Bt Research 2015, Vol.6, No.5, 1-10
5
flavicincta
(Figure 4B), treatment T4 (
Bt kurstaki
and
C. flavicincta
) caused 48.8% mortality of
S. frugiperda
and was found to be significantly more efficient compared
with either treatment with
Bt kurstaki
strain HD1
(33.3%) or exposure to
C. flavicincta
parasitism, where
the average mortality was 42.2% (F= 11,3, df= 3,8, p=
0.003).
1.3 Biology of
C. flavicincta
descendants emerging
from
Spodoptera frugiperda
that were exposed or
not exposed to the monogenic
strain
Bt thuringiensis
4412
Data on the biology of
C. flavicincta
were evaluated
through the analysis of parasitoid off spring from
couples that emerged from larvae that were infected or
non-infected by
Bt thuringiensis
4412. The development
period for each phase of
C. flavicincta
is show in Table 1.
The parasitoids obtained from infected or non-infected
larvae showed significantly different average egg-larvae
durations, of 11.1 and 9.9 days, respectively (t = 5.6,
df = 36.9, p <0.05). Regarding the pupal period, the
parasitoids that emerged from the infected larvae
exhibited an average pupal period of 8.9 days, versus
8.5 days for those obtained from uninfected larvae (t=
1.48, df = 16.8, p> 0.05).
The average longevity of the adults that emerged from
infected or uninfected larvae was 15.3 days versus
16.4 days, respectively (t = 5.6, df = 17.3, p> 0.05).
The sex ratios of the parasitoids that emerged from
couples obtained from infected (n = 61) and
uninfected (n = 111) larvae were 1 ♀: 5.1 ♂ and 1 ♀:
♂ 12.75, respectively. The egg-larva and pupal periods
and the longevity of adult insects were also evaluated,
which ranged from 7-25 days and peaked at 14 days
(Figure 5), when the parasitoids that emerged from
infected (n = 61) and non-infected (n = 111) larvae
showed percentages of 22.9 and 15.3%, respectively.
2 Discussion
Studying potential impacts of insect-resistant genetically-
engineered plants on beneficial non-target arthropods
is an important component of the environmental risk
assessment. Our findings demonstrated that the T4
treatment (exposure to both Cry proteins and
C.
flavicincta
) was more effective in controlling
S. frugiperda
compared with the treatments that assessed either only
Table 1 Average duration of the developmental stages (days) of
C. flavicincta
from pairs obtained from
S. frugiperda
larvae that were
either
infected or non-infected by
B. thuringiensis
4412
Infected
Non-Infected
Development Stage
Mean ±Standard Error
Individuals (n)
Mean ±Standard Error
Individuals (n)
Egg-larva
11.1 ±0.16
163
9.9 ±0.11
208
Pupa
8.9 ±0.22
61
8.5 ±0.15
106
Longevity
15.3 ±0.52
61
164 ±0.46
106
Figure 5 Percentage distribution of
Campoletis flavicincta
individuals between different life cycle periods and descendants of couples
from
Spodoptera frugiperda
thatwere either infected or non-infected with
Bacillus thuringiensis
4412. (a) egg-larva phase, (b) pupal
phase
