size and laid a characteristic number of eggs
in that host. Larger hosts received more eggs
than smaller hosts. Schmidt and Smith (1985,
1987) confirmed Klomp and Teerink’s (1962,
1967) findings by showing that the wasp
measured a host egg during its initial transit
across the egg. When Klomp and Teerink
(1962) moved their Trichogrammafemale from
the initial host to either a larger or a smaller
host following the wasp’s initial transit across
the first host, the female laid a clutch of eggs
in the second host characteristic of that nor-
mally laid in the host from which she was
moved. Thus, she had measured the host’s
size before she was moved. That there is a
characteristic number of wasps emerging
from an egg of a given host species can be
seen clearly in field data, such as those of
Oatman and Platner (1971, 1978) and their
collaborators (Oatman et al., 1983).
To understand the role of nutrition in rela-
tion to host quality and the quality of the
resulting Trichogrammaoffspring, Barrett and
Schmidt (1991) investigated the amount of
amino acids present in several hosts used by
T. minutumand related them to the amount
of amino acids present in the emerging wasp.
They found that Sitotrogaeggs, which typi-
cally issue a single Trichogrammaoffspring,
contained an average of 2.2 g of total amino
acids and produced a wasp that contained an
average of 1.0 g of amino acids. In contrast,
a Manduca sexta (L.) (Lepidoptera:
Sphingidae) egg contained 94 g of amino
acids on average, after that present in the
chorion had been subtracted. Using the
amino acid content of a Trichogrammaemerg-
ing from an S. cerealellaegg as the minimum
required for producing a wasp, they sug-
gested that 80–90 T. minutumshould be pro-
duced from an M. sextaegg. However, in
their laboratory experiments, Schmidt and
Smith (1987) only obtained ten to 20 T. minu-
tumwasps from an M. sextaegg, depending
on the type of experiment they were conduct-
ing. They found that the number of
Trichogramma eggs allocated to a host
depended on the degree of host exposure –
that is, the amount of the egg’s surface that
was exposed to the wasp during its initial
transit across the host. If the egg touched its
neighbours on all sides, it had less exposed
surface and the wasp encountered the sharp
junction between the host and its adjoining
neighbour sooner than if it was a solitary
host. The wasp thus laid fewer eggs in the
host that touched its neighbours. However,
with the solitary host, the wasp covered more
distance before it encountered the junction
between the round, solitary host and the sub-
strate on which it was laid. The experimental
findings of Schmidt and Smith (1987) with
solitary M. sexta eggs match the results
obtained by Oatman and Platner (1971, 1978)
for this same, normally solitary host during a
3-year field study in southern California
tomato fields. Oatman and Platner (1971,
1978) reported an average of 21.1, 26.7 and
26.3 T. pretiosumper M. sextaegg, respec-
tively, for each of the years in their study.
Thus, the number of eggs a Trichogramma
allocates to this host (20–30 eggs (Oatman
and Platner, 1971, 1978)) is nowhere near the
number that this host can support, i.e. 80–90,
based on the nutritional requirements of a
Trichogrammaemerging from a Sitotrogaegg
(Barrett and Schmidt, 1991).Is bigger better?So why should Trichogrammameasure host
size and regulate the number of eggs it lays
in a host? It has been shown that wasp size,
up to a point, influences a female’s success in
encountering hosts in the field: the larger the
female parasitoid, the more likely she will
encounter a host and, therefore, reproduce
(Fig. 17.1; Kazmer and Luck, 1995; Bennett
and Hoffmann, 1998). Kazmer and Luck
(1995) conducted a set of field experiments to
determine whether the ability of T. pretiosum
females to find hosts in a southern California
tomato field was related to their size. They
estimated the size distribution of searching
females by sampling a host population in a
southern California tomato field. During a
single day, they collected parasitized hosts
by randomly sampling tomato plants in their
experimental plots and collecting from them
the eggs of the cabbage looper, Trichoplusia ni
(Hübner) (Lepidoptera: Noctuidae), the
tomato fruit worm, Helicoverpa(= Heliothis)
zea(Broddie) (Lepidoptera: Noctuidae), andBehavioural Approaches for Quality Control 237