An effective biological control for corn borer
Corn is one of the most
important staple food in the country, next to rice. But the
corn industry is suffering from tremendous yield loss due to
increasing incidence of diseases and infestation of insect pests,
the most destructive of which is the corn borer which cause a
yield loss of 20-80%.
Nowadays however, corn farmers are able to regulate population
densities of an organism by other organisms. Thanks
to trichogramma evanescens spp. the biological control
agent of corn borer.
The decentralization of the mass production and utilization of
this parasite started as early as 1984. To date, all Regional
Crop Protection Center offices have established their own rearing
Advantages of using trichogramma:
They attack only insects belonging to order lepidoptera, most
member of which are insect pests, unlike when using pesticides,
where pests develop pesticide resistance. Hence there is no problem
of developing pest resistance or resurgence. Rearing of trichogramma
can be done using locally available materials. Field application
and release of the parasite require less labor, with no hazards
to humans and the environment.
Biological control or the use of natural enemies is more effective
and economical than the use of pesticides. It creates a balance
of pests and beneficial species.
Components of successful mass production
1. Most effective species are determined.
2. To maintain parasite quality, rearing procedures include semi-
field conditions and renewal of the colony after six generations.
3. Development of effective release and distribution methods
for field application.
4. Strong relationship between rates of egg parasitism and reduction
in densities of borer larvae, leading to commercially accepted
levels of control.
Poor quality of mass reared Trichogramma
can result in control failures. The artificial conditions of
mass rearing can bring about changes that reduce the effectiveness
of the Trichogramma in the field. Such rearing conditions include
rearing multiple generations on unnatural host eggs, the absence
of plants, crowding and interference, rapid generation time,
and failure to rejuvenate genetic stock.
Methods for Releasing Trichogramma
Trichogramma are typically shipped and released as pupae
inside the host egg. Unhatched trichogramma are glued to trichocards
which are then attached/hung on the third or fourth leaf from
the ground or at about mid-height of the corn plant. Each trichocard
contains about 1,500-2,000 trichogramma. One hectare of corn
plants require 70 pieces of trichocards.
Trichogramma are initially released 4 weeks after planting.
The second release can be done 5 weeks after planting. A distance
of 12 meter or 17 steps between each trichocard is recommended
to distribute the trichocards in the entire field evenly. A
high proportion of females in the released Trichogramma is also
important as only the females parasitize host eggs. The insectary
standard is at least 50 percent females.
For the year 2004, the Regional Biological Control Laboratory
of the Department of Agriculture RFU 5 has distributed a total
of 27,403 trichocards to 13 corn cluster areas and 2 non-corn
cluster areas covering 346.6 hectares benefitting some 182 farmers
in the region.
Evaluating Releases of Trichogramma
Field releases of Trichogramma are evaluated by measuring egg
parasitism, larval densities, crop damage and economic return
relative to similar fields treated with insecticides or not treated.
Egg parasitism measures pest mortality directly and is determined
by collecting eggs from the field. Parasitism is evidenced by
eggs turning black or by the emergence of a wasp.
Trichogramma wasps kill host eggs by feeding on them. The host
egg is stung and the adult feeds on the drop of liquid appearing
at the site of the sting, but no egg is laid. The host egg dies,
leaving no evidence of parasitism.
The densities of larvae must also be assessed because increased
egg parasitism and mortality may not reduce densities of damaging
larvae. For some pests an increase in egg parasitism by Trichogramma
may represent compensatory or replaceable mortality rather than
additive mortality. Comparisons of crop damage, yield and quality
are important in assessing the economic return on augmenting
When evaluating Trichogramma releases it is important to remember
the indirect benefits. Unlike many insecticides, Trichogramma
have very little impact on other natural enemies which may be
valuable in holding the target pest and secondary pests in check.
Also, mass rearing do not pose risks to field workers or leave
toxic residues on produce
Environmental Factors that Affect
The ability of released Trichogramma to locate host eggs
depends in part on the distribution pattern of the Trichogramma
in the field, the release technique, the size and structure of
the crop, and the location of the host eggs. The distribution
pattern should bring Trichogramma as close as possible to host
eggs to reduce searching time by the wasp.
Weather conditions such as low temperatures and rain can
reduce searching and parasitism. Wasps are easily transported
by wind and may be blown out of release fields. In corn, 40 to
60 percent of released Trichogramma daily move out of the field
available at the Regional Crop Protection Center (RCPC) of the
Department of Agriculture RFU 5, San Agustin, Pili, Camarines
Sur. Or you can seek assistance from the Agricultural technician
in your locality.
The Trichogramma Technology by B. A. Zaragoza, T. T. Tormes,
A. P. Mutya and F. D Laysa, Department of Agriculture RFU 5;
The Trichogramma Manual By Allen Knutson, Texas A&M University
of the Department of Agriculture RFU 5
Vol. 14 No. 1
January - March 2005