and Integrated Pest Management - part - usaid

74 PES11CIDE MANAGIEMENI- AND IPM IN SOUTHIAST ASIA
produced from local agricultural by-products in the Philippines and Thailand,
with relatively simple technology (Dharmsthiti et al. 1985, Dulmage 1982,
Padua et al. 1986).
Recent tests at IRRI and BIOTECH to screen 312 Philippine strains of B1
have shown that several strains are more toxic to rice, vegtable, and corn insect
pests than the commercial Bt products. Padua et al. (1986) have demonstrated
that several Philippine Bt strains in their collection arc significantly more toxic
to diamondback moth larvae than the commercial formulations used for its
control in Thailand. Tryon (1986) has shown that many of the Philippine
strains of Bt in the BIOTECIH collection are more toxic to eight important rice
pests, with several of these strains being 10 times more toxic to the rice
leaffolder Cnaphalocrocisinedinalisthan the commercial strain. As a result,
BIOTECH (Philippines) and Mal'idol University (Thailand), with funds from the
WHO, have been developing the tLchnology to locally produce Bi insecticide in
commercial cluantities. In this paper, we will discuss the need for Bt in
Southeast Asia and report some initial results of research (lone in the
Philippines.
NEED FOR Bt IN SOUTlIEAST ASIA
Philippines
RICE The use of high-yielding modern rice varieties ,wlV) and broad-spectrum,
petroleum-based insecticides has not provided acceptable insect pest control for
rice farmers in the Philippines. Both technologies, long considered important
insect pest control weapons, have combined to aggravate the situation. The
"genetic treadmill" and the continuous need for the next improved insect resistant
MV is analogous to the "insecticidal treadmill" and both have proven to be
endemic and expensive, placing the Philippine rice farmer in an economic "nowin"
situation. The Green Revolution in the Philippines, which started with the
development, release, and farmer acceptance of MVs, has increased the average
rice yield from 2.2 t/ha in 1966 to 4.5 t/ha in 1985 in Central Luzon, but has
also led to drastic changes in agronomic practices that have unintentionally
increased insect pest problems (Bull 1982, Cordova et al. 1981, Herdt 1978,
Norton & Conway 1977).
The agronomic practices that have increased insect pest problems on MVs
include planting large areas to a single variety, an increase in the number of rice
crops per farm per year, and increased use of fertilizer. It is common practice in
the Philippines to plant large areas of irrigated lowland to a single MV, thus
providing ideal conditions for insects to develop biotypes to break down plant
resistance. Planting a large area to one MV puts extremely high pressure on
selection for and the subsequent evolution of a new, more virulent insect biotype
within a few generations (Odhiambo 1982). The well-documented evolution of
prolific brown planthopper (Nilaparvatalugens) biotypes in response to mass
release of a series of highly resistant MVs over the last 15 years demonstrates
the evolution of biotypes as a real threat to the stability of any insect-resistant
MV with vertical resistance.