and Integrated Pest Management - part - usaid

W'"
-)l
Z--1
SAMPLING METIODS FOR P.ST SURVILLANCE INRICE 115
STEMBORER
hiuldamogod - I
hillundamaged -0
P 1 0.50 am 0.20 2 - -
P 2 o2a ,- .o 3
4 0-4
20 5 0.5
O7
TREAT 8
o'
.1%
-
6 1 6
9
10
11
12
13
14
1.6
2 7__
3 ­ 7
3-.8
4 - 9
4 - 9
5 -. 10
6-10
15
16
6 -_11
7 -_ 12
NOTREATMENT
17
18
19
7 - 12
8 -13
9 -.13
10 20
NUMBER HILLS SAMPLED
30
(n)
20
21
22
23
9_-.14
10 - 14
10 -15
11 16
Figure 2. Binomial sequential sampling plan for stemborcr in transplanted rice.
Using the formulas given by Onsager (1975), the theoretical maximum
number of sample units to be taken was estimated to be approximately 23.
Thus, at certain infestation levels, the sequential sampling method requires a
higher number of hills to be examined for stemborer damage than the currently
used sampling method of the surveillance service of the Department of
Agricultural Extension (Anon 1985). In the surveillance guidelines, a sample
size of 10 hills is fixed and it is recommended that an additional 10 hills be
examined if a mean close to the economic threshold resulted from the sampling
of the first 10 hills. Therefore, the sequential sampling method can only be
accepted if the reduced time for examination of one hill, as well as the reduced
sample size for low and high infestation levels, result on average in a reduced
sampling time per field.
The sampling plan described above was developed for transplanted rice and
cannot be applied in direct seeded rice because, besides other factors, the sample
unit a.id thcr,, fore also the economic threshold, are different. Preliminary results
on developing a model indicate a linear relationship between mean number of
deadhcearts per sample unit, a cluster of 10 tillers, and the proportion of infested
sample units.
SAMPLING FOR GALL MIDGE
The same approach, as for stemborer, was followed in the development of a
sequential sampling plan for rice gall imidge3 (Or.eolia oryzae). First, a model for