Research Methods in Toxicology and Insecticide Resistance ...

As discussed in Chapter 3, for experimental precision, each unit or insect
must be a constant. Insect populations need to be collected from the same
location and reared in the same nutrition and environmental regimes. At the
same time, there is a need to provide an adequate supply of test insects for
the bioassays. This chapter will discuss the procedures and techniques used to rear
and prepare standardized test materials.
The insects used are planthoppers but the methods can be easily adapted for use
with any insect species.
Collection of insects
A suitable rice fi eld is identifi ed and its location noted, preferably with the name and
geographic position. About 50 healthy unparasitized adult females or about 100 nymphs
are collected from the study fi elds. Planthopper adults, preferably short-winged, are
collected from the base of the rice plants using an aspirator (by mouth or suction bulb)
and placed into test tubes covered with nylon mesh (Fig. 4.1A). Alternatively, insects
can be collected from the fi eld using a sweep net (Fig. 4.1B).
The collected planthoppers are transferred immediately onto clean potted plants
enclosed with circular or rectangular mylar cages. These plants and cages should be
prepared in the research center before going on the collection trip. Alternatively, collected
insects can be transferred to rearing cages with clean potted plants. In China
and Japan, the collected insects are also kept in test tubes with seedlings and small
boxes with seedlings. Collection cages (Fig. 4.2) are then labeled with the respective
collection dates, location names, and geographic positions.
The insects collected are brought back to the research center and reared in a
greenhouse or insectary maintained with a temperature of 27 + 2 °C and 12 hours of
light.
A B
Fig. 4.1. Collection equipment: (A) a mouth aspirator and test tube covered with nylon mesh;
(B) a sweep net.
Research methods in toxicology and insecticide resistance monitoring of rice planthoppers 45