Authored by Lucas S Barros
Among the largest fibers and grains cash crop, Brazil is one of
the largest commodity agricultural producer in the world. However,
the insect’s pest intense attack has limited the Brazilian agricultural
crops productivity and sustainability of the main as soybean, corn
and cotton [1].
After genetically modified crops expressing insecticidal proteins
from Bacillus thuringiensis bacterium (Bt) market released as
Integrated Pest Management (IPM) tool, especially for Lepidoptera
order pest control, most of growers believed that losses by insect
pests damage would be minimized.
In fact, Bt has been effective to a target pest group, however
the Insect Resistance Management to Bt plants (IRM) has not been
implemented and resistance cases came out and technologies
failures have been recorded [2,3].
The main IRM strategy have been adopted are Bt plants
expressing high dose protein insecticide associated with refuge
areas (non- Bt plants). However, in most crops field pest resistance
cases to Bt were connection to low refuge areas adoption [4]. Thus,
to ensure field efficacy Bt crops requires growing the refuge area
and pest management insights [5].
Refuge areas represent a part of the grower’s field area
where have to be seeded with non- Bt crop with same agronomic
characteristics of Bt main crop such height and cycle duration. The
function of the refuge area is providing susceptible individuals
(moths) that may mate with rare resistant insects fromBt crop
area. This strategy (high dose and refuge) aims to ensure the
susceptibility to target pests of Bt crop and keep the Bt crops
efficacy [6].
Seed refuge areas can be done in different layout, such as tracks
and borders. In Brazil, it is recommended seed 20% of soybean
and cotton area with non- Bt plants, and 10% corn. Besides that,
the 800 meters maximum distance between Bt and non Bt areas
(structured refuge) is mandatory also [5].
The pest management in refuge areas should be implemented
in accordance with the IPM principles, as samplings and monitoring
target and non-target pests of Bt crops, natural enemies, and
economic threshold (ET) use when necessary for each pest and
crop control decision [2].
The fall armyworm, Spodoptera frugiperda is the main target
pest of Btcorn crop in Brazil. For monitoring this pest in refuge
areas, are needed to visually evaluate 5 different plants in 20
representative point in the area. For control decision, it is applied
a visual defoliation scale Davis from zero to nine (0-9). In this case,
the ET are 20% of plants with equal note or higher than 3 [2,5].
In soybean, monitoring and sampling occur by tapping cloth (1.0
x 1.5 meter) and ET adopted in vegetative stage are 10 Spodoptera
spp. larvae complex (S. eridania, S.cosmioides and S. frugiperda) for
each meter, 4 Heliothinae larvae group (Chloridea virescens and
Helicoverpa spp.) for each meter or 30% of defoliation [2,5].
In reproductive stage, it is recommended to take action when
account 10 Spodoptera spp. larvae complex for each meter, 2
Heliothinae larvae group for each meter, or 15% of defoliation and
10 % attacked pods. Regarding the Anticarsia gemmatalis larvae,
Chrysodeixis includens, Rachiplusia nu and Trichoplusia ni (Plusiinae
complex), the ET are 30% of defoliation or 20 larvae for each meter
in the vegetative stage and 15% defoliation or 20 larvae for each
meter in reproductive stage [2,5].
Unlike these, in cotton crop it is recommended control
measures adoption when detect 15% of plant pointers attacked
with two C. virescens larvae for each plant. For Alabama argilacea,S. eridania and S. cosmioides, the ET adopted is 10% defoliation or 2
larvae for each meter until 40 days after plant emergence. After this
period, the ET is the same of above cited more 25% plant pointers
defoliation [2].
In terms of C. includens in cotton crop, up to 40 days after
emergence, the ET are 10% defoliation or 2 larvae for each meter
and 10% defoliation of plants or 2 larvae for each plant up to this
period. Control decision to C. virescens and Helicoverpa spp. larves
should be done when 6 to 8% of infested plants with at least one
larvae or 5 to 8 larvae in 100 sampled plants.
For S. frugiperda, the ET is 6 to 8% of infested plants with
at least one larve, and for Pectinophora gossypiella larvae ET
recommendations are to 10 adults caught by pheromone trap in at
least 2 nights or until 3 to 5% attacked squares [2].
Faced the potential lepidopteran pests’ infestation and injury
by target and non-target pest on Bt crops in refuge areas, the main
tool used for the management of these pests has currently been
insecticide spray, which should be minimal and when necessary
according ET. Insecticides with low toxicity or selective to natural
enemies, increases growers’ ecological benefits, especially because
these benefit insects are mainly responsible for field pest natural
mortality [5,7].
An example of this scenario occurs with the egg parasitoids
Trichogramma spp. and Telenomus spp., the egg and larvae predators
Doru luteipes and Podisus nigrispinus that are not lethaly affected by
Diamides and Benzoylureas synthetic insecticides chemical group,
as well as microbial Baculovirus insecticide [5,7].
Even though Bacillus thuringiensis (Bt) microbiological
insecticide be lepidopterant-pest effective, this kind of pesticide
should not be spray in refuge areas in order to not affect IRM
strategy [2].
It is important to know that, because there are non- Btt plants
in growers refuge area, target and non-target Bt crop pests may be
more intense plant attack. Particularly in tropical countries such
Brazil where there is intense crop system season, the IPM and IRM
in this scenario has been challenge because polyphagous pests
crop like fall armyworm Spodoptera frugiperda, cotton bollworm
Helicoverpa armigera and soybean looper Chrysodeixis includens
are common and constant attack to Bt crops and non Bt crop [2].
In general, for the growers keep BBt crop technology benefits of
for long periods, the seed and correct pest management of refuge
is mandatory and the decisions to control the target pests should
always be the IPM.
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