Mobility is related to species traits in noctuid moths

1. Mobility is important for the understanding of how species survive in fragmented landscapes and cope with increasing rates of habitat and climate change. However, mobility is a difficult trait to explore and is poorly known in most taxa. Species traits have been studied in relation to range shifts, extinction risks, and responses to habitat area and isolation, and have also been suggested as good estimators of mobility. Here we explore the relation between mobility and species traits in noctuid moths. 2. We sampled noctuid moths by an automatic light‐trap on an island far out in the Baltic Sea. We compared traits of the non‐resident species on the island with traits of a species pool of assumed potential migrants from the Swedish mainland. 3. Mobility was significantly related to adult activity period, length of flight period, and the interaction between host‐plant specificity and distribution area. Widely distributed host‐plant generalists were more mobile than host‐plant specialists with more restricted distribution, and species with an adult activity period in August to September moved to the island to a higher extent than species with an adult activity period in May to July. Our results remained qualitatively robust in additional analyses, after controlling for phylogeny and including all species recorded on the island, except for the trait ‘length of flight period’. 4. Our results highlight the importance of the relation between mobility and species traits. Noctuid moths with certain traits move over longer distances than earlier known. This finding is important to include when predicting range dynamics in fragmented and changing landscapes, and when conservation measures of species are devised.     

Regulation of migration in Mythimna separata (Walker) in China: a review integrating environmental, physiological, hormonal, genetic, and molecular factors

Each year the Mythimna separate (Walker), undertakes a seasonal, long-distance, multigeneration roundtrip migration between southern and northern China. Despite its regularity, the decision to migrate is facultative, and is controlled by environmental, physiological, hormonal, genetic, and molecular factors. Migrants take off on days 1 or 2 after eclosion, although the preoviposition period lasts ≈7 d. The trade-offs among the competing physiological demands of migration and reproduction are coordinated in M. separata by the "oogenesis-flight syndrome." Larvae that experience temperatures above or below certain thresholds accompanied by appropriate humidity, short photoperiod, poor nutrition, and moderate density tend to develop into migrants. However, there is a short window of sensitivity within 24 h after adult eclosion when migrants can be induced to switch to reproductive residents if they encounter extreme environmental factors including starvation, low temperature and long photoperiod. Juvenile hormone (JH) titer is low before migration but high titers are associated with termination of migratory behavior and the switch to reproduction. Early release of JH by the corpora allata in environmentally stressed 1-d old adults, otherwise destined by larval conditions to be migrants, switches them to residents. Offspring inherit parental additive genetic effects governing migratory behavior. However, they also retain flexibility in expression of both flight and reproductive life history traits. The insect neuropeptide, allatotropin, which activates corpora allata to synthesize JH, controls adult flight and reproduction. Future research directions to better understand regulation of migration in this species are discussed.     

Hemolymph juvenile hormone titers in pupal and adult stages of southwestern corn borer [Diatraea grandiosella (pyralidae)] and relationship with egg development

Juvenile hormones I, II and III were monitored in hemolymph of pupal and adult stages of various ages of Diatraea grandiosella females. JH III was the predominant homologue followed by JH II, and JH I was rarely detectable. At day 5 after pupation, no JH was detectable. JH titers increased from 7.5days after pupation to a peak of 24.8ngml(-1) JH II and 26ngml(-1) JH III at adult emergence and then declined to low levels by 24h after emergence. Ovarian development in D. grandiosella parallels changes in hemolymph JH titers, but the role of JH in vitellogenesis is unclear since the time of vitellogenesis initiation has yet to be determined. No apparent vitellogenin deposition was observed in eggs 5days after pupation. Some oocytes were partially vitellogenic by 7.5days after pupation and oocytes continued to grow afterwards, but no oocytes were chorionated during the pupal stage. Chorionated oocytes were observed in 24-h-old female moths. Juvenile hormone is essential for chorion formation in this species, because decapitated pupae treated with 10&mgr;g JH III in corn oil developed chorionated oocytes while decapitated pupae treated with corn oil did not.     

Identification of the juvenile hormones from adult Attacus atlas

Both juvenile hormone (JH) II and JH I have been identified in whole body extracts of the atlas moth, Attacus atlas. In 0–24 hr old adult males, levels of JH II were ∼ 15 ng/g while JH I titers were much lower (∼0.4 ng/g). In keeping with titer data obtained from other Saturniid moths, male animals contained substantially more JH than adult females, which contained <0.1 ng/g of predominantly JH II. Our results are in contrast to a prior study which did not detect any of the known JHs and hinted at the possible existence of a new JH active principle. The levels of JH I plus II we detected in A. atlas can easily account for the amount of biological activity observed in the prior study. Hence, we are confident that JH II and JH I constitute the only JHs of adult A. atlas.     

The endocrine regulation of wing polymorphism in insects: state of the art, recent surprises, and future directions

The endocrine mechanisms controlling the development and reproduction of flight-capable (long-winged) and flightless (short-winged or wingless) morphs of wing-polymorphic insects have been intensively investigated. The "classical model," put forward in the early 1960s, postulates that morph-specific differences in development and reproduction are caused by variation in the titers of juvenile hormone (JH) and/or ecdysone. Despite decades of study, the importance of these hormones in regulating wing polymorphism in aphids and planthoppers remains uncertain. This uncertainly is largely a consequence of technical and size constraints which have severely limited the types of endocrine approaches that can be used in these insects. Recent studies in wing-polymorphic crickets (Gryllus) have provided the first direct evidence that the in vivo blood titers of juvenile hormone and ecdysone, and especially the activity of the JH regulator, juvenile hormone esterase, differ between nascent morphs. Morph differences are largely consistent with the classical model, although some types of data are problematic, and other explanations are possible. Adult morphs differ dramatically in the JH titer but titer differences are more complex than those proposed by the classical model. Detailed endocrine information is thus far available only for a few species of crickets, and the hormonal control of wing polymorphism for insects as a whole remains poorly understood. Future studies should continue to investigate the role of JH and ecdysteroids in morph development and reproduction, and should expand to include studies of morph-specific differences in hormone receptors and neurohormones.     

Juvenile hormone titers in virgin and mated Choristoneura fumiferana and C. rosaceana females: assessment of the capacity of males to produce and transfer JH to the female during copulation

We used a radioimmunoassay (RIA) to assess the effect of mating on juvenile hormone (JH) titer in females of the tortricid moths Choristoneura fumiferana and C. rosaceana. Virgins had undetectable levels of JH in their hemolymph on the 5th day of the pupal stage but titers rose to 1-4 and 0.2-0.5 ng JH II eq./ml, respectively, after emergence. On days 1, 3 and 5 following copulation, females of both species had higher JH titers than virgins of the same ages, with the greatest difference between virgin and mated females observed on day 3 for C. fumiferana and on day 5 for C. rosaceana. This increase was apparently not the result of a male-to-female transfer of JH during copulation since: (i) the accessory sex glands (ASGs) of males of both species displayed a very limited ability to convert JH acid into JH, (ii) ASGs produced no JH when incubated in vitro in the presence of L-[methyl-(3)H]-methionine, (iii) ASGs of males injected with L-[methyl-(3)H]-methionine 24 h prior to dissection contained no JH-associated radioactivity, and (iv) freshly formed spermatophores dissected out of females mated to similarly injected males contained no trace of radioactive JH. In addition, the JH content of ASGs and spermatophores, as measured by RIA, was not higher than that of virgin-female hemolymph, on a per-mg basis. However, in contrast with earlier findings in other species of moths, the CA of male C. fumiferana and C. rosaceana maintained in vitro in the presence of tritiated methionine produced and released JH I, JH II and JH III in quantities and proportions similar to those reported for female glands.     

Functional analysis of the allatostatin-A type gene in the cricket Gryllus bimaculatus and the armyworm Spodoptera frugiperda

Double-stranded RNA (dsRNA) gene interference is an efficient method to silence gene expression in a sequence specific manner. Here we show, that dsRNA targeting the allatostatin (AS)-A type (FGL/I/V-amide) gene of Gryllus bimaculatus (Ensifera, Gryllidae) and Spodoptera frugiperda (Lepidoptera, Noctuidae) injected into freshly moulted larvae or adult crickets and moths produced a rapid and long-lasting reduction in the mRNA levels in various tissues. The effect lasted up to 7 days. Following dsRNA injection, the juvenile hormone (JH) titers in the hemolymph were clearly raised in both species. AS-dsRNA injection induced a reduced body weight in larval and adult crickets and the imaginal moult was incomplete. Silencing allatostatin type-A expression also reduced the egg and testes development in crickets, and the oviposition rate was drastically diminished in both species.     

Juvenile hormone titer and morph-specific reproduction in the wing-polymorphic cricket,Gryllus firmus

Juvenile hormone titers and reproductive characteristics were measured in adult wing and flight-muscle morphs of the wing-polymorphic cricket, Gryllus firmus, during the first week of adulthood. This species has three morphs: one flight capable morph with fully-developed wings and fully-developed flight muscles [LW(F)], one flightless morph with fully-developed wings and histolyzed (non-functional) flight muscles [LW(H)], and another flightless morph with underdeveloped (short) wings and underdeveloped flight muscles (SW). Both flightless morphs [LW(H) and SW] had larger ovaries which contained a greater number of postvitellogenic eggs compared with the flight capable [LW(F)] morph. The juvenile hormone titer was significantly higher in SW compared with LW(F) females on days 3-7 of adulthood. On these days, the JH titer also was significantly higher in the other flightless morph, LW(H), compared with flight-capable [LW(F)] females as determined by one statistical test, but did not differ significantly by another test. The JH titer was positively correlated with ovarian mass or terminal oocyte length, but not with the number of post-vitellogenic eggs. This study is the first direct comparison of juvenile hormone titers in adult wing morphs of a wing-polymorphic insect. Results indicate that an elevated juvenile hormone titer may be at least partly responsible for one of the most distinctive features of wing-polymorphic species, the increased early fecundity of flightless females.     

Larval juvenile hormone treatment affects pre-adult development,but not adult age at onset of foraging in worker honey bees (Apis mellifera)

Previous research has shown that juvenile hormone (JH) titers increase as adult worker honey bees age and treatments with JH, JH analogs and JH mimics induce precocious foraging. Larvae from genotypes exhibiting faster adult behavioral development had significantly higher levels of juvenile hormone during the 2nd and 3rd larval instar. It is known that highly increased JH during this period causes the totipotent female larvae to differentiate into a queen. We treated third instar larvae with JH to test the hypothesis that this time period may be a developmental critical period for organizational effects of JH on brain and behavior also in the worker caste, such that JH treatment at a lower level than required to produce queens will speed adult behavioral development in workers. Larval JH treatment did not influence adult worker behavioral development. However, it made pre-adult development more queen-like in two ways: treated larvae were capped sooner by adult bees, and emerged from pupation earlier. These results suggest that some aspects of honey bee behavioral development may be relatively insensitive to pre-adult perturbation. These results also suggest JH titer may be connected to cues perceived by the adult bees indicating larval readiness for pupation resulting in adult bee cell capping behavior.     

Activity of the corpora allata of adult female Leucophaea maderae: effects of mating and feeding

Juvenile hormone III biosynthesis by corpora allata of adult female Leucophaea maderae was measured by an in vitro radiochemical assay. In fed females, JH III synthesis increases more than 20-fold after mating to a peak of 55 pmol/pair/h on day 9 and then rapidly declines. This increase in JH III synthesis concomitant with rapid oocyte growth in mated females is not observed in virgin females. The corpora allata from starved, virgin females appear to be inactive. The addition of 150 microM 2E,6E-farnesol (a) JH III precursor) to the incubation medium stimulates the corpora allata from starved, virgin females less than the corpora allata from starved, mated females. Both feeding and mating are necessary for the expression of a normal cycle of JH III synthesis in this cockroach.     

Hormones in the field: evolutionary endocrinology of juvenile hormone and ecdysteroids in field populations of the wing-dimorphic cricket Gryllus firmus

Virtually no published information exists on insect endocrine traits in natural populations, which limits our understanding of endocrine microevolution. We characterized the hemolymph titers of juvenile hormone (JH) and ecdysteroids (ECDs), two key insect hormones, in field-collected short-winged, flightless (SW) and long-winged, flight-capable (LW(f)) morphs of the cricket Gryllus firmus. The JH titer exhibited a dramatic circadian rhythm in the LW(f) morph but was temporally constant in the flightless SW morph. This pattern was consistent in each of three years; in young, middle-aged, and older G. firmus; and in three other cricket species. The ECD titer was considerably higher in SW than in LW(f) females but did not exhibit temporal variation in any morph and did not differ between male morphs. JH and ECD may control different aspects of the morph-specific trade-off between nocturnal dispersal and reproduction. Results confirm and extend laboratory studies on young female G. firmus; most, but not all, important aspects of morph-specific differences in JH and ECD titers can be extrapolated from field to laboratory environments and vice versa. Hormone titers in Gryllus are more complex than those proposed in evolutionary endocrine models. Directly measuring hormone titer variation remains a fundamentally important task of insect evolutionary endocrinology.     

Juvenile Hormone and Insulin Regulate Trehalose Homeostasis in the Red Flour Beetle,Tribolium castaneum

Insulin/IGF-1 signaling (IIS) has been well studied for its role in the control of life span extension and resistance to a variety of stresses. The Drosophila melanogaster insulin-like receptor (InR) mutant showed extended life span due to reduced juvenile hormone (JH) levels. However, little is known about the mechanism of cross talk between IIS and JH in regulation of life span extension and resistance to starvation. In the current study, we investigated the role of IIS and JH signaling in regulation of resistance to starvation. Reduction in JH biosynthesis, JH action, or insulin-like peptide 2 (ILP2) syntheses by RNA interference (RNAi)-aided knockdown in the expression of genes coding for juvenile hormone acid methyltransferase (JHAMT), methoprene-tolerant (Met), or ILP2 respectively decreased lipid and carbohydrate metabolism and extended the survival of starved beetles. Interestingly, the extension of life span could be restored by injection of bovine insulin into JHAMT RNAi beetles but not by application of JH III to ILP2 RNAi beetles. These data suggest that JH controls starvation resistance by regulating synthesis of ILP2. More importantly, JH regulates trehalose homeostasis, including trehalose transport and metabolism, and controls utilization of stored nutrients in starved adults.     

一日龄饥饿对粘虫成虫卵巢发育和飞行能力的影响

为了明确羽化后0～24 h (1日龄)饥饿处理对迁飞型粘虫Mythimna separata (Walker)生殖系统和飞行系统发育的影响,对1日龄饥饿处理后粘虫的卵巢发育级别、产卵前期、飞行肌和飞行能力进行了系统研究。结果表明, 1日龄饥饿对粘虫成虫卵巢发育级别、产卵前期、中胸背纵肌干重、飞行能力等均有显著的影响。饥饿后成虫卵巢发育级别显著高于对照,产卵前期显著短于对照。成虫中胸背纵肌干重从饥饿后96 h开始下降,至120 h时饥饿粘虫(5.1 mg)显著低于对照(5.86 mg)。成虫飞行能力从饥饿后96 h开始显著低于对照,此时饥饿处理粘虫蛾的飞行距离平均为22.03 km,飞行时间平均为4.07 h,显著低于同时期的对照粘虫的飞行距离(42.3 km)和飞行时间(7.99 h),尽管在饥饿后72 h内差异不显著。实验结果显示,1日龄饥饿可以显著抑制粘虫飞行系统的发育,加速飞行向生殖的转变。     

Nutrient limitation results in juvenile hormone-mediated resorption of previtellogenic ovarian follicles in mosquitoes

Juvenile hormone (JH) is a central hormonal regulator of previtellogenic development in female Aedes aegypti mosquitoes. JH levels are low at eclosion and increase during the first day after adult emergence. This initial rise in JH is essential for female reproductive maturation. After previtellogenic maturation is complete, the mosquito enters a ‘state-of-arrest’ during which JH synthesis continues at a slower pace and further ovary development is repressed until a blood meal is taken. By examining the relationships between juvenile hormone, follicular resorption and nutrition in A. aegypti, we were able to define a critical role of JH during the previtellogenic resting stage. The rate of follicular resorption in resting stage mosquitoes is dependent on nutritional quality. Feeding water alone caused the rate of follicular resorption to reach over 20% by day 7 after emergence. Conversely, feeding a 20% sucrose solution caused resorption to remain below 5% during the entire experimental period. Mosquitoes fed 3% sucrose show rates of resorption intermediate between water and 20% sucrose and only reached 10% by day 7 after emergence. Follicular resorption is related to JH levels. Ligated abdomens separated from a source of JH (the corpora allata) showed an increase in resorption comparable to similarly aged starved mosquitoes (16%). Resorption in ligated abdomens was reduced to 6% by application of methoprene. The application of methoprene was also sufficient to prevent resorption in intact mosquitoes starved for 48 h (14% starved vs. 4% starved with methoprene). Additionally, active caspases were localized to resorbing follicles indicating that an apoptotic cell-death mechanism is responsible for follicular resorption during the previtellogenic resting stage. Taken together, these results indicate that JH mediates reproductive trade-offs in resting stage mosquitoes in response to nutrition.     

Insulin/IGF signaling regulates the change in commitment in imaginal discs and primordia by overriding the effect of juvenile hormone

At the beginning of the final larval (fifth) instar of Manduca sexta, imaginal precursors including wing discs and eye primordia initiate metamorphic changes, such as pupal commitment, patterning and cell proliferation. Juvenile hormone (JH) prevents these changes in earlier instars and in starved final instar larvae, but nutrient intake overcomes this effect of JH in the latter. In this study, we show that a molecular marker of pupal commitment, broad, is up-regulated in the wing discs by feeding on sucrose or by bovine insulin or Manduca bombyxin in starved final instar larvae. This effect of insulin could not be prevented by JH. In vitro insulin had no effect on broad expression but relieved the suppression of broad expression by JH. This effect of insulin was directly on the disc as shown by its reduction in the presence of insulin receptor dsRNA. In starved penultimate fourth instar larvae, broad expression in the wing disc was not up-regulated by insulin. The discs became responsive to this action of insulin during the molt to the fifth instar together with the ability to become pupally committed in response to 20-hydroxyecdysone. Thus, the Manduca bombyxin acts as a metamorphosis-initiating factor in the imaginal precursors.     

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.