www.elsevier.com/locate/ibmb
Biological activity of two juvenoids and two ecdysteroids against
three stored product insects
Moshe Kostyukovsky
a,*, Bin Chen
b, Shulamith Atsmi
a, Eli Shaaya
aaDepartment of Stored Products, ARO, The Volcani Center, Bet Dagan 50250, Israel bDepartment of Plant Protection, Southwest Agricultural University, Chonqing 400716, China
Received 31 October 1999; received in revised form 31 December 1999; accepted 25 January 2000
Abstract
The insecticidal activity of juvenile hormone agonists methoprene and pyriproxyfen, and the ecdysone agonists RH-5849 and tebufenozide was evaluated against susceptible and actellic-resistant strains of Tribolium castaneum and susceptible strains of
Rhyzo-pertha dominica and Sitophilus oryzae. Concentrations ranging from 0.1 to 20 ppm of the analogues were mixed in the food medium
to which the tested insects were exposed. The results showed that all these compounds could affect the development of the tested species to differing extents but had no effect on the mortality of parental adults. The two JH analogues did not prolong the life span of R. dominica and S. oryzae, but very greatly extended that of T. castaneum. The extension led to the production of giant larvae and failure to pupate. Actellic-resistant strain of T. castaneum showed some cross-resistance to methoprene and pyriproxyfen, but not to RH-5849 and tebufenozide. Pyriproxyfen was the most effective compound among the four IGRs; a concentration of 0.1 ppm could completely inhibit the F1adult occurrence of both S- and R-strains of T. castaneum and its LC90s for controlling
R. dominica and S. oryzae were 0.1 and 1.2 ppm, respectively. Methoprene was highly effective against R. dominica, but less active
on S. oryzae. RH-5849 could achieve almost complete control of F1adults of T. castaneum and R. dominica at 10 ppm, but was
less potent on S. oryzae. Tebufenozide appeared to be much less active on these three species compared with the other three compounds. The percentage reductions of F1adults for S- and R-strains of T. castaneum at a concentration of 20 ppm were 80
and 99%, respectively.2000 Elsevier Science Ltd. All rights reserved.
Keywords: Juvenile hormone; Ecdysone agonist; Methoprene; Pyriproxyfen; RH-5849; Tebufenozide; Tribolium castaneum; Rhyzopertha dominica; Sitophilus oryzae
1. Introduction
The use of fumigants and conventional organic insec-ticides to control insect pests of stored products has given rise to problems of residual toxicity and develop-ment of resistant strains of insects. These problems have enhanced the need to develop more effective and rela-tively safer insecticides (Smet et al., 1990). Insect growth regulators (IGRs) can degrade rapidly in the environment (Staal, 1975; Zurfleuh, 1976) and generally have low mammalian toxicity to non-target species (Staal, 1975; Oberlander et al. 1978, 1997). They are effective against some strains which are resistant to
con-* Corresponding author. Tel.:+972-3-968-35-84; fax:+ 972-3-960-44-28.
E-mail address: [email protected] (M. Kostyukovsky).
0965-1748/00/$ - see front matter2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 5 - 1 7 4 8 ( 0 0 ) 0 0 0 6 3 - 1
ventional insecticides (Amos et al., 1974; Silhacek et al., 1976). Some IGRs have a very high biological activity (Slama et al., 1971, 1974) and could potentially be inte-grated in other insect pest management techniques (IPM) such as biological control (Wright and Spades, 1972). Many studies have demonstrated the effects of a variety of IGRs on various stored product insects (Thomas and Bhatnagar-Thomas, 1968; Silhacek and Oberlander, 1975; Loschiavo, 1976; Nickle, 1979). All of these characteristics make them potentially successful alterna-tives to standard pesticides for insect pest control.
IGRs include compounds that may affect molting and metamorphosis by mimicking juvenile hormone (JH, juvenile hormone agonists) or antagonizing JH activity (ecdysteroid agonists) or by interfering with cuticle for-mation (chitin synthesis inhibitors) (Smet et al., 1990; Oberlander et al., 1997).
Rhyzoper-tha dominica (Fabricius) and Sitophilus oryzae
(Linnaeus) are all economically important pests of stored products, which feed on a wide range of commodities (Arbogast, 1991). Repeated pesticide treatments have led to the increasing incidence of resistance and consequent serious control problems of these species in certain cases (Subramanyam and Hagstrum, 1996). The objective of this study was to compare the efficacy of the juvenile hormone agonist methoprene which is in use as control agent against insect pests of stored products, to the juv-enile hormone agonist pyriproxyfen, and two ecdysteroid agonists, RH-5849 and tebufenozide.
2. Materials and methods
2.1. Insects
The test insect strains were reared in the laboratory over 10 years without any contact with insecticides.
Sito-philus oryzae and Rhyzopertha dominica were reared on
whole soft wheat, and Tribolium castaneum was reared on wheat flour. The actellic-resistant strain of T.
cas-taneum was obtained by raising the laboratory strain on
a culture medium with gradually increasing concen-trations up to 4.5 ppm of the organophosphorus insecti-cide, actellic 50% e.c. (pirimiphos-methyl), for around 20 generations. The insects in the last five generations were raised on 4.5 ppm of actellic without increasing the concentration. All these insects were maintained in 1 l glass jars with paper covers and bred at 27±0.5°C, 70±5% r.h. and light:dark cycle of 8:16 h.
2.2. Insecticides
Four compounds were used in our experiments: Methoprene, [1,isopropyl(2E,4E)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate], supplied by Zoecon Cor-poration, California, USA. Pyriproxyfen, 2-[1-methyl-2-(4-phenoxy-phenoxy)ethoxy]pyridine, supplied by Sum-itomo Chemical Corporation, Ltd., Japan. RH-5849: dibenzoyl hydrazines, (1,2-dibenzoy,1-tert-butyl hydrazine), and Tebufenozide, 3,5-dimethylbenzoic acid 1-(1,1-dimethylethyl)-2-(4-ethylbenzoyl)hydrazide, both supplied by Rohm and Haas Corporation, Spring House, PA, USA.
2.3. Treatments
Stock solutions of the tested IGRs in acetone were prepared at a concentration of 5 mg/ml. Appropriate amounts of the compounds to be tested were dissolved in 10 ml acetone/100 g medium and were thoroughly mixed with the food of each of the target insects. Food treated with acetone alone was used as a control. Care was taken that all acetone had evaporated from the
treated and control samples, by mixing and ventilating the culture medium for 24 h, before insects were added to all treated food. For each treatment 20 adults aged 14–18 days after emergence from the pupae, to allow mating, when used. The insects were placed in a 100 ml jar with 20 g of wheat flour (T. castaneum) or whole wheat (R. dominica and S. oryzae). All insects were kept at 25±0.5°C and 70±5% r.h. at a 8:16 h light:dark cycle. After a period of 15 days during which the insects were allowed to oviposit eggs, the parental adults were removed and their mortality was recorded. The emerged F1 adults were counted twice a week and removed until
emergence was complete. The developmental course and external morphology of larvae, pupae and adults of T.
castaneum were observed. In the cases of R. dominica
and S. oryzae, only live adults found externally were recorded, since the larvae and pupae develop inside the grain kernels. The standard error of the life span means and numbers of F1 adults were calculated. Significance
of differences was analyzed using ANOVA test (P,0.05). The LC50and LC90were calculated according
to POLO-PC probit analysis (LeOra Software, 1987).
3. Results
3.1. Tribolium castaneum
The external morphology, mortality in the various developmental stages, life span, numbers and percentage reduction of F1 adults of susceptible (S) and
actellic-resistant (R) strains of T. castaneum are given in Table 1 and Table 2. The maximum recorded mortality of par-ental adults among all treatments and the control was 5% (not shown). The results showed that methoprene at concentrations of 0.1 ppm and higher wholly prevented the development of F1S-strain adults: most larvae were
abnormal and died in the larval stage except for a small number which died during pupation. As the concen-tration increased, the life span lengthened from 105 days at 0.1 ppm to 139 days at 3 ppm, while that of control was only 67 days. These data were obtained from obser-vation extending from the introduction of F0 adults to
the appearance of all F1adults or 95% mortality of larvae
and pupae. The R-strain was less sensitive to methop-rene: only at a concentration of 3 ppm was a 100% reduction of F1adults obtained. Insect mortality occurred
Table 1
The biological activity of JH agonists Methoprene and Pyriproxifen on development of F1adults of susceptible (S) and actellic-resistant (R) strains
of Tribolium castaneuma
External Stage of abnormal Life span No of adults % reduction of
IGRs Strain Conc. (ppm)
morphology* death (days)(±S.E.M.)bF
1(±S.E.M.)c F1d
Methoprene S 3 L larva 139(4.3)l 0 100
1 L larva 117(5.4)h 0 100
larva, pupation
0.5 lL 105(3.6)g 0 100
(few) larva, pupation
0.1 lL 105(5.4)g 0 100
(few)
R 3 lpP pupa, emergence 82(2.9)f 0 100
1 lpaA emergence, adult 82(3.2)f 13.0(0.4)l 81.9
0.5 lpaA adult (few) 82(2.5)f 56.7(1.3)h 21.2
0.1 lpaA none 82(3.3)f 109(6.8)f 251.4
Pyriproxyfen S 2 L larva 158(6.4)g 0 100
1 L larva 158(7.5)g 0 100
0.5 L larva 158(5.7)g 0 100
0.1 L larva 158(6.2)g 0 100
R 2 L larva 300(7.9)k 0 100
1 L larva 300(10.2)k 0 100
0.5 L larva 300(9.8)k 0 100
0.1 L larva 300(12.3)k 0 100
Control S 0 lpa none 67(2.3)e 69.3(0.8)e 0
R 0 lpa none 67(3.5)e 72.0(0.8)e 0
aThe data are the average of three experiments, each with three replicates. *l,L=larvae; p,P=pupae; a,A=adults; l,p and a=morphology completely
normal; L,P and A=abnormal.bFrom the introduction of F
0adults to the occurrence of all F1adults or death of 95% larvae or pupae.cNumber of
normal adults obtained at the end of F1generation period.dIn comparison with control.e–pDifferent letters indicate statistically significant difference
of averages in the same column with 95% confidence.
Table 2
The biological activity of ecdysone agonists RH-5849 and Tebufenozide on development of F1adults of susceptible (S) and actellic-resistant (R)
strains of Tribolium castaneuma
External Stage of abnormal Life span No. of adults % reduction of
IGRs Strain Conc. (ppm)
morphology* death (days)(±S.E.M.)bF1(±S.E.M.)c F 1d
RH-5849 S 10 lpPa pupa 78(5.9)f 5.3(0.4)n 92.4
7.5 lpPa pupa 78(6.4)f 9.3(0.4)m 86.6
5 lpa pupation 63(4.9)e 37.3(0.9)j 46.2
2.5 lpa pupation 63(3.7)e 47.3(1.5)I 31.7
R 10 lpa pupation 78(6.7)f 2.0(0.8)o 97.2
pupation, adult
7.5 lpa 78(6.1)f 6.3(0.9)n 91.2
(few)
Tebufenozide S 20 lpPa pupa 78(7.8)f 14.0(0.8)l 79.8
15 lpPa pupa 78(7.4)f 21.7(1.2)k 68.7
10 lpa pupation 63(5.4)e 56.7(1.3)h 18.2
R 20 lpaA pupation, adult 78(8.4)f 0.7(0.4)p 99.0
15 lpaA pupation, adult 78(6.7)f 6.0(0.4)n 91.7
Control S 0 lpa none 67(2.3)e 69.3(0.8)e 0
R 0 lpa none 67(3.5)e 72.0(0.8)e 0
aThe data are the average of three experiments, each with three replicates. *l,L=larvae; p,P=pupae; a,A=adults; 1,p and a=morphology completely
normal; L,P and A=abnormal.bFrom the introduction of F
0adults to the occurrence of all F1adults or death of 95% larvae or pupae.cNumber of
normal adults obtained at the end of F1generation period.dIn comparison with control.e–pDifferent letters indicate statistically significant difference
of averages in the same column with 95% confidence.
produced giant larvae with a darker color than those of the control, possibly, as a result of their longer life span. The ecdysone agonists, RH-5849 and tebufenozide, showed relatively lower toxicity to T. castaneum (Table 2) compared with JH agonists. RH-5849 at
concen-trations of 2.5, 5, 7.5 and 10 ppm reduced the F1S-strain
In contrast to their responses to the JH agonist metho-prene, both R and S-strains of Tribolium were suscep-tible to the ecdysone agonist RH-5849: concentrations of 7.5 and 10 ppm of RH-5849 achieved 91 and 97% reduction of F1 adults, respectively (Table 2).
The toxicity of tebufenozide was far lower than that of RH-5849. Exposure of the S-strain to 5, 10, 15 and 20 ppm of tebufenozide caused reduction in F1adults of
only 12, 18, 69 and 80%, respectively. The R-strain was relatively more susceptible than the S-strain, and 92 and 99% control of F1 was obtained at 15 and 20 ppm,
respectively.
3.2. Rhyzopertha dominica
Table 3 shows the numbers and the control percent-ages of F1 adults of a susceptible laboratory strain of R.
dominica, and the LC50and LC90of the four IGRs. The
maximum mortality of parental adults among all treat-ments and the control was 7%. The life span of the F1
generation for all treatments including control was about 62 days, which suggests that the four IGRs had no effect on the life span of this species. Methoprene and pyrip-roxyfen showed high toxicity to R. dominica: at a con-centration of 0.1 ppm, a reduction of 99% of F1 adults
was obtained. The concentration of either juvenoids, methoprene or pyriproxyfen, required for 50 or 90% F1
adult reduction compared with control was less than 0.1 ppm. RH-5849 was less effective: 10 ppm caused 97% reduction of F1 adults, and LC50 and LC90 were 2 and
5 ppm, respectively. Tebufenozide was found to be least
Table 3
The biological activity of various IGRs on development of F1 adults of susceptible laboratory strain of Rhyzopertha dominicaa
IGRs Concentration No. of adults Reduction of F1adults
(ppm) F1(±S.E.M.)* %b LC50(ppm)c LC90(ppm)c Slope (±S.E.M.)
Methoprene 3 0o 100
,0.10 ,0.10 0.54 (0.49)
1 0.7(0.5)m 99.7
0.5 1.0(0.8)m 99.5
0.1 1.3(0.8)m 99.3
Pyriproxyfen 2 0.3(0.3)n 99.9
,0.10 ,0.10
1 0.5(0.4)m 99.8
0.5 0.7(0.6)m 99.7
0.1 0.7(0.6)m 99.7
RH-5849 10 4.7(1.0)l 97.6 2.12 5.26 3.25 (0.29)
7.5 8.7(0.7)k 95.6 (1.80–2.41) (4.79–5.89)
5 18.3(2.2)i 90.7
2.5 83.7(4.8)g 57.6
Tebufenozide 20 7.7(1.0)k 96.1 7.65 13.79 5.00 (0.29)
15 10.3(1.3)j 94.8 (5.97–9.19) (11.29–19.49)
10 53.3(3.5)h 73.0
5 164.7(7.8)f 16.5
Control 0 197.3(6.7)e 0
aThe data are the average of four experiments, each with three replicates. POLO-PC (LeOra Software, 1987) was used for probit analysis. *
Number of normal adults obtained at the end of F1generation period.b% reduction of F1adults emerging compared with control.cLC50, LC90—
concentration levels required for 50 or 90% reduction of F1adults compared with control. 95% confident limits are in parentheses.e–oDifferent
letters indicate statistically significant difference of averages in the same column with 95% confidence.
active on this pest: control of F1 adults was 96% at 20
ppm, and LC50 and LC90 were 7 and 14 ppm,
respect-ively.
3.3. Sitophilus oryzae
The biological activity of the four IGRs on F1
devel-opment of the susceptible laboratory strain of S. oryzae is shown in Table 4. The maximum mortality recorded for parental adults, including the control was 7%. The life span of the F1generation in all treatments including
control was about 42 days, which indicates that, as with
R. dominica, the four IGRs also had no effect on the
life span of S. oryzae. Pyriproxyfen showed very high insecticidal effect: it reduced a number of F1 adults by
97% at 2.5 ppm, and its LC50 and LC90 were only 0.3
and 1.2 ppm, respectively. However, methoprene, RH-5849 and tebufenozide were much less effective for the control of this species: methoprene at 10 ppm, and RH-5849 and tebufenozide at 20 ppm caused reduction of F1adults by only 29, 44 and 40%, respectively. The LC50
and LC90were 13 and 23 ppm for methoprene, 21 and
46 ppm for RH-5849, and for tebufenozide 22 and 32 ppm, respectively.
In summary, comparison among the LC50and LC90of
the four IGRs against the three insects on which they were tested showed that pyriproxifen was the most potent: its LC90 for T. castaneum and R. dominica was
Table 4
The biological activity of various IGRs on development of F1adults of susceptible laboratory strain of Sitophilus oryzaea
IGRs Concentration No. of adults Reduction of F1adults
(ppm) F1(±S.E.M.)* %b LC50(ppm)c LC90(ppm)c Slope (±S.E.M.)
Methoprene 10 163.3(4.9)i 29.3 12.89 23.32 4.98 (0.65)
7.5 203.7(6.4)h 11.8 (11.64–15.16) (18.81–33.32)
5 226.0(11.4)e 2.2
2.5 250.7(10.8)g
28.5
Pyriproxyfen 2.5 6.9(0.8)o 97.0 0.28 1.18 2.06 (0.22)
2 9.0(0.9)n 96.1 (0.20–0.35) (1.03–1.38)
1 27.0(1.6)m 88.3
0.5 72.1(3.0)l 68.8
RH-5849 20 128.9(7.9)k 44.2 21.00 46.48 3.72 (0.45)
15 152.9(8.1)i 33.8
10 207.9(10.7)h 10.0
5 267.3(13.8)f 215.7
Tebufenozide 20 138.7(12.3)j 40.0 21.57 31.71 7.66 (0.83)
15 204.3(9.3)h 11.6 (20.51–23.14) (28.42–37.42)
10 230.1(15.8)e 0.4
Control 0 231.0(13.2)e
aThe data are the average of four experiments, each with three replicates. POLO-PC (LeOra Software, 1987) was used for probit analysis. *
Number of normal adults obtained at the end of F1generation period.b% reduction of F1adults emerging compared with control.cLC50, LC90—
concentration levels required for 50 or 90% reduction of F1adults compared with control. 95% confident limits are in parentheses.e–oDifferent
letters indicate statistically significant difference of averages in the same column with 95% confidence.
Table 5
LC50 and LC90(ppm) of the four IGRs tested on T. castaneum, R. dominica and S. oryzae
IGRs T. castaneum R. dominica S. oryzae
R S S S
LC50 LC90 LC50 LC90 LC50 LC90 LC50 LC90
Pyriproxyfen ,0.1 ,0.1 ,0.1 ,0.1 ,0.1 ,0.1 0.3 1.2 Methoprene 0.8 1.9 ,0.1 ,0.1 ,0.1 ,0.1 13 23
RH-5849 5 7 5 9 2 5 21 46
Tebufenozide 11 15 14 22 8 14 22 32
4. Discussion and conclusions
As expected, the results demonstrated that the four IGRs tested have no effect on parental adults, but, to differing extents, they affect the development of the three economically important insect pests, which attack stored products.
The juvenile hormone agonists methoprene and pyrip-roxyfen have very different influence on the life span of the three species. They had no effect on the life span of
R. dominica and S. oryzae, but very greatly increased
that of T. castaneum. Prolonging larval development leads to the production of supernumerary “giant” larvae, which fail to pupate on treated food and continue to molt as reported by Ishaaya and Yablonski (1976), Rao (1977) and Smet et al. (1989). The larvae of T.
cas-taneum is the most important stage in damaging
com-modities, and the extension of its development and pro-duction of giant larvae would certainly result in more food being consumed. Although treatments with
metho-prene and pyriproxyfen do not kill the larvae of T.
cas-taneum, used at very low concentrations, they can
suc-cessfully prevent the occurrence of F1adults of this pest
as well as of the other two tested species.
The actellic-resistant strain of T. castaneum showed some cross-resistance to methoprene and pyriproxyfen. Methoprene at 0.1 ppm completely inhibited the occur-rence of F1 S-strain adults, but a higher concentration,
of 3 ppm, was necessary to obtain 100% reduction of F1
adults of the R-strain. In addition, at a concentration of 0.1 ppm the life span of the R-strain was 82 days com-pared with 105 days for the S-strain and 67 days for the control. Pyriproxyfen at 0.1 ppm inhibited the develop-ment of F1 adults of both S- and R-strains and it had a
more pronounced effect on the life span of the R-strain than on that of the S-strain. Our studies did not show cross-resistance between the organophosphorus insecti-cide, actellic and the ecdysteroids RH-5849 or tebufeno-zide. However, for definitive conclusions more studies are needed.
Our results show that pyriproxyfen was the most effective compound among the four IGRs tested against three major stored product insects. At 0.1 ppm, it com-pletely inhibited the F1adult occurrence of both S-strain
and R-strain of T. castaneum, and its LC90s for
Methoprene was highly effective against R. dominica. The development of the F1 generation of this pest was
inhibited almost completely at a low concentration of 0.1 ppm. In the case of S. oryzae, methoprene was much less effective: a concentration of 10 ppm caused only 29% reduction of F1 adult number. This result is
sup-ported by studies which showed that methoprene had high potency against R. dominica but low potency against Sitophilus spp. (Daglish and Samson, 1990). Exposing R. dominica to a dose of 1 mg/kg in both lab-oratory and silo tests achieved 100% F1 reduction
(Loschiavo, 1976; Amos and Williams, 1977; Allanson and Wallbank, 1994; Bengston and Strange, 1994). Bengston (1987) reported that 0.125 ppm of methoprene could achieve 100% F1control of R. dominica, but even
at 5 mg/kg, it was ineffective against S. zeamais (Dales et al., 1994). In our studies, we showed that the action of methoprene on the ecdysone-regulated system appeared to affect mainly the larval stage prior to the appearance of the small ecdysteroid peak and the pro-duction of giant hnRNA in the last larval stage prior to pupation (Shaaya 1976,a, 1993). Methoprene is also lethal, through interference with the process of pupal– adult differentiation, when given on the first day after pupation (Shaaya et al., 1986).
RH-5849, the first non-steroidal ecdysone agonist, was found very effective against T. castaneum and R.
dominica, but less active against S. oryzae. At 10 ppm
the percentage reduction in F1adults for S- and R-strains
of T. castaneum, and for R. dominica were 92, 97 and 98%, respectively. However, even at 20 ppm the F1
reduction of S. oryzae was only 44%. This compound has been found, in laboratory and field studies, to have sufficient insecticidal efficacy on a large number of agri-culturally important lepidopteran and coleopteran pests such as Manduca sexta, Plodia interpunctella,
Spodop-tera littoralis, S. frugiperda, S. exempta, Epilachna varivestis, Leptinotarsa decemlineata and Popillia japanica (Wing and Aller, 1990; Ishaaya et al., 1995;
Oberlander et al., 1997). In some experiments, larval growth was inhibited at 5 ppm, and 100% mortality was achieved at 50 ppm (Oberlander et al., 1997). RH-5849 binds to the ecdysteroid receptors, thereby initiating the molting process (Wing et al., 1988), and is effective against both insecticide-susceptible and -resistant pests, and relatively safe to mammals and non-target organisms (Wing and Aller, 1990). Therefore, it should be a viable candidate for the control of T. castaneum and R.
domin-ica.
Oberlander et al. (1997) reported that tebufenozide could inhibit the growth of P. interpunctella at 5 ppm and caused greater than 90% mortality at 10 ppm. It was 10–60 times more potent than RH-5849 for controlling
Spodoptera littoralis larvae (Ishaaya et al., 1995).
How-ever, in our experiments tebufenozide did not show such high efficacy: at 20 ppm the percentage reductions in F1
adults of S- and R-strains of T. castaneum were 80 and 99%, respectively; and LC 90s for R. dominica and S.
oryzae were 14 and 32 ppm, respectively.
Needless to say, that there is an urgent need for environmentally safe alternatives for the two main fumi-gants, which are in use today, for the control of stored product insects, namely phosphine and methyl bromide. Studies have revealed that insects are developing resist-ance to phosphine. Methyl bromide is a compound with ozone-depleting potential and its use in developed coun-tries will prohibit in the year 2005, under the conditions of the Montreal protocol. This situation will have serious impacts on postharvest commodity treatments unless suitable alternatives are developed. The data presented in this study are very useful for the development of such IGRs, which are regarded as potential candidates for the control of stored product insects.
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