Mb. Deramos et al., SAMPLE-SIZE DETERMINATION FOR THE STALK-EYED FLY DIOPSIS-LONGICORNIS MACQUART (DIPTERA, DIOPSIDAE) DAMAGE ON RICE UNDER NATURAL FIELD CONDITIONS, Crop protection, 12(8), 1993, pp. 610-616
Proportions of rice tillers damaged by the stalk-eyed fly (SEF), Diops
is longicornis Macquart, were statistically analysed for nine sampling
periods (rice growth stages) to determine the optimal sample size for
use in damage assessment in the future. The major variation (>90%) in
the proportion of damaged tillers was attributable to differences bet
ween hills, with <10% attributable to differences between stations. Th
e effects of stations, although relatively small, were found to be sta
tistically significant in seven of nine sampling periods. Graphs of co
efficient of variation (yBAR) against the number of stations (t) and n
umber of sample hills (n) showed that using t = 2 to t = 4 and n = 20
to n = 25 would give a precision of <2.0%. Damage levels remained almo
st constant during the nine sampling periods, but variability was obse
rved to be greater at the initial and final sampling periods, and smal
ler in the intermediate sampling periods. The optimal combinations of
the number of stations (t(opt)) and sample size (n(opt)) were obtained
for a given ratio of the cost due to station (C(S)) to the cost due t
o hill (C(H)).