Field Guide of Discovery-based Exercises for - Aseanipm ...

Section 4 • Integrated Insect and Rodent Pests Management
Exercise No. 4.15 159
ENHANCING NATURAL ENEMY POPULATIONS BY
USING BACILLUS THURINGIENSIS AGAINST
LEPIDOPTEROUS PESTS OF ORGANICALLY-GROWN
VEGETABLES
BaCKGroUND aND raTIoNalE
Bacillus thuringiensis or Bt is already widely used in
the control of lepidopterous larvae in organically-grown
vegetables in the Philippines. As a microbial insecticide 160 ,
Bt protein is usually used in formulations containing spores
and crystalline inclusions that are released upon metabolism
of Bt during its growth. B. thuringiensis is a gram-positive
bacterium naturally occurring in soil. It kills larvae by
disrupting the digestive system leading to slow growth and
ultimately death. When dose is high, sudden death can usually occur. Bt-based pesticides are
marketed under various trade names. Because of its specificity, it is being used as a complementary
control strategy to Diadegma parasitoid against diamondback moth (DBM) and other lepidopterous
larvae.
In the Cordilleras, Diadegma is used as an egg parasitoid. In cases where eggs escaped and
developed into larvae, Bt is used as a follow-up treatment to specifically kill pest larvae but not
Diadegma. Bt has been found very effective against intended pests but not harmful to their natural
enemies. Despite these positive features, use of Bt-based pesticides also has their own limitation.
They are expensive. It requires several applications as sunlight breaks down toxin and rain removes
active ingredient from plant.
However, many organic vegetable farmers, through years of experience, had evolved some practical
approaches for effectively using Bt to control pests and enhancing natural enemy populations as well.
These experiences must be shared among farmers in FFSs to further improve current approaches in
enhancing natural enemy populations. This exercise was designed to attain this particular objective.
159 Adapted from Callo, Jr., D.P., L.B. Teofilo, and H.A. Tauli (eds). 2002. Field Guide of Discovery-based Exercises for Vegetable IPM, Volume II. SEAMEO
Regional Center for Graduate Study and Research in Agriculture (SEARCA), Los Baños, Laguna, Philippines. pp208-211.
160 IIBC. 1990. Manual on Biological Control and Biological Methods for Insect Pests in the Tropics. FAO/IRRI/IIBC Training Course on Biological Control
in Rice-based Cropping Systems, International Institute of Biological Control, Kuala Lumpur, Malaysia. pp2.3/1-3.2/4 (Part 1), pp1.3/2-1.3/10 (Part 2)
and pp2.6/1-2.6/8 (Part 3).
237
when is this exercise most
appropriate?
ɶ In FFS, TOT, and VST
sessions, when there is
a relatively moderate to
serious lepidopterous pest
infestation on organicallygrown
vegetables in
learning field; and
ɶ When farmers want to
learn the appropriate
time to spray Bt to control
lepidopterous pests
of organically-grown
vegetables.