Juvenile Hormone Analog Research Articles

Diapause hormone terminates larval diapause in the bamboo borer, Omphisa fuscidentalis (Hampson)

The larvae of the bamboo borer (Omphisa fuscidentalis Hampson) maintain a diapause state for approximately nine months. However, changes in the ecdysteroid titer lead to the termination of larval diapause when juvenile hormone analogue (JHA) is applied. The hormonal mechanisms that terminate larval diapause are still unknown. Recently, it was found that the O. fuscidentalis diapause hormone and pheromone biosynthesis activating neuropeptide genes (Ompfu-DH-PBAN) were expressed during the development of both larvae and pupae and during the late larval diapause. This result suggested that diapause hormone (DH) might be involved in the termination of larval diapause. Thus, our study aims to determine the effect of DH on diapause termination in the bamboo borer. The response of diapausing larvae to DH was assayed using the synthesized O. fuscidentalis diapause hormone (Ompfu-DH). After injection with different concentrations of DH (25, 50 and 100ng/larvae), nearly half of the individual larvae (approximately 45%) became completed or incompleted pupae within 30days. The mean days of pupation in larvae injected with 25, 50 and 100ng DH were 26.81±17.86, 26.30±16.45 and 25.30±16.12, respectively. The hemolymph ecdysteroid titer in Ompfu-DH injected-larvae was significantly higher 10–15days after Ompfu-DH injection and reached a maximum before the formation of the pupal cuticle. These results indicate that Ompfu-DH terminates larval diapause in O. fuscidentalis by increasing the ecdysone in hemolymph, reflecting a new role of DH in the regulation of larval diapause in this species.

A Possible Link between Pyriproxyfen and Microcephaly

The Zika virus is the primary suspect in the large increase in microcephaly cases in 2015-6 in Brazil, however its role is unconfirmed despite individual cases of viral infections found in neural tissue. Here we consider the alternative that the insecticide pyriproxyfen, used in Brazilian drinking water for mosquito control, may actually be the cause. Pyriproxifen is an analog of juvenile hormone, which corresponds in mammals to regulatory molecules including retinoic acid, a vitamin A metabolite, with which it has cross-reactivity and whose application during development causes microcephaly. Methoprene, another juvenile hormone analog approved as an insecticide has metabolites that bind to the retinoid X receptor, and causes developmental disorders in mammals. Isotretinoin is another example of a retinoid causing microcephaly in human babies via activation of the retinoid X receptor. Moreover, tests of pyriproxyfen by the manufacturer, Sumitomo, widely quoted as giving no evidence for developmental toxicity, actually found some evidence for such an effect, including low brain mass and arhinencephaly — incomplete formation of the anterior cerebral hemispheres — in rat pups. Finally, the pyriproxyfen use in Brazil is unprecedented — it has never before been applied to a water supply on such a scale. Claims that it is not being used in Recife, the epicenter of microcephaly cases, do not distinguish the metropolitan area of Recife, where it is widely used, and the municipality, where it is not. Given this combination of information we strongly recommend that the use of pyriproxyfen in Brazil be suspended pending further investigation.

Juvenile hormone regulates the differential expression of putative juvenile hormone esterases via methoprene-tolerant in non-diapause-destined and diapause-destined adult female beetle

Juvenile hormone (JH) plays an essential role in regulating molting, metamorphosis, reproduction, and diapause (dormancy), in many insects and crustaceans. JH esterases (JHEs) can control JH titer by regulating JH degradation. Although the biochemistry and structure of JHEs have been well studied, regulation of their expression remains unclear. We identified three putative JHEs (JHE1, JHE2, JHE3) in the cabbage beetle Colaphellus bowringi, and investigated the regulation of their expression by JH signaling in non-diapause-destined (NDD, reproductive) and diapause-destined (DD) female adults. Sequence and phylogenetic tree analyses indicate that the three putative JHEs shared conserved motifs with the JHEs of other insects and one crustacean, and were similar to Coleopteran, Dipteran, Orthopteran, Hymenopteran, and Decapodan JHEs. They were, however, less closely related to Hemipteran and Lepidopteran JHEs. JHEs were more highly expressed in NDD female adults than in DD female adults. JH analog induction in DD female adults significantly upregulated the expression of JHE1 and JHE2, but had no effect on the expression of JHE3. Knockdown of the JH candidate receptor methoprene-tolerant (Met) in NDD female adults downregulated the expression of all three JHEs. These results suggest that JHE expression is positively correlated with JH signaling, and that Met may be involved in the JH-mediated differential expression of JHE in DD and NDD adult female C. bowringi.

Insecticides on the basis of analogs of insect juvenile hormones

Analogs of juvenile hormones (JHAs)—azadirachtin (NeemAzal, EC (10 g/L), fenoxycarb (Phasis, WP (250 g/kg), and pyriproxyfen (Admiral, EC (100 g/L) and Inoxyfen, EC (100 g/L)—have been tested. The effectiveness of insectoacaricide NeemAzal in regulating the population numbers of sucking insects was assessed using glasshouse cucumber in Leningrad oblast. Three applications of this product in 0.5% concentration effectively protected this culture against red spider mite (Tetranychus urticae Koch.) and onion thrips (Thrips tabaci Lind) and, less significantly, against melon aphid (Aphis gossypii Glov). Insecticide Phasis protected vineyards against European vine moth (Lobesia botrana Den&Schiff). Juvenoid Admiral effectively decreased the number of imagoes and larvae of greenhouse whitefly (Trialeurodes vaporariorum Wsfw.) in glasshouse cucumber and tomato in different regions of Russia, while Inoxyfen protected apples against codling moth (Cydia pomonella). The tested products belong to the group of biorational pesticides that can be used in ecologically sound systems of plant protection.

The FOXO transcription factor controls insect growth and development by regulating juvenile hormone degradation in the silkworm, Bombyx mori

Forkhead box O (FOXO) functions as the terminal transcription factor of the insulin signaling pathway and regulates multiple physiological processes in many organisms, including lifespan in insects. However, how FOXO interacts with hormone signaling to modulate insect growth and development is largely unknown. Here, using the transgene-based CRISPR/Cas9 system, we generated and characterized mutants of the silkworm Bombyx mori FOXO (BmFOXO) to elucidate its physiological functions during development of this lepidopteran insect. The BmFOXO mutant (FOXO-M) exhibited growth delays from the first larval stage and showed precocious metamorphosis, pupating at the end of the fourth instar (trimolter) rather than at the end of the fifth instar as in the wild-type (WT) animals. However, different from previous reports on precocious metamorphosis caused by juvenile hormone (JH) deficiency in silkworm mutants, the total developmental time of the larval period in the FOXO-M was comparable with that of the WT. Exogenous application of 20-hydroxyecdysone (20E) or of the JH analog rescued the trimolter phenotype. RNA-seq and gene expression analyses indicated that genes involved in JH degradation but not in JH biosynthesis were up-regulated in the FOXO-M compared with the WT animals. Moreover, we identified several FOXO-binding sites in the promoter of genes coding for JH-degradation enzymes. These results suggest that FOXO regulates JH degradation rather than its biosynthesis, which further modulates hormone homeostasis to control growth and development in B. mori In conclusion, we have uncovered a pivotal role for FOXO in regulating JH signaling to control insect development.

Methoprene and Temperature Stimulation of Emergence and Longevity in Adults of Osmia Rufa L. (Megachilidae; Apoidea) During Wintering Period

Abstract In this study methoprene, a juvenile hormone analogues, was tested as a factor that stimulates the end of diapause, bee activation and emergence. In addition, the survival of bees was checked when combined with an application of methoprene. The experimental activation of wintering bees was carried out once a month between December and March, Three groups of bee cocoons were selected for each activation term: treated with either methoprene or acetone as vehicle control and untreated as controls. After the applications were finished the cocoons were incubated at temperature 26°C. The emerged adult males and females were then kept in the laboratory and fed sucrose solution to evaluate the longevity of bees. The application of juvenile hormone analogue reduced the emergence time of adult bees in December, February and March. The rate of emergence presented in the form of cumulative percentage of emerged adult bees indicated that the bees treated with methoprene started to emerge 1-2 days earlier than bees from acetone and control groups and finished emergence 2-5 days earlier too. Methopren application did not reduce the longevity of the bees after emergence. Moreover, the median longevity of these females was higher than untreated in December and February.

Phenotypic defects in newborn Gammarus fossarum (Amphipoda) following embryonic exposure to fenoxycarb

During morphogenesis numerous morphogenetic factors ensure the production of a target phenotype. By disrupting these processes, a toxic exposure during this period could cause an increase of phenotypic defects. In the present study, embryos of the freshwater amphipod Gammarus fossarum were exposed throughout the embryogenesis to increasing concentrations of fenoxycarb (0, 0.5µgL−1, 5µgL−1 and 50µgL−1), a growth regulator insecticide analog of the insect juvenile hormone. In addition, to identify morphogenesis’ sensitive period, embryos were exposed during either early or late embryonic development to 5µgL−1 of fenoxycarb. In newborn individuals from exposed embryos, three phenotypes were investigated: i) eye pigmentation, ii) length of the antenna and gnathopod of both left and right sides and iii) midgut tissue state. Developmental homeostasis was assessed by measuring fluctuating asymmetry and inter-individual variance of both the antenna and gnathopod. Exposure to 5µgL−1 and 50µgL−1 fenoxycarb throughout the embryonic development induced a delayed hatching and altered appendages size. Moreover, exposure to 5µgL−1 throughout the embryogenesis and during the gastrulation phase impaired eye pigmentation, while exposure to 50µgL−1 resulted in increased tissue damages of the midgut. No significant increase of fluctuating asymmetry was observed in exposed individuals, neither for the antenna nor for the gnathopod. These results demonstrate that fenoxycarb can alter embryonic development of G. fossarum without disrupting developmental homeostasis.

Pyriproxyfen treatment terminates Halyomorpha halys reproductive diapause, with an indirect mortality effect on its egg parasitoid Trissolcus japonicus

The success of Halyomorpha halys (Stal) as an invasive species in temperate climates is partly due to its ability to survive winter in a state of reproductive diapause. In H. halys, the termination of juvenile hormone (JH) production by the corpora allata, in response to a decline in day length, leads to the initiation of diapause and suspension of reproductive activity. Results of this study showed that topical application of the JH analog pyriproxyfen at doses of 0.05–100 μg per insect resulted in the resumption of oocyte formation and oviposition in a dose-dependent manner, with the ED50 estimated at 1.14 μg per insect. Eggs induced by pyriproxyfen application had significantly lower hatchability than control eggs. The indirect effects of host exposure to pyriproxyfen on the hymenopteran parasitoid Trissolcus japonicus (Ashmead), a candidate biological control agent of H. halys, were evaluated. When presented with eggs produced by pyriproxyfen-treated females, T. japonicus was observed ovipositing, but no adult parasitoids emerged from host eggs. Exposure to pyriproxyfen has the potential to lower the reproductive potential of H. halys populations by inducing the production of eggs with reduced viability during periods of low resource availability. The complete mortality of T. japonicus developing on pyriproxyfen-induced eggs suggests that insect growth regulators which interfere with host reproduction may exert a strong indirect effect on beneficial egg parasitoids, and may not be compatible with egg parasitoid biological control programs.

Evaluation of fluνalinate, methomyl and kinoprene on the greenhouse whitefly Trialeurodes vaporariorum West. (Homoptera: Aleyrodidae)

The effectiveness of three insecticides, fluvalinate, kinoprene and methomyl (synthetic pyrethrin, juvenile hormone analog and organophosphate, respectively), against the greenhouse whitefly, Trialeurodes vaporariorum West. (Homoptera: Aleyrodidae), was evaluated in commercial greenhouses. The impact of chemicals was studied on isolated whitefly stages in a rearing room (24 ± I”C, 65 ± 5% R.H. and L:D 16:8h). Fluvalinate was the most effective toxicant through its broad activity on whitefly life stages. Kinoprene controlled 2nd and 3rd larval instars but a moderate effectiveness was noticed on eggs, first instar larvae and pupae. Methomyl was effective against first instar larvae and adults but it had no substantial effect on the other stages. Of the three materials tested only fluvalinate approached the total control requirements for a successful whitefly suppression.

Effects of juvenile hormone analogue (methoprene) and 20-hydroxyecdysone on reproduction in Polygonia c-aureum (Lepidoptera: Nymphalidae) in relation to adult diapause.

We investigated the effects of juvenile hormone analogue (methoprene) and 20-hydroxyecdysone on female and male reproduction in a nymphalid butterfly, Polygonia c-aureum. This butterfly has a facultative adult diapause controlled by the corpora allata and brain. Methoprene seems to terminate reproductive diapause, although transplantation experiments indicate that the activity of the corpora allata does not affect male mating behavior Endo (Dev Growth Differ 15:1-10, 1973a), suggesting that the brain may be involved in diapause. We found that exposure to methoprene promoted the development of ovaries and of the male accessory glands and simplex. On the other hand, exposure to 20-hydroxyecdysone did not promote the development of female and male reproductive organs and eupyrene sperm movement from the testis to the duplex in the adult stage. Ecdysteroid titer in both sexes was consistently low in adults. These results suggest that imaginal diapause is largely regulated by juvenile hormone in this butterfly.

Juvenile hormone analogue, fenoxycarb, modulates ecdysone-triggered transcriptional hierarchy during programmed cell death of midgut in silkworm, Bombyx mori (Lepidoptera: Bombycidae)

Steroid hormone 20-hydroxyecdysone and the sesquiterpenoid juvenile hormone are the main regulators of insect development; however, it is unclear how they interact in the regulation of metamorphic events. Using the silkworm, Bombyx mori, we show that the juvenile hormone analogue fenoxycarb affects the cascade of ecdysone regulated genes that control the programmed cell death in the larval midgut. Morphological changes that occur during cell death were investigated by studying cross-sections of the midgut stained with hematoxylin and eosin. Apoptosis-specific DNA fragmentation was detected using TUNEL assay. Expression patterns of genes ATG8 and ATG12, which were used as indicators of autophagy, and genes of the ecdysone-regulated gene cascade were examined using real-time quantitative polymerase chain reaction. Fenoxycarb application on day 0 of the 5th larval instar extended the feeding period and postponed programmed cell death in mature larval midgut. This effect was probably due to a delay in ecdysone secretion and associated changes in gene expression were mostly not a direct response to the fenoxycarb. However, differences in the gene expression patterns in the control and fenoxycarb treated insects during the prepupal and early pupal stages indicated that fenoxycarb may also exert a more direct effect on some genes of the ecdysone regulated gene cascade.

A larval ‘princess pheromone’ identifies future ant queens based on their juvenile hormone content

Numerous studies have identified cuticular compounds that distinguish adult queens from workers in social insect colonies, but how future queens are identified at the larval stage is poorly understood. Nevertheless, the ability of workers to discriminate queen and worker larvae is necessary for them to regulate caste determination and queen production. In the ant Harpegnathos saltator, workers bite larvae to inhibit queen development, and we used biting as an assay to test how workers identify queens at the larval stage. The transfer of cuticular compounds from queen to worker larvae through direct physical contact (rubbing) or using a hexane extract both elicited biting. Gas chromatography revealed significant differences in cuticular hydrocarbon profiles of queen and worker larvae that could be induced by treatment with a juvenile hormone (JH) analogue. Finally, treatment of male larvae with a JH analogue also elicited worker biting, which suggests a direct connection between JH levels and the production of a larval queen signal. These results demonstrate that workers identify larval caste using a chemical signal present on the cuticle, a ‘princess pheromone’, that reflects endocrine changes associated with queen development. Based on the connection between JH levels and the production of a larval queen signal, we developed a model for caste determination in H. saltator that incorporates endocrine, pheromonal and behavioural control of caste development.

Modulation of Juvenile Hormone Analogue (Jha) Mimic on Larval Instars of Tropical Tasar Silk Insect (Lepidoptera: Saturniidae) to Elucidate the State of Silk Performance Parameters

Modulation of Juvenile Hormone Analogue (Jha) Mimic on Larval Instars of Tropical Tasar Silk Insect (Lepidoptera: Saturniidae) to Elucidate the State of Silk Performance Parameters

Larval diapause termination in the bamboo borer, Omphisa fuscidentalis.

In insects, juvenile hormone (JH) and 20-hydroxyecdysone (20E) regulate larval growth and molting. However, little is known about how this cooperative control is terminating larval diapause especially in the bamboo borer, Omphisa fuscidentalis. In both in vivo and in vitro experiments, we here measured the expression levels of genes which were affected by juvenile hormone analogue (JHA: S-methoprene) and 20-hydroxyecdysone (20E) in diapausing O. fuscidentalis larvae. Corresponding mRNA expression changes in the subesophageal ganglion (SG) and prothoracic gland (PG) were evaluated using qRT-PCR. The data showed similar response patterns of JH receptor gene (OfMet), diapause hormone gene (OfDH-PBAN), ecdysone receptor genes (OfEcR-A and OfEcR-B1) and ecdysone inducible genes (OfBr-C, OfE75A, OfE75B, OfE75C and OfHR3). JHA induced the expressions of OfMet and OfDH-PBAN in both SG and PG, whereas ecdysone receptor genes and ecdysone inducible genes were induced by JHA only in PG. For 20E treatment group, expressions of ecdysone receptor genes and ecdysone inducible genes in both SG and PG were increased by 20E injection. In addition, the in vitro experiments showed that OfMet and OfDH-PBAN were up-regulated by JHA alone, but ecdysone receptor genes and ecdysone inducible genes were up-regulated by JHA and 20E. However, OfMet and OfDH-PBAN in the SG was expressed faster than OfMet and OfDH-PBAN in the PG and the expression of ecdysone receptor genes and ecdysone inducible genes induced by JHA was much later than observed for 20E. These results indicate that JHA might stimulate the PG indirectly via factors (OfMet and OfDH-PBAN) in the SG, which might be a regulatory mechanism for larval diapause termination in O. fuscidentalis.

Pyriproxyfen inhibits the suppressive effect of inflammatory signal on TR4 activity

AbstractObesity causes a chronic inflammatory state by increasing secretion of proinflammatory cytokines such as tumor necrosis factor alpha (TNFα), which alters signaling pathways critical for metabolic homeostasis, leading to obesity‐related metabolic disorders. Here, we demonstrate that TNFα inhibits testicular orphan nuclear receptor 4 (TR4) transcriptional activity and this TNFα inhibition of TR4 activity is reduced by treatment of Pyriproxyfen (PYR), a juvenile hormone (JH) analog. In addition, nuclear factor‐kappa B (NF‐κB), a key transcription regulator of inflammation, also suppressed TR4 transactivation by physical interaction with TR4, reducing TR4 binding affinity for TR4 response elements located in its target gene promoters. Consistently, NF‐κB‐suppressed TR4 activity was partially restored by PYR treatment. Furthermore, TNFα inhibited mRNA levels of TR4 target genes such as, FATP1 and PC with reduction of lipid accumulation in 3 T3‐L1 adipocytes while PYR suppressed TNFα inhibition of TR4 target gene expression, resulting in recovery of lipid accumulation of adipocytes, suggesting that PYR enhances lipid homeostasis disturbed by inflammatory signaling and this PYR effect could be achieved in part by stimulating TR4 transcriptional activity. Together, our data show that PYR regulates inflammatory signaling in adipocytes and thus, small molecules based on insect hormones could be an alternative approach to control obesity‐related metabolic disorders.

Abnormal development in larvae of Sesamia nonagrioides (Lepidoptera: Noctuidae) resulting from baculovirus-mediated overexpression of a JHE-related gene (SnJHER)

The Mediterranean corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae) has a unique and recently multiplied juvenile hormone esterase gene family (SnJHER) with particular transcriptional profiles and functional characteristics. Unlike conventional juvenile hormone esterase genes (JHEs), the SnJHER gene family seems to have been recently evolved from a common ancestral JHER gene. SnJHERs seem to be regulated by both ecdysone agonists and xenobiotics, while their real role in development remains to be exploited. In this study we transiently expressed the major SnJHER isoform in Bm5 and Hi5 cell lines. The JHER-expressing cell lines showed increased toxicity when treated with the juvenile hormone analog methoprene. Moreover baculovirus-mediated transient gene transduction of the SnJHER gene in larvae of S. nonagrioides resulted in moulting abnormalities. These were more marked after the additional application of the juvenile hormone analog methoprene. Our results indicate a potential mechanism by which SnJHER interferes with normal JHE.

A Possible Link Between Pyriproxyfen and Microcephaly.

The Zika virus has been the primary suspect in the large increase in incidence of microcephaly in 2015-6 in Brazil. While evidence for Zika being the cause of some of the cases is strong, its role as the primary cause of the large number of cases in Brazil has not been confirmed. Recently, the disparity between the incidences in different geographic locations has led to questions about the virus's role. Here we consider the alternative possibility that the use of the insecticide pyriproxyfen for control of mosquito populations in Brazilian drinking water is the primary cause. Pyriproxifen is a juvenile hormone analog which has been shown to correspond in mammals to a number of fat soluble regulatory molecules including retinoic acid, a metabolite of vitamin A, with which it has cross-reactivity and whose application during development has been shown to cause microcephaly. Methoprene, another juvenile hormone analog that was approved as an insecticide based upon tests performed in the 1970s, has metabolites that bind to the mammalian retinoid X receptor, and has been shown to cause developmental disorders in mammals. Isotretinoin is another example of a retinoid causing microcephaly in human babies via maternal exposure and activation of the retinoid X receptor in developing fetuses. Moreover, tests of pyriproxyfen by the manufacturer, Sumitomo, widely quoted as giving no evidence for developmental toxicity, actually found some evidence for such an effect, including low brain mass and arhinencephaly—incomplete formation of the anterior cerebral hemispheres—in exposed rat pups. Finally, the pyriproxyfen use in Brazil is unprecedented—it has never before been applied to a water supply on such a scale. Claims that it is not being used in Recife, the epicenter of microcephaly cases, do not distinguish the metropolitan area of Recife, where it is widely used, and the municipality, and have not been adequately confirmed. Given this combination of information about molecular mechanisms and toxicological evidence, we strongly recommend that the use of pyriproxyfen in Brazil be suspended until the potential causal link to microcephaly is investigated further.

Methoprene does not affect juvenile hormone titers in honey bee (Apis mellifera) workers.

Methoprene, a juvenile hormone (JH) analog, is a widely used insecticide that also accelerates behavioral development in honey bees (Apis mellifera). JH regulates the transition from nursing to foraging in adult worker bees, and treatment with JH or methoprene have both been shown to induce precocious foraging. To determine how methoprene changes honey bee behavior, we compared JH titers of methoprene-treated and untreated bees. Behavioral observations confirmed that methoprene treatment significantly increased the number of precocious foragers in 3 out of 4 colonies. In only 1 out of 4 colonies, however, was there a significant difference in JH titers between the methoprene-treated and control bees. Further, in all 4 colonies, there was no significant differences in JH titers between precocious and normal-aged foragers. These results suggest that methoprene did not directly affect the endogenous JH secreted by corpora allata. Because methoprene caused early foraging without changing workers' JH titers, we conclude that methoprene most likely acts directly on the JH receptors as a substitute for JH.

Serine proteinase (SP) and serine protease inhibitor (serpin) gene expression after hormone treatment in the silkworm Bombyx mori (Lepidoptera: Bombycidae)

Many members of the Serine protease inhibitor (serpin) family participate in regulation by inhibiting Serine proteinases (SPs) or Serine protease homologs (SPHs) isozymes and maintaining the balance in the internal environment. SPs were expressed in the midguts of mid-fifth-instars and exhibited slightly higher expression in female compared to male late-fifth-instars. However, serpins were mainly expressed in the silk glands, achieved a higher level of expression in the late fifth-instar and had an expression advantage in the males. The ratio of the cocoon shell was significantly higher in Jingsong compared to the other varieties in both the males and females, which was consistent with the higher mRNA and protein expression of Spi1 in the silk gland of Jingsong compared to the other varieties. These results reflected the positive correlation between TRP protein expression and the ratio of the cocoon shell and suggested that the higher mRNA and protein expression levels of the serpin gene was molecular evidence of more efficient silk material synthesis. The SP/SPH and serpin genes presented different regulatory trends after treatment of the day 3 fifth-instar silkworm larvae with 20-hydroxyecdysone (20E) and juvenile hormone analogues (JHA). The majority of the surveyed SP/SPH genes were down-regulated and serpin genes were up-regulated under treatment with the high concentration 20E. After JHA treatment, all of the investigated genes were up-regulated 48h after treatment with JHA. The hormone regulatory effect was primarily influenced by the developmental stage and the hormone dose. The tissue specificity and sex differences in the SP/SPH and serpin genes implied that they participated in tissue-specific transcriptional regulation. The genes were expressed at different levels during different developmental periods and following hormone treatment. The results demonstrated that the genes played a role in scheduling and provided insights into the mechanism underlying silk material formation and accumulation.

Reproductive Cost Associated With Juvenile Hormone in Bt-Resistant Strains of Helicoverpa armigera (Lepidoptera: Noctuidae).

Transgenic Bacillus thuringiensis (Bt) crops are increasingly significant in pest control, but resistance development of target pests is a major issue in the sustainable deployment of Bt crops. The fitness cost of resistance in target pests is regarded as one of the main factors delaying resistance when adopting the refuge strategy. In this study, we compared the life-history traits of three independent sets of Helicoverpa armigera (Hübner, 1809) adults, of each there were a susceptible population and a Cry1Ac-resistant population derived by selection from it. Confirming to the previous studies, resistant individuals exhibited fewer progeny, less fecundity, lower egg hatching rate, and longer adult longevity. And poor fecundity in resistant strains was associated with the decline of the mature follicular amount, the ovarian weight ratio, and the length of the longest ovarian tubule. Interestingly, the juvenile hormone (JH) level appeared higher in resistant strains relative to susceptible strains. Application of methoprene (JH analogue) in vivo was effective in reducing fecundity and hatchability with the up-regulation of detected JH titer. These results suggested that resistance against Bt toxin reduced the reproductive capacity of H. armigera, and JH level is affected in the tradeoff between reproductive capacity and Bt resistance.