measured the performance ofTrichogramma
in a maze in the laboratory to predict its dis-
persal capacity in the field. Disappointingly,
it appeared that the laboratory bioassay with
the maze did not properly predict dispersal
capacity of Trichogramma in the field. Many
other dispersal tests are in development, but
data obtained in the field are often rare. An
interesting approach for a field-performance
test has been described by van Schelt and
Ravensberg (1990). Their goal was to com-
pare the capacity to control Ostrinia nubilalis
in maize by Trichogramma maidisthat were
either obtained from diapause storage or
freshly reared. In the laboraratory, percent-
age emergence, sex ratio and fecundity were
determined of diapause and freshly reared
parasitoids. Vials with parasitoids of the
same samples as the laboratory material
were put at a central release point in a maize
crop. From the release point, cards with sen-
tinel O. nubilaliseggs were hung on maize
plants in eight directions, with an interval of
1 m and up to 10 m away from the release
point. Percentage parasitism was determined
on these cards. The laboratory results
showed no differences in emergence and
fecundity between the diapause and fresh
parasitoids, but the sex ratio of the diapause
parasitoids was lower than that of fresh
ones. The field tests showed that diapause
and fresh parasitoids dispersed in all direc-
tions, but that percentage parasitism by fresh
parasitoids was higher than that of diapause
parasitoids (van Schelt and Ravensberg,
1990). The results obtained with one of the
flight tests are described below to illustrate
developments in this area.
A short-range flight test has been devel-
oped for Encarsia formosa, i.e. a test where the
parasitoid has to fly a distance of 4–20 cm
(Posthuma-Doodeman et al., 1996). Such dis-
tances are similar to distances between
leaves in a plant. We have experienced that
some methods of producing or storing E. for-
mosacan lead to defective individuals that
are unable to fly even such short distances,
and that was the reason for developing this
test. This short-range flight test is run in a
glass cylinder that has a glass cover with
sticky material on the underside. A barrier of
repellent material (e.g. Blistex lippomade),
4 cm in height, is applied to the vertical wall
of the cylinder to prevents wasps from walk-
ing to the sticky material on the glass cover
plate at the top (Fig. 19.2). Parasitoids are put
on leaves or on cards on the bottom of the
cylinder. The whole set-up consists of stan-
dardized parts, is easy to assemble and
reusable and uses a small amount of space
(400 cm^2 ) per glass cylinder. Counting of the
trapped wasps can be done rapidly (2 min
per cylinder) and without manipulation of
the cylinder. The effects of parasitoid rearing,
handling and storage conditions can be eval-
uated with this test. This test can also be
used for concurrent measurement of imma-
ture mortality and parasitoid emergence pat-
tern, elements that are included in the
current quality control guideline.
The short-range flight test is suitable,
among other things, for evaluating the effect
of storage periods, temperature and handl-
ing procedures on the flight capability of270 J.C. van Lenteren et al.
16 cm20 cmFig. 19.2.Set-up of short-range flight test for
Encarsia formosa.The glass cylinder of 16 cm
diameter and 20 cm high is covered with a glass
plate, which has a circle of glue on the underside.
On the inside wall at the upper part of the cylinder,
a 4 cm high strip of repellent material is applied so
that the parasitoids cannot walk into the glue, but
have to fly. Pupae on leaf or paper are put on the
glass bottom of the cylinder.