and Integrated Pest Management - part - usaid

118 PFSTICIDE MANAGEMENT AND IPM IN SOUTIIEAST ASIA
comparison to the presently useCd surveillance method (Anon 1985). The
accuracy of control decisions is improved while the time cxpenditurc for
sampling is reducel.
SAMILING FOR BROWN PLANTI1OPPER
At present, brown l)lan thopper (Nih~lrvat lugens) population densities
have to be assessed by direct counting (Anon 1985). Depending on the
inestation level, ltits can be a very laborious and tile-consuming undertaking.
Therefore, a saripling method basced on the frequency of infestation, i.e.,
presence or absence of hoppers in the sample unit, wouldi mean a significant
improvelflent of the surveillance system.
I lowever, our field data indicated that [lie present sample unit of 10 tillers
seems to be in.suilcd Ifor such a method. As is evident fromt Figure 5, tile
f'requency of int'estalion increase s \'ery rapidly with increasing hopper density.
Thus, at population (lensitiCs below the economic threshold, all sample units
were already infestcd, with at least one hopper lottnd on all of ielm.
There are two Ieasible solutions in order to realize a presence-absence
salplingimethod. First, a smallcr sample unit could be introduced. However,
the 10-tiller sample unit is already well-c.siablislied through the surveillance
scrvic, and one .Jhould try as mitch as possible to retain a standard sample unit
for ;ill insect pests as well is diseaSes.
Lno
00
o 0
z0 0 0 O0 0
-.
1
-1
0
0
00
Ln 0
a .600
U6
w 00
.4 0oo ET=IOBPH/SAMPLE UNIT
0 z 08
.2
CL
1 2 3 4 5 6
MEAN NUMBER BPH/SAMPLE UNIT
Figure 5. The relationship between the proportion of infested sample units and
the mean number of brown plantloppei per sample unit (= 10 tillers).
0