and Integrated Pest Management - part - usaid

BIOLOGICAL CONTROL OF CORN STALK BORER IN
THE PHILIPPINES
L. C. Tran-Gruber
GTZ/PGCPP-Biolab, Bureau of Plant Industry
692 San Andrcs Street, Malate, Metro Manila
Philippines
One of the factors limiting corn production in Southeast Asia is the Asian
Corn Stalk Borer Ostrinia furnacalisGuence. The promising effect of
Trichogratnma evanescens Westw. on corn stalk borer in the Philippines in
1983-1984, with 40-76.9% parasitism having been obtained at six locations
(Tran & Hassan 1984) led to further studies on biological control of corn stalk
borer, in particular the performance of 7". evanescens against O.furnacalis.
MATERIALS AND METHODS
7'. evanescens was mass-reared mainly on eggs of Sitotroga cereatellaand
partly on Corcyra cephalonica. The parasitized host eggs were glued on
cardboards (1 x 6 cm) with 1,500-2,000 eggs per card. Trichogramma was
inundatively released at 200,000 parasitoids per release when the first corn stalk
borer eggmasses were found in the ficld. The distance between two release
points was 7-10 in and between plots was 50,-100 m. The number of releases
varied between two and five per cropping season.
Monitoring of parasitism was conducted before the first release and at 7-10
day intervals after the release. The control plot was also monitored for possible
natural parasitism. The dissection of 100 plants per treatment, taken at random
from the two plots for larvae, pupae, and entrance holes of corn stalk borers was
made one week prior to harvest to verify the effect of Trichogramrna.
Concurrently, a survey of Trichogrammnaparasitism was conducted in the
areas where Trichograinmahad been released in previous years to determine the
extent of Trichograltrnaoccurrence in the field(s).
RESULTS AND DISCUSSIONS
In 1983, the lowest parasitism recorded was 40% in the released field (Tran
& Hassan 1984). There was no single parasitized eggmass observed prior to the
introduction of T. evanescens. Table I (Tran et al. 1986) shows the average
parasitism obtained at different locations in the Philippines. The trend of
parasitism was to increase over the years from 1983-1985, and to decrease in
1986. The low parasitism especially in Tacurong (32.2%) could be related to
low corn borer population, which was only 0.6 eggmasses per plant at 51 days
after planting (DAP), and possibly to the poor quality of Trichogrammareleased
(in terms of sex ratio, % parasitism and % emergence).