Transport and kinetics of diflubenzuron and pyriproxyfen in the beet armywormSpodoptera exigua and its predatorPodisus maculiventris

Transport and retention of the insect growth regulators (IGRs) diflubenzuron and pyriproxyfen in larvae of the beet armywormSpodoptera exigua (Hübner) and in nymphs of the predatory bugPodisus maculiventris (Say) were investigated. In a first experiment, the retention of orally administered [¹⁴C]radiolabeled isotopes of both compounds in fifth-instar larvae of the beet armyworm was studied. Rate of excretion of both IGRs inS. exigua caterpillars was high, with a 50% excretion time of approximately 6 h after intake. In a second experiment, the transport of the compounds from prey to predator and their retention inside the predator were studied. Fifthinstar nymphs ofP. maculiventris were allowed to feed on caterpillars that had been given contaminated food. For both diflubenzuron and pyriproxyfen, more than 80% of the amount of radiolabel applied was recovered in consumed prey. Low levels of radioactivity (c. 3% of the applied amount of radiolabel) were also found in the fluid regurgitated by the prey larvae when attacked by the predatory bugs. Relatively small amounts of radiolabel (c. 8 and 15% of the amount orally applied to the prey for diflubenzuron and pyriproxyfen, respectively) were ingested byP. maculiventris nymphs when feeding on beet armyworm caterpillars. The data suggest that the predators did not use gut content as food. The pattern of excretion in nymphs ofP. maculiventris differed between compounds. For diflubenzuron, there was a drastic decrease of radioactivity inside the predator body of around 40% within the first 6 h and then the level of retained radiolabel remained stable at 3–4% up to 72 h. For pyriproxyfen, a slow decrease of radioactivity inside the body was observed and at 72 h only 2% of the applied quantity was detected. Results of this study are discussed in relation to the findings from previous studies on the toxicity of both IGRs toP. maculiventris.     

Physiological effects of a juvenile hormone analog on larvae of Spodoptera littoralis

Topical application of JHA to Spodoptera littoralis larvae extends the duration and increases the final weight of the last larval instar. No supernumary moults occur. Respiration decreases to very low levels and glycogen and lipid stores increase. Respiration remains lower in JHA-treated pharate pupae and more polyunsaturated C₁₈ fatty acids accumulate than in normal pharate pupae. These physiological parameters are similar to those occurring during diapause but are not definitive. Diapause has not been reported in field populations of S. littoralis, nor it's artificial induction by photoperiodic manipulation.

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Résumé Le dernier stade des chenilles de Spodoptera littoralis, traitées avec JHA, est nettement prolongé par rapport aux témoins. Bien que le poids final des chenilles traitées soit plus élevé que celui des témoins, il n'y a pas de mue surnuméraire. Ces chenilles géantes s'alimentent rarement et leur respiration est sérieusement réduite. Les réserves de glycogène s'accumulent chez les chenilles traitées à la même date chronologique que chez les prénymphes non traitées. Bien que les prénymphes traitées à la JHA conservent leur profil biochimique juvénile — tout au moins dans la mesure où on considère la teneur en glycogène et en lipides totales — leur composition en acides gras saturés et non saturés diffère de celle normalement rencontrée à la fin du développement larvaire, et beaucoup plus d'acide oléique monosaturé s'accumule finalement chez les insectes traités par JHA. Ces résultats suggèrent que la JHA fournie peut avoir provoqué un état de développement de diapause naissante semblable par quelques traits fondamentaux à celle induite par la JH endogène chez les insectes enclins à la diapause. Il est cependant prématuré de définir cet état physiologique comme indiquant une vraie diapause chez Spodoptera littoralis.

     

Effects of a juvenile hormone analog, pyriproxyfen, on the apterous form of Lipaphis erysimi

Effects of a juvenile hormone analog, pyriproxyfen, on various developmental stadia of the apterous form of the turnip aphid, Lipaphis erysimi (Kaltenbach), were bioassayed at three concentrations (50, 100, and 150 mg [AI]/l) in the laboratory. Supernumerary-molted nymphs with 1-3 extra molts were found when the first three nymphal instars were treated, and all these nymphs died prematurely. In contrast, all treated fourth instar nymphs molted normally to adults. The longevity of all pyriproxyfen-treated L. erysimi nymphs and adults and the fecundity of treated adults were reduced by 50%. Higher concentrations of pyriproxyfen (100 and 150 mg [AI]/l) caused sterility in adults from treated fourth instars; whereas the lowest concentration (50 mg [AI]/l) did not cause any adult sterility. A majority of adults from treated fourth instars and treated adults produced normal nymphs, and some adults produced dead nymphs with normal appendages or dead and deformed nymphs without any appendages. Normal nymphs produced by the adults from treated adults or treated at fourth instars developed more slowly from first instar to adult than the water-treated nymphs, and all adults in the new generation apparently reproduced normally. The potential role of pyriproxyfen in a vegetable aphid IPM program was discussed.     

The role of juvenile hormone esterase in terminating larval feeding and initiating metamorphic development in Trichoplusia ni

This study shows, first, that when JH degradation by JHE is blocked with an inhibitor (EPPAT, O-ethyl-S-phenyl-phosphoramidothiolate), prothoracicotropic/ecdysone release/effects are postponed in the cabbage looper Trichoplusia ni (Hübner) (Noctuidae). Thus, JHE is an important component of JH degradation, implying that without normal degradation the JH titer will become abnormally high. Second, this accumulation of endogenous JH in EPPAT treated larvae results in an extra larval molt. Therefore, JHE is also important in the control of the nature of the molt, by controlling the JH titer. Third, this study demonstrates that EPPAT at proper doses is a viable probe for studying enzyme and hormone action in vivo without pharmacological artifacts.

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Résumé Cette étude indique d'abord que, lorsque la dégradation de l'hormone juvénile (JH) par la JHE est bloquée par un inhibiteur (EPPAT, O-éthyl-S-phényl-phosphoramidothiolate) les effets prothoracicotropiques—libération d'ecdysone—sont retardés chez Trichoplusia ni Hübner. Ainsi, la JHE est un élément important de la dégradation de JH, impliquant que sans une dégradation régulière, la teneur en JH deviendra anormalement élevée. Cette accumulation d'hormone juvénile endogène chez les larves traitées à l'EPPAT provoque de plus une mue larvaire supplémentaire. Par conséquent, JHE est importante aussi dans le contrôle de la nature de la mue, en déterminant la teneur en JH. Enfin, cette étude a montré que l'EPPAT à des doses appropriées est un moyen efficace pur étudier l'action hormonale in vivo sans artéfacts pharmaceutiques.

     

保幼激素类似物对斜纹夜蛾核型多角体病毒在宿主血淋巴中增殖动态的影响

通过研究保幼激素类似物(juvenile hormone analogues, JHA) methoprene对斜纹夜蛾核型多角体病毒（Spodoptera litura nucleopolyhedrovirus, SpltNPV）在宿主血淋巴中增殖的影响,以探明JHA促进 SpltNPV增殖的初步机制,为阐明JHA促进病毒增殖提供更全面的理论依据。应用SDS PAGE及Western blot法,分析了methoprene对SpltNPV多角体蛋白(polyhedron, POLH)在宿主斜纹夜蛾6龄幼虫血淋巴中合成的影响。结果表明：经methoprene处理后2～3天可明显促进幼虫血淋巴液中POLH的合成。在此基础上,通过荧光定量PCR检测,发现methoprene对SpltNPV在幼虫血淋巴液复制的影响主要发生在处理后的第4和第5天,该期间polh基因的拷贝数比对照显著增加,拷贝数的峰值达1.22×10¹⁰/mL。     

Effects of a juvenile hormone analogue on the eggs, post-embryonic development, metamorphosis and diapause induction of the Colorado potato beetle, Leptinotarsa decemlineata

The effect of a juvenile hormone analogue, S-71639, was tested on the eggs, four larval instars and adults of the Colorado potato beetle, Leptinotarsa decemlineata Say, by topical application or after treatment of the foodplant. The last larval instar is very sensitive to S-71639. Treatment of this instar delayed the onset of pupation and prevented adult emergence. Treated animals showed severe abnormalities, but they were not immediately killed at the doses used in this study. Treatment of larvae also interfered with the photoperiodic induction of diapause. Adults, kept under diapausing conditions, started to lay eggs after treatment with S-71639. The ovicidal effect of the compound was rather weak. The implications for practical use of S-71639 in control of the Colorado potato beetle are being discussed.

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Résumé L'effet d'un analogue de l'hormone juvénile, S-71639, a été testé sur les oeufs, les quatre stades larvaires et les adultes du doryphore, Leptinotarsa decemlineata Say, par application topique ou après traitement de la plante-hôte. Le dernier stade larvaire est très sensible au S-71639. Le traitement de ce stade retarde le début de la métamorphose et empêche l'émergence adulte. Les animaux traités montrent de graves anomalies, mais ne sont pas immédiatement tués par les doses utilisées dans cette étude. Le traitement des larves perturbe aussi l'induction photopériodique de la diapause. Les adultes placés dans des conditions de diapause, commencent à pondre après traitement au S-71639. L'effet ovicide de la substance est plutôt faible. Les implications pour l'utilisation pratique du S-71639 dans la lutte contre le doryphore sont discutées.

     

Effects of pyriproxyfen on ovarian development and fecundity ofRhagoletis pomonella flies

Three-day old female apple maggot flies,Rhagoletis pomonella (Walsh), were topically exposed to different doses (0.1, 1, 10, and 100 μg per fly) of a juvenile hormone mimic, pyriproxyfen, in the laboratory. Pyriproxyfen had little lethal effect on females except at the extremely high dose of 100 μg. It also had no significant effect on egg viability of treated females. A non-lethal dose of 1 μg per fly did, however, enhance significantly the fecundity (egg production) as well as the ovarian development (number of eggs in ovaries and length of egg folicles) of treated flies. We conclude that pyriproxyfen could be a useful aid in exploring endocrine regulation of feeding and reproductive physiology behavior inR. pomonella, about which current knowledge is scant.     

The onset of metamorphosis in Tenebrio molitor L.: Effects of a juvenile hormone analogue and of 20-hydroxyecdysone

Sensitivity to juvenile hormone and to 20-hydroxyecdysone has been investigated during the last-larval stages of Tenebrio molitor. Topical applications of a juvenile hormone analogue (K-421d) showed that the sensitive period, occurring before apolysis, is relatively short (less than 4 days in a 3-week instar) and divided into two phases. Treatment during the first and longest phase induced a delay in development and then an increase in larval moult percentage. Treatment during the second phase induced several abnormal moults (prothetelic larvae and larval-pupal intermediates).Injections of massive doses of 20-hydroxyecdysone (10 μg per animal) also evidenced a period of disturbance of the morphogenetic programme, beginning before pupal apolysis but continuing several days after.Comparison of the sensitive periods to both hormones suggests that a very important and rapid step of the larval-pupal programme change is controlled hormonally just before pupal apolysis.     

The effects of ingested ecdysteroid agonists (20-hydroxyecdysone, RH5849 and RH5992) and an ecdysteroid antagonist (cucurbitacin B) on larval development of two polyphagous lepidopterans (Acherontia atropos and Lacanobia oleracea)

Larvae of two polyphagous lepidopteran species, Lacanobia oleracea (Tomato moth) and Acherontia atropos (Death's head hawkmoth), have been treated with representatives of three classes of compounds which are known to interact with the ligand binding site of insect steroid hormone receptors: a steroidal ecdysteroid (20-hydroxyecdysone; 20E; agonist), two non-steroidal dibenzoylhydrazines (RH5849 and RH5992; agonists) and the triterpenoid cucurbitacin B (cucB; antagonist). Both species are unaffected by dietary 20E at concentrations up to 400 ppm. L. oleracea metabolises ingested [³H]20E to a mixture of C-22 fatty acyl esters, while A. atropos excretes [³H]20E unmetabolised. Both species are susceptible to the dibenzoylhydrazines when these are incorporated into the diet, with RH5992 proving lethal at 1 ppm and RH5849 proving lethal at 10 ppm. Thus, the metabolic/excretion mechanisms which are so effective against ingested 20E do not recognise the non-steroidal agonists. The two species showed varying degrees of tolerance to cucB; L. oleracea was unaffected by 400 ppm in the diet, while A. atropos showed effects at 400 ppm, but not at 40 ppm. Feeding cucB in conjunction with 20E or injecting cucB when the ecdysteroid titre was low or rising also had no effect in L. oleracea. It is suggested that tolerance to the two classes of natural products (ecdysteroids and cucurbitacins) is associated with the occurrence of these compounds in some of the host plants of these species; evidence is presented for the presence of phytoecdysteroids in the host plants.     

Competition between wild-type and a marked recombinant baculovirus (Spodoptera exigua nucleopolyhedrovirus) with enhanced speed of action in insect larvae

Competition between virus genotypes in insect hosts is a key element of virus fitness, affecting their long-term persistence in agro-ecosystems. Little information is available on virus competition in insect hosts or during serial passages from one cohort of hosts to the next. Here we report on the competition between two genotypes of Spodoptera exigua nucleopolyhedrovirus (SeMNPV), when serially passaged as mixtures in cohorts of 4th instar S. exigua larvae. One of the genotypes was a SeMNPV wild-type isolate, SeUS1, while the other was a SeMNPV recombinant (SeMNPV-XD1) having a greater speed of kill than SeUS1. SeXD1 lacks a suite of genes, including the ecdysteroid UDP-glucosyl transferase (egt) gene. SeXD1 expresses the green fluorescent protein (GFP) gene, enabling the identification of SeXD1 in cell culture and in insects. The relative proportion of SeUS1 and SeXD1 in successive passages of mixed infections in various ratios was determined by plaque assays of budded virus from infected larvae and by polymerase chain reactions and restriction enzyme analyses. The SeUS1 genotype outcompeted recombinant SeXD1 over successive passages. Depending on the initial virus genotype ratio, the recombinant SeXD1 was no longer detected after 6-12 passages. A mathematical model was developed to characterize the competition dynamics. Overall, the ratio SeUS1/XD1 increased by a factor 1.9 per passage. The findings suggest that under the experimental conditions recombinant SeXD1 is displaced by the wild-type strain SeUS1, but further studies are needed to ascertain that this is also the case when the same baculoviruses would be used in agro-ecosystems.     

Persistence and Effects of Parasitic Genotypes in a Mixed Population of the Spodoptera exigua Nucleopolyhedrovirus

Spod-X, a commercialized bioinsecticide for the control of the pest Spodoptera exigua, is based on a nucleopolyhedrovirus (NPV) of S. exigua (SeMNPV) isolated in Florida (US2wt). This field isolate is made up of at least seven genotypic variants, of which two (US2C and US2E) have defective genomes and act as parasites, reducing the pathogenicity of the viral population. Upon co-infection of US2wt and a Spanish field isolate of the same virus (SP2wt), persistence of the defective variants (US2C, US2E) in the viral progeny was observed. This persistence diluted the presence of intact, self-infectious genotypes in the progeny, decreasing the pathogenicity of these viral inocula. Further passages of viral occlusion bodies produced after the co-infection revealed that the parasite US2C continued replicating and constituted up to 30% of the viral progeny in some samples. In addition, the presence of US2C within SP2wt significantly decreased the pathogenicity of contaminated inocula by 3.6-fold. The use of foreign virus field isolates containing defective genomes and their possible impact on the biological activity of native NPV populations may be a cause for concern where these viruses are used as agents for biological control.     

Effect of juvenile hormone on caste determination and colony processes in the bumblebee Bombus terrestris

To investigate the role of juvenile hormone (JH) in caste determination, first and second instar larvae of Bombus terrestris were topically treated with one of three doses (2, 10, or 20 g/larva) of JH dissolved in acetone. Treated larvae belonged to very young colonies that had just been started by their queen. Therefore, all larvae were supposedly destined to develop into workers. Our study demonstrates that a single application of JH in the first or second instar can lead to the development of queens and that this effect is dose- and instar-dependent. The brood (second, or third brood of the colony) to which the larvae belonged also had an effect. A clear size dimorphism of the female castes exists in B. terrestris. In this study, however, intermediates also developed from treated larvae. In fact, even untreated larvae in a treated colony developed into queens and intermediates, depending on the total dose of JH applied to the colony. There are no indications that a larva, once determined to become a queen, can be forced to become a worker by means of malnutrition. Treatment with JH also had an influence on colony processes. For instance, the appearance of queen larvae resulted in the advanced start of reproduction by workers and egg robbery, the so called competition point. This indicates again the close relationship between queen rearing and the queen-worker conflict. However, the ultimate function of this casual connection is still unclear. Further, the queen reacted to the treatment by switching to the laying of haploid eggs at an earlier date in the colony development compared to untreated colonies.     

Effects of the juvenile hormone mimic pyriproxyfen on female reproduction and longevity in the butterfly Bicyclus anynana

Female Bicyclus anynana butterflies given pyriproxyfen, a mimic of juvenile hormone, exhibited increased egg‐laying rates and early fecundity, but reduced longevity compared with control animals. Thus, pyriproxyfen application yielded antagonistic effects on different components of fitness, possibly demonstrating a juvenile hormone‐mediated trade‐off between present and future reproduction. Lifetime fecundity and egg size, however, showed no consistent response to pyriproxyfen, with lifetime fecundity being increased or decreased and egg size being reduced in one out of four experiments only. Females were most sensitive to pyriproxyfen around the onset of oviposition, coinciding with naturally increasing juvenile hormone titers in other Lepidoptera. Amounts between 1 and 10 µg pyriproxyfen were found to be effective, with, however, pronounced differences among experiments. This is attributed to differences in assay conditions. High pyriproxyfen concentrations (100 µg) as well as repeated applications of smaller amounts did not affect reproductive traits, but tended to reduce longevity.     

The source and action of head factors regulating juvenile hormone esterase in larvae of the cabbage looper, Trichoplusia ni

Brain (median or lateral regions) or suboesophageal ganglion (SOG) homogenates of Day 1 fifth instar larvae of Trichoplusia ni induced the appearance of haemolymph juvenile hormone esterase (JHE) when injected into Day 1, Day 2 or early Day 4 fifth instar ligated hosts. Brain and SOG homogenates of late fourth instars also induced JHE when injected into Day 1 hosts, whole late fifth instar and pupal tissue did not. The pattern of JHE induction by early fourth through Day 3 fifth instar brain and SOG homogenates correlated with natural haemolymph JHE activity occurring at these times. Implantation of late fourth and Day 1 fifth instar brains and/or SOG into similar age hosts similarly induced JHE activity while prothoracic and abdominal ganglia did not. The relative levels of induction following implantation were SOG<brain<brain+SOG. JHE activity which appears in the haemolymph following injection of brain homogenates appears to be largely due to a single enzyme which has an isoelectric point indistinguishable from that of the natural haemolymph enzyme. Evidence is presented which suggests that inhibitory as well as stimulatory brain factors are involved in JHE regulation.     

Effect of juvenile hormone on the embryogenesis of a polyembryonic wasp,copidosoma floridanum,in vitro

Summary Single two-cell-stage embryos of a polyembryonic waspCopidosoma floridanum cultured in 20 μl droplets of culture medium developed to morulae at the same developmental rate as those in host eggs, but the subsequent development into polymorulae was inferior. This inferior development was markedly improved by addition of juvenile hormone (I, II, or III) or its analogues to the culture medium in a concentration-dependent manner.     

Effects of a juvenile hormone analogue on the duration of the fifth instar in the milkweed bug Oncopeltus fasciatus

Topical application of JHA to fifth instar nymphs of Oncopeltus fasciatus, immediately following ecdysis from the fourth instar, decreases the duration of the fifth instar by approximately 36 hr in addition to inducing a supernumerary larval moult. JHA appears to accelerate the time of subsequent ecdysis in two ways: first, the onset of ecdysone secretion is accelerated, and is accompanied by a similarly premature initiation of mitotic activity in epidermal cells. This is the classical prothoracicotropic action of JH. Second, the period between the onset of mitotic activity and the time of ecdysis itself is shortened. That is, once cellular activities associated with the moulting cycle are triggered by ecdysone, such activities are completed more rapidly in the presence of JHA. It appears that the larval-larval moult induced by JHA requires intrinsically less time to accomplish than a normal metamorphic moult.     

Relationship of flight and reproduction in beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), a migrant lacking the oogenesis-flight syndrome

The beet armyworm, Spodoptera exigua, undertakes long-distance migration. We used flight mills to investigate the interaction between flight and reproduction in this species given the apparent absence of the oogenesis-flight syndrome. This syndrome, common in many migratory insects, is characterized by a suite of traits including migration during the pre-oviposition period followed by a switch to oogenesis. No negative effects of inter-ovipositional flight on lifetime fecundity were observed. Instead, adult reproductive output suffered when female flight was initiated the first day after eclosion and before oviposition, suggesting that migratory flight overlaps with the oviposition period rather than being confined to the pre-oviposition period. Mating status of both females and males had no negative influence on their flight performance except that flight distance and flight duration of 7-day-old mated females were significantly less than in unmated females. Furthermore, the number of eggs produced and mating frequency of females less than 7 days of age were not significantly correlated with flight performance, suggesting reproductive development paralleled and was independent of migratory behavior. This independent relationship between flight and reproduction of adults is consistent with the very short pre-oviposition period in this species, and suggests that resources are partitioned between these activities during pupal development. Together, our results uncovered neither obvious trade-offs nor mutual suppression between flight and reproduction in S. exigua, which indicates the lack of an oogenesis-flight syndrome for coordination of these two energy-intensive processes. We propose a conceptual model of migration for this species based on the current and previous studies.     

The effects of mating,exogenous juvenile hormone and a juvenile hormone analogue on pheromone titre,calling and oviposition in the omnivorous leafroller moth (Platynota stultana)

Mating in Platynota stultana resulted in the termination of calling, the gradual reduction of pheromone in the pheromone glands to non-detectable levels (<0.1 ng/♀) within 14 h, and oviposition of the first batch of eggs 20–24 h after copulation. Decapitation of virgin females resulted in a similar decline in pheromone titre, and also eliminated oviposition and calling. Pheromone production appears to be controlled via the head. Mating probably terminates neural or hormonal input required for pheromone production and/or removes neural or hormonal inhibition of pheromone degradation. A juvenile hormone analogue (ZR-512) and juvenile hormones I, II and III applied exogenously to virgin females elicited oviposition comparable to mated females and terminated calling within 48 h. The juvenile hormone analogue also appeared to block pheromone production in virgin females. These results suggest that juvenile hormone may be involved in the switch from virgin to mated behaviour in this species.     

Altered juvenile hormone metabolism, reproduction and stress response in Drosophila adults with genetic ablation of the corpus allatum cells

Juvenile hormone (JH), which controls many developmental and physiological processes in Drosophila melanogaster, is synthesized de novo in the specialized endocrine glands, corpus allatum (CA). The present study concerns JH metabolism, reproduction and stress resistance in Drosophila with genetic ablation of a part of CA cells. The correlated regulation of JH biosynthesis and degradation in Drosophila adults has been found: ablation of CA cells led to (1) a dramatic decrease in activity of the key regulatory enzyme of JH biosynthesis, juvenile hormone acid methyl transferase and (2) a considerable increase in JH-hydrolyzing activity. It has been also shown that ablation of CA cells caused three significant physiological changes: (1) an increase in the intensity of response of JH degradation system to heat stress; (2) a disturbance of reproduction; (3) a decrease in stress resistance. Pharmacological rise of JH level rescued JH-hydrolyzing activity, fecundity and stress resistance in CA-ablated females. Pronouncedly, all the physiological effects caused by CA ablation were significant in females but not in males indicating a sexual dimorphism of JH physiological roles in Drosophila adults.