produce larger wasps showing a greater egg
load and a higher longevity, as described in
the encyrtid Metaphycussp. (Bernal et al.,
1999). As in many insects, puparial weight in
tachinid flies is closely correlated with adultQuality of Artificially Reared Biocontrol Agents 119