and Integrated Pest Management - part - usaid

76 PIB'IICIDI."MANAGEMINI'ANI) II1M INSOU'I]lFAST ASIA
and improved irrigation and drainage systcms. Insect problems will also become
more complex as farmers in the Northeast shift from a rice monoculture to new
cropping patterns. Serious yield losses from insect damage have been reported
on sesamc, peanuts, corn, mung bean, and kenaf. Present insecticide alternatives
are unacccptable to the Northeast farmer because they are expensive and toxic to
fish.
INITIAL RESEARCH
Laboratory Screening
Efforts have been underway (Table I) for over a year to screen 295
Philippine Bt strains against the nine major rice pests including Cnaphalocrocis
inedinalis(leaffolder), Alarasiniapatnalis (leaffolder), Chilo suppressalis(stem
borer), Mythimna separata(armyworm), Rivula atimeta (green hairy ca!erpillar),
Narangaaen'scens (green semilooper), Nymphula depunctalis (casewon), and
llydrellia philippina(whorl maggot). Many of these Bt strains (25% average)
are toxic to these insect pests with several significantly more toxic than the
commercial Bt formulations. The most toxic formulation will ultimatcly be the
least expensive to mass-produce. Eventually all Bt strains will need to be
cataloged by toxicity (LC50 ) to specific insect pests and stored for future
reference" and/or use.
On-Farn Trials
WET SEASON 1986 Data obtained from five on-farm trials demonstrated
that plots receiving weekly applications of Bt insecticide had significantly (P <
0.01) larger yields ranging from a low of ±32% to a high of ±192% with an
average increase of ±65% and an average yield of 5.94 t/ha rclative to the
insecticide-free or untreated plots with an average yield of 3.55 t/ha. The rice
yield from the plots receiving weekly applications of Bt were also significantly
(P < 0.01) larger by 29% than the yield from a plot with a similar weekly
application of Bt and two additional applications of monocrotophos at 5 and 12
Table 1. Screening of indigenous isolates of Bacillus thuringiensisfor toxicity
to lepidopterous pests of rice. IRRI, 1986.
Insect pests Isolates
Screened (no.) Toxic (%)
Green semi-looper
Green hairy caterpillar
Leaffolder
Caseworm
Striped stem borer
Yellow stem borer
287
285
276
265
181
55
34
53
26
27
3
13