The Asian corn borer, Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae) is an economically important pest of corn. Finding simple, cheap, and suitable rearing techniques of O. furnacalis is an urgent need to support research for management of this insect. This research aimed to determine the suitability of a read bean and rice branbased artificial diet used for mass rearing of this insect since 2009. The tested artificial diet was compared with the natural diet (sweet corn kernel) and each diet was tested in individual rearing method (one larva in each vial). The criteria used to justify the quality of diet and mass rearing procedure were based on the fitness of O. furnacalis. The degree of fitness was based on life history, growth, and development. In general, the fitness parameteres observed from O. furnacalis reared in the artificial diet at 25.7 ± 1.6 °C with 57.7 ± 3.8% RH, and L12:D12 were similar than those in the natural diet. Therefore, the existing artificial diet and rearing procedure were considered suitable and qualified for O.furnacalis. It is important to periodically check the laboratory colony to ensure that they have similar fitness to those found in the natural population.

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Journal of Asia-Pacific Entomology
journal homepage: www.elsevier.com/locate/jape
Fitness of Asian corn borer, Ostrinia furnacalis (Lepidoptera: Crambidae)
reared in an artificial diet
Teguh Rahayu, Y.Andi Trisyono
⁎
, Witjaksono
Department of Crop Protection, Faculty of Agriculture, Universitas Gadjah Mada, Road Flora No.1 Bulaksumur, Yogyakarta 55281, Indonesia
A R T I C L E I N F O
Keywords:
Ostrinia furnacalis
Mass rearing
Artificial diet
Fitness
A B S T R A C T
The Asian corn borer, Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae) is an economically important pest of
corn. Finding simple, cheap, and suitable rearing techniques of O. furnacalis is an urgent need to support research
for management of this insect. This research aimed to determine the suitability of a read bean and rice bran-
based artificial diet used for mass rearing of this insect since 2009.
The tested artificial diet was compared with the natural diet (sweet corn kernel) and each diet was tested in
individual rearing method (one larva in each vial). The criteria used to justify the quality of diet and mass
rearing procedure were based on the fitness of O. furnacalis. The degree of fitness was based on life history,
growth, and development. In general, the fitness parameteres observed from O. furnacalis reared in the artificial
diet at 25.7 ± 1.6 °C with 57.7 ± 3.8% RH, and L12:D12 were similar than those in the natural diet.
Therefore, the existing artificial diet and rearing procedure were considered suitable and qualified for O.
furnacalis. It is important to periodically check the laboratory colony to ensure that they have similar fitness to
those found in the natural population.
Introduction
The Asian corn borer, Ostrinia furnacalis (Guenée) (Lepidoptera:
Crambidae) is an important pest of corn in Indonesia. Beside causing
damage to corn (Zea mays: Graminae), this insect also attacks other
plants from the families of Cucurbitaceae, Malvaceae, Phytolaccaceae,
Poaceae, Polygonaceae, Solanaceae, and Zingiberaceae (Nafus and
Schreiner, 1991; Ishikawa et al., 1999). The larva of O. furnacalis feeds
all parts of the corn plant at all stages of the plant growth (Nafus and
Schreiner, 1987, 1991). When the larvae feed on the vegetative growth
stages of corn, specific damage symptom is shown by parallel small
holes in the shoot whorl. Subiadi et al., (2014) reported that single
larva of O. furnacalis attacking the corn stem during the V10 phase
would lead to yield loss of 4.94%. Furthermore, the number of egg
masses laid per plant could range 7 – 9 (da Lopez et al., 2014; Subiadi
et al., 2014).
Mass rearing is a process to produce a large number of insect using
natural or artificial diet for different purposes, mainly as to study the
biology of beneficial insects, to test insecticides, to produce biological
control agents, to determine economic injury level of particular pests, to
test the effect of Bacillus thuringiensis (Bt) toxins on the non-target pest
(Singh, 1982; Subiadi et al., 2014; Pratiwi et al., 2016), and to provide a
sufficient amount of insects for developing crop resistance to particular
insects through conventional breeding schemes and the use of bio-
technology. Previous research (Resilva et al., 2007; Muralimohan et al.,
2009; Elvira et al., 2010; Pratiwi et al., 2016; Gao et al., 2017; Kim
et al., 2017) reported that the mass rearing of Bactrocera philippinensis,
Pectinophora gossypiella, Spodoptera litura, O. furnacalis, Cnaphalocrocis
medinalis, Drosophila suzukii, either using artificial or natural diet could
be used to improve control techniques for those pests.
A suitable artificial diet is needed in mass rearing to produce uni-
form insects for commercial purposes, such as companies involving in
selling insects for screening insecticides, pheromones, host plant re-
sistance, and for producing biocontrol agents or research (Cohen,
2001). Under certain circumstances, artificial diet often provide more
benefits than natural diet to rear particular insects, for example Spo-
doptera litura, O. furnacalis, Chilo suppressalis (Gupta et al., 2005;
Martaya, 2007; Han et al., 2012), because the natural diet is more la-
borious, messy, needs a large space, and could produce only a limited-
number of insects. Previous study (Ojala et al., 2005; Martaya, 2007)
showed that mass rearing of O. furnacalis using the natural diet required
replacement of the natural diet every one or two days, hence it is in-
efficient. In addition, the fitness of insect reared by artificial diet was as
good as those fed with natural diet (Wang et al., 2013). Therefore, the
increasing demand for a lot of insects necessitates the development of
efficient and economical methods for rearing insects in the laboratory
https://doi.org/10.1016/j.aspen.2018.06.003
Received 11 June 2017; Received in revised form 22 March 2018; Accepted 4 June 2018
⁎
Corresponding author.
E-mail address: anditrisyono@ugm.ac.id (Y.A. Trisyono).
Journal of Asia-Pacific Entomology 21 (2018) 823–828
Available online 08 June 2018
1226-8615/ © 2018 Published by Elsevier B.V. on behalf of Korean Society of Applied Entomology.
T

2. with artificial diets. The goal of large-scale mass rearing is to produce
the maximum number of insects with minimum labor, space, and cost
(Singh, 1982), therefore finding a simple and cheap artificial diet that
produces insect with good fitness is an essential need.
Mass rearing technique of O. nubilalis using artificial diet was first
developed by Bottger (1942). Thirteen years later, the rearing tech-
nique of O. furnacalis was further developed by Kamano and Inoue
using derivated-artificial diet based on Beck (Gahukar, 1976; Hirai and
Legacion, 1985). Song et al. (1999) reported the success of using the
non-agar diet to reduce the preparation procedure steps and the cost of
diet in rearing this insect. Since then, research has been intensified by
availability of artificial diet. For examples in Indonesia, an artificial diet
was used to produce sufficient number of larvae to determine economic
injury levels of O. furnacalis in the three phases of the corn growth in
the field and its susceptibility to toxin Cry1Ac (Ei et al., 2008; Subiadi
et al., 2014).
Martaya (2007) reported that a read bean and rice bran-based ar-
tificial diet was suitable for rearing one generation of the field-collected
O. furnacalis. This artificial diet was originally developed and designed
for Helicoverpa armigera (Budiharjo Sugiyanto, personal communication
in 2001) and modified several times during 2005–2006 (Y.A. Trisyono,
unpublished) before being tested for rearing of O. furnacalis (Martaya,
2007). To establish a laboratory-adapted population of O. furnacalis,
sixty larvae were collected from Sleman, the Special Province of Yo-
gyakarta, Indonesia in 2009. These collected larvae were reared using a
diet and procedure as described in Martaya (2007). After four years of
mass rearing in the laboratory without any additional field collection,
the growth and development of O. furnacalis was determined to justify
the fitness of the colony and the suitability of the diet. This step was
considered very important to produce healthy larvae that would be
used for many different entomological studies. Furthermore, this la-
boratory-adapted colony which had no exposure to any kind of tox-
icants will serve as a reference susceptible population when resistance
studies are carried out.
Materials and methods
Artificial diet preparation
An artificial diet originally for H. armigera (Budiharjo Sugiyanto,
personal communication in 2001) was modified and tested several
times by Y. Andi Trisyono during the period of 2005–2006 (un-
published). After the developed diet was successful for rearing one
generation of O. furnacalis, Martaya (2007) experimentally tested the
developed artificial diet in supporting the growth and development of
this insect. The final modification made by Y. Andi Trisyono in 2006
(Table 1) was reported to be suitable for rearing one generation of O.
furnacalis of a field-collected population from the District of Sleman, the
Special Province of Yogyakarta, Indonesia in 2007. Findings reported
by Martaya (2007) was used as the bases to establish a laboratory-
adapted population of O. furnacalis.
Ostrinia furnacalis colony
The founding population of O. furnacalis (60 larvae) of the labora-
tory-adapted population was collected from the District of Sleman, the
Special Province of Yogyakarta, Indonesia in 2009. Since the collection,
O. furnacalis has been reared using the artificial diet as described above
without any additional field population. The effect of long-term mass
rearing of laboratory-adapted insects to their fitness is an important
consideration when applying research to compare them (as susceptible
population) to wild populations. Previous research showed that there
was no reduction in average body weight, rate of growth, adult long-
evity or fecundity of O. nubilalis reared in the same artificial diet during
8 consecutive generations (Beck et al., 1968; Grayson et al., 2015). In
contrast, changing in photoperiodic responses occured in the labora-
tory-adapted population of Diatraea grandiosella (Takeda and
Chippendale, 1982). Considering these facts, the fitness of O. furnacalis
was determined after being reared for four years in the laboratory using
the artificial diet.
Experimental design
Treatments
This experiment consisted of two treatments: the artificial diet and
the sweet corn kernel (natural diet) as control. We used the kernel of
the cob rather than stalk because the cob provided a faster development
time (Nafus and Schreiner, 1991) and the technique was simpler. Each
diet was tested by employing individual rearing method (one larva/
vial) using plastic vials (4 cm in diameter and 4.7 cm in height). The
experiment was carried out under the regimes of 25.7 ± 1.6 °C with
57.7 ± 3.8% RH (Termohygrometer Haar-Synt.Higro), and L12:D12.
Setting the experiments and fitness observations
The experiments were divided into three different batches to avoid
the physiological stresses of O. furnacalis due to the observations and
handlings.
First batch: weight and head capsule width of newly hatched larvae
The first batch was for measuring weight and head capsule width of
newly emerged larvae. Twenty newly hatched larvae were probed
carefully using a fine hair brush to ensure they were alive and active
and weighed to calculate the average weight of first instars. Weighing
was repeated five times using different larvae. From those twenty
larvae, 16 larvae were taken randomly to measure head capsule width.
Second batch: weight, head capsule width, and developmental time of the
second to the fifth instars
Five to the seven egg masses were put into a jar (14 cm in diameter
and 6.2 cm in height) with a moist-tissue. The newly hatched larvae
were transfered individually into each vial containing a cube of artifi-
cial diet (2 g/larva) or the kernel of the cob (regularly supplied with the
fresh sweet corn kernel daily). Those larvae were reared in vials until
reaching second, third, forth, and fifth instars, pupae, or adults for
observation.
The second batch was intended to determine larval longevity (80
larvae, 16 samples per instar), and larval weight and larval head cap-
sule width (64 larvae, 16 samples per instar). The weight and head
capsule width of second to fifth instar came from the same samples.
Sixteen larvae of first, second, third, and fourth instars which already
molted were used to observe the weight and the head capsule width of
second, third, fourth, and fifth instars, respectively using different
larvae for each instar.
Table 1
The ingredients of the tested artificial diet for mass rearing
of Ostrinia furnacalis.
No. Ingredient Quantity (g)
1 Red bean
2 Agar
3 Rice bran
4 Yeast
5 Sorbic acid
6 Methyl benzoate
7 Tetracycline
8 Vitamin mixturea
9 Casein
130
40
160
62
3
5
0.5
5
3
Source: Y. Andi Trisyono (2006, unpublished).
Note: The diet was prepared in 1000 mL aquadest.
a
Vanderzant Product# F8045 was purchased from Bio-
Serv Entomology Division (www.bio-serv.com/).
T. Rahayu et al. Journal of Asia-Pacific Entomology 21 (2018) 823–828
824

3. Third batch: survival rate, pupal and adult developmental time, and sex ratio
We employed the same design as mentioned in the second batch,
and the only difference was the number of tested insects. Forty eight
larvae were used for the third batch to determine the percentage of
pupation, adult emergence, and the sex ratio (pupae and adults). Pupae
were sexed and determined their weight and longevity individually (16
pupae for each sex), and they were also used to observe adult longevity.
The thirty two pupae collected from the third batch were kept in-
dividually in plastic cups (6 cm in upper diameter, 4.5 cm in lower
diameter, and 4.5 cm in height) until adults emerged. The adults were
fed with honey solution 10% dropped on the tissue. NaOCl (5.25%) was
used to sterilize all equipments for rearing.
One day after larval and pupal molting, larvae and pupae were
weighed individually (Beck, 1950; Gahukar, 1976) with an analytical
balance (Shimadzu AW120). At the same time, their head widths were
measured across the widest section of the head (Becker et al., 2009)
with a stereo-microscope (Leica MZ16, Leica Microsystems [Schweiz]
AG, Heerbrugg, Switzerland).
Data analysis
The criteria used to justify the quality of diet and mass rearing
procedure were based on the fitness of O. furnacalis. The degree of
fitness was based on developmental time (life history of newly hatched
larvae until adults), size of larvae and pupae (larval and pupal weight,
and larval head capsule width), immature survival (larvae and pupae),
adult emergence, and sex ratio of pupae and adults. Data on the de-
velopmental time of larvae to adults were generated from the second
and third batches. Larval and pupal weight, and larval head capsule
width came from first, second, and third batches. Immature survival
(larvae and pupae), adult emergence, and sex ratio (pupae and adults)
came from third batch.
The ratio of the head capsule width was calculated based on Dyar's
Rule (Gullan and Cranston, 2005). Regression and correlation analysis
was carried out to determine the relationship between head capsule
widths (transformed to logarithms) and the instars of O. furnacalis
(Beck, 1950; Gullan and Cranston, 2005). Relationship between larval
weight and head capsule widths was analyzed using the power re-
gression model (Beck, 1950; Becker et al., 2009). Sex ratio (pupae and
adults) was calculated based on Hirai and Legacion (1985) and further
analyzed using Chi-Square Test based on Gomez and Gomez (1984).
Growth and developmental rates of O. furnacalis {Larval Growth Index
[LGI = % Pupation/Larval Period (day)], Pupal Growth Index
[PGI = % Adult Emergence/Pupal Period (day)], Total Developmental
Index [TDI = % Survival/Total Developmental Period (day)], Fitness
Index [FI = (% Pupation x Pupal Weight)/(Larval Period + Pupal
Period)], and Standarized Growth Index [SGI = Pupal Weight/Larval
Period (day)]} were calculated based on Gupta et al. (2005) and Amer
and El-Sayed (2014). The data of developmental time, larval and pupal
weight, larval head capsule width, growth and development rates of O.
furnacalis were analyzed using independent t-test by R-analysis statis-
tical software for Windows 32-bit (standar version 3.1.1 by R Core
Team, www.r-project.org) at the error rate = 0.05.
Results
Developmental time of Ostrinia furnacalis
The longevity of O. furnacalis (larvae to adults) reared using the
artificial and natural diets was similar (t = −0.593, df = 30, P = .558)
(Table 2), although the larval stage was longer in the artificial diet than
that in the natural diet (t = −2.853, df = 30, P = .008). This difference
was due to the second and third instars (t = −3.162, df = 30, P < .01;
t = −3.934, df = 30, P < .01, respectively). Immature developmental
time (longevity of larvae to pupae) was shorter in the natural diet than
that in artificial diet (t = −2.779, df = 30, P = .009). In contrast, the
female took longer time to develop in the natural diet than that in the
artificial diet (t = 4.203, df = 30, P < .01).
The larval and pupal weight of Ostrinia furnacalis
The artificial diet produced heavier larvae, particularly for the third
and fourth instars (t = −2.521, df = 30, P = .017 and t = −2.360,
df = 30, P = .025, respectively) (Table 3). However, the weight of fifth
instar and male pupae was similar (t = −0.153, df = 30, P = .880;
t = 0.202, df = 30, P = .841, respectively). On the other hand, the
weight of female pupae developed from the natural diet was higher
than those from the artificial diet (t = 2.462, df = 30, P = .020). These
results showed that there were no consistent facts that one diet was
better than the other based on the weight.
The head capsule size relative to instars and weight of Ostrinia furnacalis
larvae
The regression and correlation analysis revealed that the two diets
were very similar in terms of head capsule size relative to instars and
weight (Figs. 1 and 2). Those correlation values were closed to 1, thus
there was solidly relationship between instars and the larval head
Table 2
Developmental time of Ostrinia furnacalis reared individually on the artificial
and natural diets (corn kernel).
Stage Period (day)
Artificial diet Corn Kernel
1. Larva
I1 2.94 ± 0.06a 2.88 ± 0.09a
I2 2.75 ± 0.11a 2.25 ± 0.11b
I3 3.19 ± 0.19a 2.31 ± 0.12b
I4 3.50 ± 0.16a 3.56 ± 0.16a
I5 6.56 ± 0.16a 6.50 ± 0.21a
Larval stadia (I1- I5) 18.94 ± 0.36a 17.50 ± 0.35b
2. Pupa
Female 7.25 ± 0.11a 7.25 ± 0.17a
Male 8.06 ± 0.14a 8.25 ± 0.11a
Immature Stadia 26.59 ± 0.32a 25.25 ± 0.36b
3. Adult
Female 3.38 ± 0.26b 5.06 ± 0.31a
Male 4.13 ± 0.36a 4.38 ± 0.36a
Larval to adult stadia 30.34 ± 0.38a 29.97 ± 0.51a
Values (mean ± SE, standard error) followed by same letter for each row were
not significantly different according to independent t-test (P = .05). n = 16
samples. I = instar. (Source: Rahayu, 2014)
Table 3
Weight of Ostrinia furnacalis reared individually on the artificial and natural
diets (corn kernel).
Stage Weight (mg)
n Artificial Diet n Corn Kernel
1. Larva
I1 100 0.07 ± 0.002a 100 0.07 ± 0.002a
I2 16 0.59 ± 0.03a 16 0.46 ± 0.06a
I3 16 3.01 ± 0.19a 16 2.41 ± 0.15b
I4 16 12.83 ± 0.70a 16 10.51 ± 0.70b
I5 16 36.67 ± 1.80a 16 36.27 ± 1.91a
2. Pupa
Female 16 85.03 ± 2.55b 16 96.70 ± 4.00a
Male 16 65.86 ± 1.63a 16 66.28 ± 1.23a
Values (mean ± SE, standard error) followed by same letter for each row were
not significantly different according to independent t-test (P = .05). I = instar.
(Source: Rahayu, 2014)
T. Rahayu et al. Journal of Asia-Pacific Entomology 21 (2018) 823–828
825

4. capsules width, and between the head capsule width and the weight of
O. furnacalis larvae. Interestingly, the head capsule width of fourth
instar was wider in the artificial diet than that in the natural diet
(t = −3.136, df = 30, P < .01) (Fig. 1).
The size increment of the head capsule width of Ostrinia furnacalis larvae
The size increment of the head capsule width of O. furnacalis
(Table 4) was very similar as described before in Fig. 1 on I1-I2
(t = −0.181, df = 30, P = .858), I2-I3 (t = −1.302, df = 30,
P = .203), I3-I4 (t = −0.284, df = 30, P = .778), and I4-I5 (t = 1.303,
df = 30, P = .203), respectively. Therefore, the ratio of head capsule
width of O. furnacalis for the two diets was around 1.41–1.68 and it
could be used for estimating the size increment ratio of the head cap-
sule width in each molting of O. furnacalis.
Immature survival, adult emergence, and sex ratio of Ostrinia furnacalis
The percentage of larvae becoming pupae was higher in the artifi-
cial diet (Table 5). However, the percentage of adult emergence and
larva survival rate to adults was higher in the natural diet. Both diets
produced a trend in which the number of males were higher than fe-
males. Furthermore, the sex ratio (pupae and adults) of O. furnacalis
produced by the two diets were also similar (Table 6).
Growth and development rates of Ostrinia furnacalis
The growth and development rates of O. furnacalis based on the
values of PGI, TDI, and SGI were better in the natural diet than that in
the artificial diet (t = 9.213, df = 30, P < .01; t = 5.839, df = 30,
P < .01; t = 3.754, df = 30, P < .01, respectively) (Table 7). How-
ever, the values of LGI and FI for the two diets were similar
(t = −0.266, df = 30, P = .792; t = 1.199, df = 30, P = .239, respec-
tively).
Discussion
The quality of the diet used in insect mass rearing was justified
based on the fitness of the insect produced. The common criteria used
to justify if the insects have good fitness were fast development, size of
larvae and pupae, number of eggs produced, immature survival (larval
and pupal), and adult emergence (Beck, 1950; Ojala et al., 2005; Han
et al., 2012). Although not all parameters observed in this research
Fig. 1. The relationship between the instar and the head capsule width of larvae
of Ostrinia furnacalis reared in the artificial diet and the fresh corn kernel.
ns = not significantly different; s = significantly different at P = .05 using in-
dependent t-test. Samples = 16 larvae for each observation. (Source: Rahayu,
2014)
Fig. 2. The relationship between the weight and the head capsule width of
larvae of Ostrinia furnacalis reared in the artificial diet and the fresh corn kernel.
Samples = 16 larvae for each observation. (Source: Rahayu, 2014)
Table 4
The increment ratio of the head capsule width of Ostrinia furnacalis reared in-
dividually on the artificial and natural diets (corn kernel).
Instar The size increment ratio of the head capsule width
Artificial diet Corn kernel
I1-I2 1.65 ± 0.02a 1.65 ± 0.03a
I2-I3 1.68 ± 0.04a 1.62 ± 0.04a
I3-I4 1.60 ± 0.03a 1.58 ± 0.04a
I4-I5 1.41 ± 0.03a 1.46 ± 0.03a
Values (mean ± SE, standard error) followed by same letter for each row were
not significantly different according to independent t-test (P = .05). n = 16
samples. I = instar. (Source: Rahayu, 2014)
Table 5
The survival of Ostrinia furnacalis reared individually on the artificial and nat-
ural diets (corn kernel).
Stadia Survival rate (%)
Artificial diet Corn kernel
1. Larvae becoming pupae 100 91.7
2. Pupa
Female 37.5 43.2
Male 62.5 56.8
3. Adult emergence
Female 44.4 43.6
Male 55.6 56.4
4. Larvae becoming adults 75.0 81.3
n = 48 samples. (Source: Rahayu, 2014)
Table 6
The sex ratio of Ostrinia furnacalis produced from larvae reared individually on
the artificial and natural diets (corn kernel).
Stages Sex ratio χ2
d.f. χ2
tab Conclusion
Artificial diet Corn kernel
1. Pupae 0.63 0.57 0.31 1 3.84 ns
2. Adults 0.57 0.56 < 0.01 1 3.84 ns
The sex ratio of pupae and adults were not significantly different (P = .05).
n = 48 samples. (Source: Rahayu, 2014)
T. Rahayu et al. Journal of Asia-Pacific Entomology 21 (2018) 823–828
826

5. showed that O. furnacalis reared in the artificial diet grew and devel-
oped similarly or better than that in the natural diet, most parameters
(63%) had no differences or better in the artifical diet. This may suggest
that the artifical diet may considerably support the growth and the
development of this insect. The fecundity of females produced from the
artificial diet was not measured in this research. However, our previous
research showed that there were no differences in the fecundity of fe-
males produced from larvae feeding on the artificial diet and those on
the natural diet (Martaya, 2007; Ei and Trisyono, 2008). Furthermore,
this artifical diet was succesfully used to produce 54,000 newly hatched
larvae in one day during several weeks in a row for studying the re-
sponse of resistant corn to O. furnacalis (Trisyono, 2014). Despite the
success presented in this study, further improvement of the existing
artificial diet is realized and needed.
Previous research reported that the successive rearing on artificial
or natural diet was proved with shorter developmental time of im-
mature and larger larvae and pupae. The larger body of insects reared
on an adequate diet tended to have greater fitness and higher fecundity
(Ojala et al., 2005; Han et al., 2012; Xiao et al., 2016). In this research,
the longevity of larvae reared in the natural diet was mostly shorter
than that in the artificial diet (Table 2) which could suggest that the
natural diet provided better nutritional requirement. Interestingly, the
third and forth instars developed in the artificial diet were heavier than
those in the natural diet (Table 3), but their last instars of O. furnacalis
reared using the two diets were similar. In addition to that, typically
female adults were heavier than male adults in the artificial and natural
diets and that was similar with previous studies (Gahukar, 1976; Park
and Boo, 1993; Ei and Trisyono, 2008). These data indicate the diffi-
culties in drawing the conclusion based on the weight only. Justifica-
tion of the diet suitability must be based on many other criteria.
There was a strong relationship between instars or larval weight
with larval head capsule widths (Figs. 1 and 2). This finding was con-
sistent with the early research showing that there was a linear re-
lationship between instars and logarithms of larval head capsule
widths, and the determining factor for the head capsule width was
weight (Beck, 1950). Therefore, we used the linear regression and the
power regression to determine relationship between instars and larval
head capsule widths (Fig. 1) and between the larval head capsule
widths and larval weights (Fig. 2), respectively. The two models could
be used to estimate relationship between larval head capsule widths
and their instars, and relationship between the size increment of larval
weight and larval head capsule width, respectively.
Generally, the size increment of insect is measured using the single
dimension (e.g., length or width) of the sclerotized-body parts (Gullan
and Cranston, 2005). Previous researches showed that the ratio of size
increment larval head capsule width in each molt generally is constant
(1.3–1.7) and being a characteristic of a particular insect species (Beck,
1950; Gullan and Cranston, 2005). Our research showed that the size
increment ratio of O. furnacalis's head capsule width ranged 1.4–1.7 and
tends to decrease during insect development. The molting from I2 to I3
on the artificial diet had greater increase than other molts, and these
findings were similar with previous research on different species, O.
nubilalis (Beck, 1950). Furthermore, the larval head capsule widths of
O. furnacalis in this research had similar result with Park and Boo
(1993) and even similar with O. nubilalis reported by Beck (1950) and
Got (1988).
The sex ratio of pupae and adults produced from the larvae fed with
the artificial and natural diets was closed to 1:1 (Table 6), indicating
that the two diets did not affect the sex ratio of O. furnacalis. That result
was similar with previous research by Park and Boo (1993) reported
that sex ratio of the wild population of O. furnacalis closed to 1:1. Si-
milar findings were reported by Amer and El-Sayed (2014) and Devi
and Kaur (2015) on different species (H. armigera or C. auricilius). This
finding suggests that artificial diet supported the larvae to develop into
female and male adults. A poor diet would produce more males than
females (Gahukar, 1976). Based on the value of FI (Tabel 7), the fitness
of O. furnacalis reared in the artificial diet was as good as that in the
natural diet. Furthermore, previous studies on S. litura or H. armigera
showed that the growth and development rates of those insect reared in
artificial diet were higher than those fed with natural diet (Gupta et al.,
2005; Amer and El-Sayed, 2014).
The suitability of rearing condition, other than the diet, is crucial for
the diet researcher for rearing the target species. Singh (1982) reported
that temperature around 26 °C and relative humidity of 55–65% was
well for rearing most insect species. In this experiment, temperature
and relative humidity for rearing of O. furnacalis were 25.7 ± 1.6 °C
and 57.7 ± 3.8%, respectively and similar with previous research
(Hung et al., 1988; Park and Boo, 1993; Huang et al., 1998; Xiao et al.,
2016). Therefore, the artificial diet, rearing condition, and rearing
procedures described in the paper could be used continuously to rear O.
furnacalis with understanding that further improvements are necessary,
such as to shorten the larval developmental time and increase the fe-
male weight.
Conclusion
The artificial diet used in our laboratory could be deployed for mass
rearing of O. furnacalis to produce uniform insects in large number.
Moreover, in-depth studies to improve the existing diet and to evaluate
the response of larvae under field conditions become crucial to ensure
that insects produced from this artificial diet maintain the field per-
formance similar to natural populations.
Acknowledgements
The authors would like to thank Sriyanto Haryanto for his support
in artificial diet preparation and providing the egg masses for the
tested-insects; Nugroho Susetya Putra, Suputa and Edhi Martono for
discussion; Noviany and Roi Yanuar Misgi Manullang for assistance in
data analysis; Bram Dortmans and Sharon North for providing language
help in early draft. This research did not receive any specific grant from
funding agencies in the public, commercial, or non-for-profit sectors.
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