Ecdysteroids and adult diapause in the Colorado potato beetle, Leptinotarsa decemlineata

ABSTRACT. The difference in ecdysteroid activity in short-day (10-h photo-phase) and long-day (16-h photophase) Leptinotarsa decemlineata Say adults was characterized by high performance liquid chromatography, which revealed that for short-day beetles ecdysterone and ecdysone are the major constituents of the free ecdysteroids, whereas in long-day beetles products co-migrating with 2-deoxyecdysone and 2-deoxyecdysterone are just as abundant. Ecdysteroids were detected (15 ng/ml) only in the haemolymph of females. Ligation experiments showed that the induction of the diapause syndrome by inactivation of the corpora allata or the brain not only resulted in the formation of the typical diapause proteins but also in an increase of the ecdysteroid activity. It is suggested that adult diapause in L.decemlineata is regulated by a multifactorial system.     

Juvenile hormone and the control of adult diapause in the Colorado potato beetle,Leptinotarsa decemlineata

One of the major hormonal events preceding environmentally controlled diapause in the Colorado potato beetle, Leptinotarsa decemlineata, is the inhibition of the corpora allata. This paper reviews briefly the data developed by our laboratory on the role of the neuroendocrine system in the control of the corpus allatum. In addition, we demonstrate that during transport in the hemolymph JH is bound to a JH-III specific binding protein. The JH-binding sites of this protein have a high affinity for JH-III and display stereoselectivity. New data are presented showing that, in beetle hemolymph, JH-III specific binding occurs with the lipophorin fraction.     

Thirty-five years of diapause research with the Colorado potato beetle

An ever increasing biological knowledge will make us better and better equipped for manipulating biological processes and for warning us in time against possible dangers which an unguided technology can bring to man and its biotic environment' (de Wilde, 1982).     

Juvenile hormone-induced break and termination of diapause in the Colorado potato beetle

Topical applications of Cecropia juvenile hormone I (JH) and several analogues, 1 day after the initiation of diapause, induce a break in diapause 8 to 10 days later, characterized by emergence from the soil, feeding, mating, and reproduction. Activation is only temporary when beetles are kept in short-day photoperiods. The percentage of beetles activated and the duration of activation depend on the nature of the JH and the dose applied. JH application during prediapause only postpones diapause, whereas beetles which have spent 2 months in diapause are activated rather easily. Diapause is completely terminated when JH application is accompanied by a transfer of the beetles to long-day conditions. Thirty μg JH applied to allatectomized females in long-day conditions allows them to reproduce for over 50 days.The extent to which the endocrine system is involved in activation has been investigated. Allatectomy does not change JH-induced activation at long or short daylengths. Volumetric measurements indicate that the corpora allata remain inactive as long as measurable amounts of JH circulate in the blood. An increase in corpus allatum activity after day 8 further stimulates long-day oviposition. Gomoripositive neurosecretory cells in the brain are activated by JH within 1 day. The hypothesis is advanced that a JH-induced break or termination of diapause is mediated through the neuroendocrine system.     

Plant volatiles moderate response to aggregation pheromone in Colorado potato beetle

Abstract:  The orientation of the Colorado potato beetle, Leptinotarsa decemlineata , to a male-produced aggregation pheromone, ( S )-3,7-dimethyl-2-oxo-oct-6-ene-1,3-diol, a three-component plant attractant blend [comprised of ( Z )-3-hexenyl acetate + (±)-linalool + methyl salicylate], and other potato volatiles (nonanal and 2-phenylethanol) were tested. All compounds were previously shown to be active in coupled gas chromatography/electroantennogram experiments. Both the three-component plant attractant blend and 2-phenylethanol were attractive to adult beetles. While male beetles oriented preferentially to both plant attractants vs. a control, females showed little preference. Combining the plant attractants with the pheromone resulted in sexually dimorphic responses similar to those seen with either plant attractant alone. Addition of nonanal abolished the sexually dimorphic response to the pheromone + 2-phenylethanol blend; the new three-component blend was attractive to both sexes. In both laboratory bioassays and field experiments, a combination of the pheromone + the three-component plant attractant was preferred over the plant attractant alone. Thus, it seems likely that combinations of pheromone + plant volatiles may be the most efficacious for field use.     

Differential regulation of HSC70, HSP70, HSP90 alpha, and HSP90 beta mRNA expression by mitogen activation and heat shock in human lymphocytes

A subset of heat shock proteins, HSP90 alpha, HSP90 beta, and a member of the HSP70 family, HSC70, shows enhanced synthesis following mitogenic activation as well as heat shock in human peripheral blood mononuclear cells. In this study, we have examined expression of mRNA for these proteins, including the major 70-kDa heat shock protein, HSP70, in mononuclear cells following either heat shock or mitogenic activation with phytohemagglutinin (PHA), ionomycin, and the phorbol ester, tetradecanoyl phorbol acetate. The results demonstrate that the kinetics of mRNA expression of these four genes generally parallel the kinetics of enhanced protein synthesis seen following either heat shock or mitogen activation and provide clear evidence that mitogen-induced synthesis of HSC70 and HSP90 is due to increased mRNA levels and not simply to enhanced translation of preexisting mRNA. Although most previous studies have focused on cell cycle regulation of HSP70 mRNA, we found that HSP70 mRNA was only slightly and transiently induced by PHA activation, while HSC70 is the predominant 70-kDa heat shock protein homologue induced by mitogens. Similarly, HSP90 alpha appears more inducible by heat shock than mitogens while the opposite is true for HSP90 beta. These results suggest that, although HSP70 and HSC70 have been shown to contain similar promoter regions, additional regulatory mechanisms which result in differential expression to a given stimulus must exist. They clearly demonstrate that human lymphocytes are an important model system for determining mechanisms for regulation of heat shock protein synthesis in unstressed cells. Finally, based on kinetics of mRNA expression, the results are consistent with the hypothesis that HSC70 and HSP90 gene expression are driven by an IL-2/IL-2 receptor-dependent pathway in human T cells.     

Monitoring diapause development in the Colorado potato beetle, Leptinotarsa decemlineata, under field conditions using molecular biomarkers

A multiplex PCR protocol was developed using five diapause-regulated genes to monitor diapause development of the Colorado potato beetle under field conditions. A total of 870 beetles from the Red River valley of North Dakota and Minnesota, USA, were screened for three consecutive years. Out of the 32 possible expression profiles, eight could be arranged in chronological order of diapause development. These eight profiles account for over 92% of the beetles surveyed. Intra-population variation in diapause phenotypes was observed in the field. Some beetles were already in the diapause initiation phase in June when the day length was greater than 17 h. Inter-seasonal variation in the timing of diapause development was also noted. The greatest differences were before the day length decreased to less than 15 h. Anomalies in the results, e.g., the presence of the diapause maintenance phase profiles in beetles collected on the potato plants, argue that laboratory results are not always equivalent with what is observed under field conditions.     

Evidence of controlled corpus allatum activity in the adult Colorado potato beetle

The in vivo control of corpus allatum (CA) activity in females of Leptinotarsa decemlineata was investigated. Evidence was obtained that CA activity is adjusted by negative feedback when juvenile hormone (JH) titres are changed experimentally. Conclusions are based on determination of the rate of in vitro JH synthesis by the CA, on changes in CA volume, and on JH titres in the haemolymph. These assay methods are used alternatively in some of the experiments.After unilateral allatectomy, the remaining CA had doubled its activity 7 days later. On the other hand, the activity of CA in young adults was suppressed after the JH titre was elevated by the implantations of 2 CA taken from active females. Similarly, in beetles treated topically with exogenous JH the CA atrophied and showed a much reduced activity after 5 days. Denervation of CA in 0-day-old long-day and 7-day-old short-day females did not change CA activity when measured 1 day later.     

Differential expression of two types of sucrose synthase-encoding genes in wheat in response to anaerobiosis, cold shock and light

The expression of two types of sucrose synthase-encoding genes, Ss1 and Ss2, in hexaploid wheat (Triticum aestivum, L.), has been investigated using type-specific probes, corresponding to the 250-270 bp C-terminal portions of the respective cDNA clones. Both types of genes are highly expressed in developing endosperm, where the expression of the Ss2 type slightly precedes in time that of the Ss1 type. Expression of Ss genes is lower in etiolated leaves and in roots than in endosperm. In the first two tissues, the Ss1 mRNA is much more abundant than the Ss2 mRNA, and the Ss1 mRNA level sharply increases in response to anaerobiosis and to cold shock (6 degrees C), while the level of Ss2 mRNA is not significantly affected. Upon illumination of etiolated leaves, the Ss1 level mRNA decreases significantly and the Ss2 mRNA level increases.     

Differential gene expression of HSC70/HSP70 in yellowtail cells in response to chaperone-mediated autophagy

A cell line derived from the tailfin of the marine teleost yellowtail fish Seriola quinqueradiata was established to examine cellular temperature regulation in an ectothermic animal. Three cytosolic members of the HSP70 family, heat-shock cognate proteins HSC70-1, HSC70-2 and heat-shock protein HSP70, were isolated from cultured yellowtail cells as stress-responsive biomarkers. Expression of hsp70 was heat-inducible, in contrast to the hsc70-1 gene product, which was expressed constitutively. In addition, expression of hsc70-2 was only induced under severe heat-shock conditions. Subcellular fractionation and immunocytochemistry showed localization of HSC70/HSP70 in the lysosomes, indicating that chaperone-mediated autophagy is induced by heat shock. Thus, chaperone-mediated autophagy is assisted by HSC70/HSP70, and heat-inducible expression of the genes encoding these proteins may be responsible for survival and adaptation under heat-shock conditions in fish cells.     

Quiescence in the Colorado potato beetle, Leptinotarsa decemlineata

Quiescence (death feigning) was induced in the Colorado potato beetle, Leptinotarsa decemlineata by mechanical disturbance of live and artificial plants on which beetles were walking, feeding or grooming. The response consisted of a sudden cessation of activity lasting 12 to 500 s. Recovery from this immobile state was usually preceded by either antennal or leg movement. The time taken for beetles to come out of the immobile state (i.e. recovery time) was not dependent on age or sex of beetles or on stimulus duration, but was dependent on degree of displacement and on satiation level. Repeated stimulations led to longer recovery times and to a smaller proportion of responding beetles. Stimulation within the immobile state also prolonged recovery time. The most effective frequency of mechanical disturbance for startling beetles was 30 Hz. This response is presumed to be part of the extensive defense repertoire of this beetle, but we have so far been unable to discover a natural enemy that will elicit it.     

Photosynthetic responses of potato to Colorado potato beetle injury and differences in injury between adult males and females

Establishing rates of injury to plants and the physiological impact of this injury provides essential data in the development of economic injury levels, but variation of sex effects is not often considered. Here, we examined injury by the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), larvae and adult males and females on potato, Solanum tuberosum L. (Solanaceae). Specifically, we looked for adult sex differences between males and females in injury rates (= leaf consumption rates), and examined the impact of all types of injury (larval, adult male, and adult female) on gas exchange parameters of remaining potato leaf tissue. Experiments were conducted in the field and in growth chambers on Frito‐Lay proprietary and Pike chipping‐potato varieties at pre‐blooming and blooming stages. We found no change in photosynthetic rates on remaining (uninjured) leaf tissue infested with male, female, or fourth‐stage larva of Colorado potato beetle. However, when the midrib was cut in trials with male beetles, the remaining tissue above the injury exhibited photosynthetic rate reductions as a result of stomatal limitations. These findings are consistent with the pattern that we and other researchers have observed with gross tissue removal by various insects on other plant species. Adult females consumed more tissue than males, and temperature was positively correlated with feeding rates for both sexes. Sex‐related differences in feeding rate are most important to studies quantifying consumption rates for economically important species because of its potential impact on resulting economic injury level calculations.     

Lack of an HSP70 heat shock response in two Antarctic marine invertebrates

Members of the HSP70 gene family comprising the inducible (HSP70) genes and GRP78 (glucose-regulated protein 78 kDa) were identified in an Antarctic sea star (Odontaster validus) and an Antarctic gammarid (Paraceradocus gibber). These genes were surveyed for expression levels via Q-PCR after an acute 2-hour heat shock experiment in both animals and a time course assay in O. validus. No significant up-regulation was detected for any of the genes in either of the animals during the acute heat shock. The time course experiment in O. validus produced slightly different results with an initial down regulation in these genes at 2°C, but no significant up-regulation of the genes either at 2 or 6°C. Therefore, the classical heat shock response is absent in both species. The data is discussed in the context of the organisms’ thermal tolerance and the applicability of HSP70 to monitor thermal stress in Antarctic marine organisms.     

Effect of photoperiod and allatectomy on reproduction and (second) diapause induction in post-diapause adult females of the Colorado potato beetle,Leptinotarsa decemlineata Say

Summary

The effect of photoperiod and allatectomy on the rates of oviposition and juvenile hormone (JH) synthesis was studied in female beetles after the break of adult diapause. The results indicate that after diapause, photoperiod has no effect on oviposition rates. However, the photoperiodic effect on diapause induction is restored within a few days after the break of the first diapause. Allatectomy performed within one day after diapause did not induce a second diapause, whereas about 40% of the beetles allatectomized after 3 or more days responded by entering a second diapause. Oogenesis in the operated animals was never completely prevented under long and short day conditions. These preliminary results suggest a change in the sensitivity of post-diapause beetles to photoperiodic and endocrine manipulation as compared with pre-diapause insects.