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.     

Effects and modes of action of citrus limonoids against Leptinotarsa decemlineata

ABSTRACT Limonin and its five derivatives were evaluated in feeding bioassays for depression effects on feeding, growth and development of the fourth stadium Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Epilimonol and limonin diosphenol were most effective in depression of feeding and growth, with ED₅₀s 10 and 8 μg/cm². At a dosage of 31.6 μg/cm², epilimonol, limonin diosphenol and limonin caused both significant feeding reduction and developmental delay, while deoxylimonol, tetrahydrolimonin and limonol were not effective. Mouth-part coating and antifeedant bioassays show that feeding inhibition at host acceptance level seems to be the primary mode of action of epilimonol and limonin diosphenol.     

Age- and diapause-related acid and alkaline phosphatase activities in the intestine and malpighian tubules of the Colorado potato beetle, Leptinotarsa decemlineata (Say)

Specific activities for soluble (s) and membrane (m)-bound acid (ACP) and alkaline phosphatases (ALP) were determined in the midgut, hindgut, and Malpighian tubules for developing, prediapausing, and diapausing adult Colorado potato beetles, Leptinotarsa decemlineata (Say). High ACP activities were found in the hindgut and Malpighian tubules while high ALP activities were found in the Malpighian tubules. Variation in both ACP and ALP activities in each tissue reflects fluctuation in protein synthesis and secretion involved with digestion, excretion, and other unknown functions. Phosphatase activities in the tissues examined show the dynamic nature of diapause in this insect. Diapausing beetles showed increases in phosphatase activity after hormone treatments. JHA treatments increased s-ACP and m-ACP activities in all tissues but 20-HE did not increase activity in any tissue. Allatotropin tended to mimic the effects of JHA treatment. The s-ALP activity was also increased in all tissues whereas m-ALP was increased in the midgut and hindgut by JHA treatment. Malpighian tubule m-ALP activity was only increased by 20-HE treatments. Allatotropin was not as effective in increasing ALP activities as it was with ACP activities.     

Effects of epilimonol and starvation on feeding and oviposition by Leptinotarsa decemlineata

Epilimonol, a limonin derivative, was tested in short and long term feeding bioassays against Colorado potato beetles, Leptinotarsa decemlineata (Say), for feeding reduction and ovipositional suppression. At dosages of 10 to 30 g/cm², epilimonol reduced feeding by 42% to 65% in short term no-choice assays. However, beetles did not strongly select untreated potato leaf discs over epilimonol-treated (10 g/cm²) ones in short term choice assays. In long term tests, epilimonol at 10 g/cm² remained effective against feeding, caused mortality, and suppressed oviposition. Starvation (>16 hours/day) also caused mortality and suppressed oviposition.

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Résumé Les effets de l'épilimonol, dérivé de la limonine, ont été observés sur l'alimentation et la ponte de L. decemlineata au cours d'expériences d'alimentation brèves ou prolongées. L'épilimonol à 10 à 30 g/cm² réduit de 42 à 65% la prise de feuillage de Solanum tuberosum lors d'expériences sans choix. Au cours d'expériences prolongées, l'épilimonol à 10 g/cm² empêche la ponte et provoque la mort des adultes. Aucune accoutumance des adultes à l'épilimonol n'est apparue quant à l'alimentation et à la ponte. La ponte commence 3 à 5 jours après des traitements à l'épilimonol de 9 et 25 jours. Le jeûne supérieur à 16/jour provoque aussi la mortalité des adultes et supprime la ponte et peut être le mécanisme initial dû à l'épilimonol. Cependant, dans des expériences brèves de choix entre des rondelles de feuilles de pommes de terre traitées à 10 g/cm² et non traitées, L. decemlineata ne choisit pas particulièrement les rondelles non traités. On peut ainsi estimer que l'épilimonol n'a que des effets mineurs ou est sans effet sur la sélection de l'hôte par L. decemlineata. La régression de la prise de nourriture pourrait être due à l'action sur les sensilles gustatives de la bouche ou de de la cavité préorale qui sont moins impliquées dans le processus de sélection de l'hôte et plus responsables de la prise de nourriture.

     

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.

     

Effect of temperature and photoperiod on diapause development in a Douglas fir seed chalcid, Megastigmus spermotrophus

Douglas fir seeds infested by diapausing larvae of a chalcid, Megastigmus spermotrophus, were transferred under different temperature and photoperiod regimes at various dates during autumn and winter. Both winter diapause and prolonged diapause were compared to the diapause patterns observed in control lots kept under natural conditions. The results showed that exposure to low temperatures in autumn and winter is required for the completion of diapause development. Median adult emergence dates and the date of transfer of larvae to 20°C were negatively correlated. The frequency of prolonged diapause of larvae transferred to 20°C decreased significantly after November. When larvae were submitted to different constant temperatures, the longer the daylength, the higher and faster the reactivation. These results suggest that chalcid larvae can perceive daylength through the seed coat. This phenomenon is probably related to the fact that most of the infested seeds falling in autumn are usually covered by a layer of leaf litter during the winter. Received: 14 June 1996 / Accepted: 24 February 1997     

The effect of larval photoperiod on pupal colour and diapause in swallowtail butterflies

ABSTRACT.

• 1 There are significant differences in the effects of larval photo-period on diapause and pupal colour among the species Papilio polyxenes Fabr., P.troilus L., Battus philenor (L.) and Eurytides marcellus (Cramer).
• 2 Diapause and pupal colour in P.polyxenes and P.troilus are strongly influenced by larval photoperiod, short photophase eliciting brown diapausing pupae. Photoperiods of 15L:9D permit the expression of the green and brown pupal colour alternatives.
• 3 Pupal colour in B.philenor and E.marcellus is not affected by larval photoperiod, but short photophase induces diapause in these species.
• 4 All species except B.philenor show an association between brown pupal colour and diapause: Emarcellus when reared on long (midsummer) photophase, P.polyxenes and P.troilus when reared on short (autumnal) photophase.
• 5 In P.polyxenes, short photophase can affect pupal colour responses directly, whether the individual enters diapause or not.
• 6 Differences among the species are related to differences in the ecology of their natural pupation sites.

     

Isolation and characterization of Locusta migratoria accessory gland myotropin I (Lom-AG-MT-I) from the brain of the Colorado potato beetle,Leptinotarsa decemlineata

A novel myotropic Colorado potato beetle peptide, active in the Locusta oviduct motility assay, was isolated from a methanolic extract of 9,000 brain complexes of adult Leptinotarsa decemlineata by means of HPLC. Its sequence is Gly-Phe-Lys-Asn-Val-Ala-Leu-Ser-Thr-Ala-Arg-Gly-Phe-NH₂. This peptide is identical to Lom-AG-MT-I, a myotropin previously isolated from the male accessory glands of Locusta migratoria, using the L. migratoria oviduct motility bioassay as a monitoring system. It strongly stimulated the frequency, amplitude, and tonus of the myogenic oviduct contractions, even at low concentrations. © 1996 Wiley-Liss, Inc.     

Biological control potential of Turkish entomopathogenic nematodes against the Colorado potato beetle,Leptinotarsa decemlineata

Three Turkish isolates of the entomopathogenic nematodes Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora were evaluated under laboratory conditions (in different temperatures and doses) for their biocontrol efficiency against last instar Leptinotarsa decemlineata. Herein, the effects of infective juveniles in aqueous suspension against L. decemlineata were evaluated. S. feltiae appeared to be the most pathogenic nematode among the tested species.     

Diet-related plasticity of the digestive proteolytic system in larvae of the Colorado potato beetle (Leptinotarsa decemlineata Say)

Quantitative and qualitative changes in digestive proteolytic activities were monitored in fourth-instar larvae of the Colorado potato beetle (Leptinotarsa decemlineata Say) subjected to three different leaf diets. Depending on the diet, the larvae exhibited variable growth rates, similar for potato (Solanum tuberosum) and eggplant (Solanum melongena) diets but lower for the tomato (Lycopersicon esculentum) diet. Interestingly, these growth rates were not associated with total protease activity in the midgut. While growth of tomato-fed insects was negligible, midgut protease activity in these insects was 1.5 and 4.2 times higher than that measured for potato- and eggplant-fed insects, respectively. As seen on gelatin-containing polyacrylamide gels, midgut extracts from insects that ingested eggplant leaves contained only a few proteinase forms, while numerous forms were observed in extracts of potato- and tomato-fed larvae. Although several forms were common to the three diets, their relative importance in the insect midgut varied. This diet-related plasticity of the digestive proteolytic system in Colorado potato beetle larvae leads one to question the potential for control approaches based on the inhibition of digestive proteases. Arch. Insect Biochem. Physiol. 36:241–250, 1997. © 1997 Wiley-Liss, Inc.     

Sperm utilization and post-copulatory female-guarding in the Colorado potato beetle, Leptinotarsa decemlineata

Crosses between white and black color morphs of the Colorado potato beetle, Leptinotarsa decemlineata Say, used as genetic markers, showed that male beetles ride and guard females to achieve the three copulations required to fill the spermatheca. Multiple matings are necessary for the females to realize their full reproductive potential. Sperm mixing occurs in the spermatheca providing partial sperm precedence. The data support the competitive mate searching theory.

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Résumé Différentes combinaisons d'accouplements entre des mutants noirs et blancs du doryphore de la pomme de terre, Leptinotarsa decemlineata, servirent à étudier le comportement de guarde de la femelle par le mâle après un premier accouplement. Les résultats indiquent que le sperme de deux mâles accouplant la même femelle se mélange dans la spermathèque assurant ainsi un certain niveau de précédence du sperme du dernier mâle.La masse de sperme dans la spermathèque était inférieure à sa capacité chez les femelles ayant été accouplées une ou deux fois. Le doryphore mâle aurait donc avantage à demeurer sur la femelle après un premier accouplement afin d'obtenir le minimum de trois accouplements requis pour remplir la spermathèque avant que les autres mâles puissent accoupler cette femelle. Les autres mâles ont avantage à essayer de dérober cette femelle pour remplir eux mêmes la spermathèque ou tout au moins profiter d'une certaine précédence du sperme du dernier mâle pour fertiliser une partie des oeufs.Sans accouplements multiples, la femelle ne possède pas suffisamment de sperme pour féconder tous ses oeufs. II semble aussi que les accouplements répétés puissent augmenter sa fécondité.Les résultats supportent une stratégie reproductive de compétition plutôt qu'une simple maximisation du nombre d'accouplements.

     

Effects of photoperiod and temperature on the development and diapause of the bark beetle Ips typographus

Abstract:  Diapause was induced in a Central European population of Ips typographus grown at 20°C when the day length decreased below 16 h [50% diapause incidence occurred in the 14.7:9.3 h L:D (light:dark) regime]. The non-diapausing adults fed on days 2–6 and 10–14 after the ecdysis and swarmed after the second feeding bout with chorionated eggs in the ovaries and sperm in the spermiducts. Neither gonads nor the flight muscles matured and no swarming occurred in the diapausing adults. The development from egg to adult took about 34 days in both 18:6 h (no diapause) and 12:12 h L:D (diapause) regimes, but it was extended by up to 30% without diapause induction when only larvae or pupae were exposed to L:D 12:12 h. Diapause was induced in insects reared at L:D 12:12 h through the last larval and the pupal instars and/or in the adult stage. Temperature ≥ 23°C prevented diapause induction at L:D 12:12 h but diapause occurred at L:D 14:10 h associated with 26:6°C thermoperiod. The effect of thermoperiods on the developmental rate requires further research. Exposure of the non-diapausing adults to 5°C for several days blocked feeding and evoked a diapause-like state, whereas diapausing adults fed and their gonads slowly developed at this temperature. Diapausing adults exposed in forest to low night temperatures and transferred in October to 20°C readily reproduced at 18:6, but not 12:12 h L:D photoperiods. After 2-months at 5°C and darkness, they became insensitive to the photoperiod, matured and most of them also swarmed at 20°C in the 12:12 h L:D regime. In a Scandinavian population, diapause occurred at 18:6 h L:D and was terminated either by exposure to 5°C or by very long photoperiod (L:D 20:4 h) combined with high temperature (23°C).     

Effect of an entomopathogenic nematode,Steinernema carpocapsae on haemocyte profile and phenoloxidase activity of the Colorado potato beetle,Leptinotarsa decemlineata

The Colorado potato beetle (CPB), Leptinotarsa decemlineata Say is the most destructive insect pest of potato in many areas of the world. Little is known about the haemocyte types of the CPB and its plasma phenoloxidase (PO). In this regard, we investigated the haemocyte profile and PO of CPB and its immune response to the entomopathogenic nematode, Steinernema carpocapsae. Five types of haemocytes, the plasmatocytes (~67.4%), granulocytes (~23.5%), oenocytoids (~2.4%), spherulocytes (~0.25%) and prohaemocytes (~6.5%) were identified in fourth instar CPB larvae. Total haemocyte counts (THCs) were significantly reduced in nematode-injected insects compared with control groups (P < 0.05). Nematode cellular encapsulation observed in haemolymph of nematode-injected insects may partially explain decreased THCs. Plasma PO assay showed increased PO activity in nematode-injected insects compared with control groups (P < 0.05). Plasma PO assay on native polyacrylamide gel electrophoresis (PAGE) assay with L-3, 4-dihydroxyphenylalanine as substrate showed five bands (with molecular weights of approximately 200, 118, 68.5, 62.5 and 58.75 kDa).     

Double-stranded RNA in exosomes: Potential systemic RNA interference pathway in the Colorado potato beetle,Leptinotarsa decemlineata

Despite extensive research during the past decade elucidating the mechanism of RNA interference (RNAi) in insects, it is not clear how ingested or injected double-stranded RNA (dsRNA) triggers RNAi response in the whole body or even its progeny, which is referred to as systemic RNAi. In the present study, we aim to understand how the dsRNA delivered into cells causes systemic RNAi using Colorado potato beetle cells (Lepd-SL1). We first tested if dsRNA treatment induces systemic RNAi in Lepd-SL1 cells. Exposure of a new batch of Lepd-SL1 cells to the conditioned medium where Lepd-SL1 cells treated with dsRNA targeting inhibitor of apoptosis were grown for 6 h induced apoptosis in these new batch of cells. We hypothesized the exosomes in the conditioned medium are responsible for RNAi-inducing effect. To test this hypothesis, we isolated exosomes from the conditioned medium from Lepd-SL1 cells that had been treated with dsGFP (dsRNA targeting gene coding for green fluorescent protein) or dsLuc (dsRNA targeting gene coding for the luciferase) were grown. RNA present in the purified exosomes was analyzed to check if long dsRNA or siRNA is accumulated in them. The results from the electrophoretic mobility shift assay clearly showed that the long dsRNAs are present in the exosomes. By knockdown of candidate genes involved in endosome recycling and generation pathways, we found that Rab4 and Rab35 are involved in exosome production and transport.     

Genetic relationships of introduced Colorado potato beetle Leptinotarsa decemlineata populations in Xinjiang,China

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is an infamous invasive species worldwide that aggressively attacks potato and other Solanaceae crops. CPB was first found in China in 1993 and has since spread across 2.77 × 10⁵ km² in Xinjiang Uygur Autonomous Region. To better understand genetic variation and migration patterns, we used seven polymorphic microsatellite loci to elucidate the genetic relationships and gene flow among 10 CPB populations across Xinjiang. (i) Overall low levels of genetic diversity were detected on the entire population in Xinjiang but most of the diversity was retained among populations during invasion. (ii) The mean pairwise F_ST was low (0.071 ± 0.043) among populations. The genetic differentiation was little (pairwise F_ST 0.038 ± 0.016) between the five interior populations (Wusu, Urumqi, Jimsar, Qitai and Mulei) and Tacheng population. The six populations might come from the same genetic group via Bayesian clustering and were closely related on a neighbor‐joining tree. Combining the history data, the five interior populations may have originated from Tacheng. (iii) Gene flow was frequent, especially among the five interior populations. Individuals from the interior populations could be assigned to Tacheng at higher probabilities (means 0.518 ± 0.127) than vice versa (means 0.328 ± 0.074), suggesting that the beetle population has spread from the border to the interior in Xinjiang.     

Host-plant discrimination and evolution of feeding preference in the Colorado potato beetle Leptinotarsa decemlineata

ABSTRACT. The behaviour of newly emerged adult Colorado potato beetles on preferred hosts follows a stereotyped pattern of sampling, feeding, grooming and rest. Reduced meal sizes on less-preferred hosts is accompanied by increased sampling and frequent interruptions in feeding. A systematic increase in pre-ingestive sampling on less-preferred foodplants indicates that beetles discriminate among closely related species within the Solanaceae. This ability may depend primarily on stimuli perceived at, and near, the leaf surface. Three geographic populations of beetles have adapted to different local host plants, but have not lost their preference for feeding on an ancestral host species. Host shifts by oligophagous insects to related plant species may evolve through selection for feeding generalists in isolated populations, and may not require genetic changes affecting the perception of a particular novel host.     

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.     

Genetic variation in growth and development time under two selection regimes in Leptinotarsa decemlineata

It is possible to predict the potential range of a species on the basis of its ecological characteristics and those of the invaded ecosystem. The existence of genetic variation indicates a species’ potential to respond to new environmental conditions, thus facilitating its success as an invader. Accordingly, evolutionary and ecological approaches are needed to identify the factors explaining both species’ range and their potential to invade new areas. We combined these two approaches and studied whether genetic variation in life‐history traits under abiotic (temperature) and biotic (host plant) selection pressures contributes to the potential range expansion of Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae). We reared full‐sib families of L. decemlineata from the current northernmost European population at 15 °C (temperature below that in the current range) and 25 °C (optimal temperature) and on three potato varieties. We monitored development time, adult weight and larval‐to‐adult survival, and estimated the amount of heritable variance. The development time and adult weight of progenies were more variable between than within families. Thus, there was genetic variability in traits relevant to the ability to adapt to a colder environment (i.e., accelerate development and become heavier) allowing range expansion further north in Europe, even though low temperature increased beetle mortality. Temperature strongly affected all traits measured. Potato variety, in turn, did not strongly affect beetles’ performance. Beetle ability to adapt to a cool environment was further enhanced by the fact that size was not constrained by fast development. The results showed that beetle populations possess genetic variation allowing a response to temperature and thus have the evolutionary potential to adapt and spread beyond their current range.     

Effect of diet and feeding history on flight of Colorado potato beetle, Leptinotarsa decemlineata

We evaluated the hypothesis that Colorado potato beetle (Leptinotarsa decemlineata Say) (CPB) flight frequency is related to diet, and that it changes with duration of food unavailability or exposure to poor quality food by exposing adult overwintered and summer CPB populations to an acceptable host plant (conventional foliage), a poor host (insect resistant transgenic foliage expressing Bacillus thuringiensis tenebrionis[Btt] Cry3a toxin) and no host. Exposure to poor host and no host treatments (with or without water) decreased mean daily flight frequencies and the overall number of overwintered CPB flying, but increased the mean daily flight frequency and number of summer population CPB that flew. Overwintered CPB did not react to an absence of plants at emergence whereas summer CPB increased mean daily flight frequencies when plants and water were not available. The flight response to insect resistant foliage was similar to that for starvation treatments in both populations indicating that flight may not be triggered by Btt toxins but by starvation brought on by feeding on poor quality food. Flight was observed in all treatments for the duration of the test with two exceptions; overwintered beetles fed insect resistant foliage ceased flying after day 17 and summer beetles starved without water ceased after day 8 of a 29‐day study.