and Integrated Pest Management - part - usaid

DEVELOPMENT OF SIMPLE SAMPLING METHODS
FOR PEST SURVEILLANCE IN RICE
B. Heucl-Rolf and P. Vungsilabutr
Thai-Gcrman Plant Protection Program
P.O. Box 9-100, Bangkok 10900, Thailand
Pest surveillance may serve two purposes, tactical decision-making and/or
strategy development (Heong 1983). This paper deals only with the first aspect
of surveillance, the gathering of information as a sound basis for pest control
decisions.
Under conditions prevailing in rice production in Thailand, this kind of
surveillance information cannot be provided for all rice farmers by governmental
services (-leuel-Rolf & Waibel 1985). The available personnel and budget limit
such activities to selected farmers only. Instead of monitoring the pest situation
in a limited number of fields, the scarce resources of the surveillance service can
be used more effectively for farmer-training on pest surveillance methods.
One basic requirement for such a training program is adequate sampling
methods. Sampling methods must be sufficiently reliable for decision-making
and be cost effective, i.e., require low time expenditure per field, and also be very
simple for farmers to use. For example, no complicated calculations should be
involved in the assessment of the infestation level. In cases where many pests
are involved, identification of damage symptoms is easier than searching for
certain pest stages.
Predetermined levels of accuracy combined with low sampling time
requiremcnts and simple pest assessment can be achieved with the sequential
sampling method. Detailed treatises on the underlying concepts and
mathematical formulas may be found in the papers by Waters (1955) and
Onsager (1975). While sequential sampling plans have been developei for a
variety of crops (Pieters 1978), few are published for rice insect pests (Nishida &
Torii 1970, Shepard ct al. 1986).
The highest savings in sampling time in connection with sequential
sampling are achievable when the plan is based on the binomial distribution.
Instead of counting insects or damaged plant parts, only the presence or absence
of pest cr damage symptom is to be recorded. With this approach, considerable
savings in sampling time have been accomplished in cotton (Pieters & Sterling
1975, Sterling 1975).
Some results of the on-going research program on sequential sampling for
major insect pests of rice in Thailand are presented in this paper.
SAMPLING FOR STEIMBORER
Four stemborer species occur on rice in Thailand, of which the most
important are Scirpophagainecriulasand Chilosuppressalis. They are sampled