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.

     

Intraspecific mitochondrial DNA variation in the Colorado potato beetle,Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Restriction endonuclease analyses of mitochondrial DNA (mtDNA) were used to examine genetic variability and population structure inLeptinotarsa decemlineata (Say). A group of three enzymes, EcoRI, HpaI, and PstI, was used to reveal polymorphism both within and among some of the 10 populations tested, yielding 16 haplotypes in combination. The frequencies of these 16 haplotypes differed significantly across geographic regions, indicating some partitioning of mtDNA haplotypes. Estimates of mtDNA sequence divergence (δ) between haplotypes ranged from 0.016 to 0.135%, suggesting local differentiation of mtDNA in some populations. Analysis of these data suggests that Texas was colonized by more than one mtDNA lineage, most likely originating in Mexico. We hypothesize that a larger founder size for the initial introductions or high levels of variability in the parent population at the edge of the CPB expanding range led to the initial partitioning of haplotypes observed in samples from Texas.     

A proctolin-like peptide and its immunocytochemical localization in the Colorado potato beetle,Leptinotarsa decemlineata

Summary Evidence is presented that neurons in the adult Colorado potato beetle contain a proctolin-like substance. By use of immunocytochemical methods the location of immunoreactive neurons in the central and stomatogastric nervous systems is described. No such neurons were found in the proto- and deutocerebrum or optic lobe. Few immunoreactive neurons are present in the tritocerebrum and numerous proctolin-immunoreactive neurons occur in all ventral ganglia and in the frontal ganglion. Two groups of neurosecretory cells in the suboesophageal ganglion contain a proctolin-immunoreactive substance. In these cells this material is co-localized with a bovine pancreatic polypeptide/FMRF amide-like substance and with a vasopressin/vasotocin/oxytocin-like substance. Proctolin-immunoreactive axon terminals were found on the musculature of the fore- and hindgut and of the vas deferens, and on some segmental muscles. Furthermore, proctolin-immunoreactive neurosecretory axon terminals were found in the corpus cardiacum. The proctolin-like substance may therefore function both as a neurotransmitter/neuromodulator and as a neurohormone. The presence of a proctolin-like substance was also demonstrated with a sensitive bioassay. On fractionation of extracts of the nervous systems of Leptinotarsa decemlineata with high performance liquid chromatography most of the proctolin-like bioactive material comigrated with authentic proctolin. This shows that a proctolin-like substance in this insect is very similar to, if not identical with, the known pentapeptide proctolin.     

Starvation induced stress and the susceptibility of the Colorado potato beetle,Leptinotarsa decemlineata,to infection by Beauveria bassiana

Starvation of second instar Colorado potato beetle larvae for 24h immediately after treatment with Beauveria bassiana conidia increased susceptibility to the pathogen and subsequent sporulation of cadavers but decreased time to larval death. In feeding studies, B. bassiana-treatment had no effect on subsequent larval development, and mortality occurred 5-6 days after treatment. Twenty-four hours of starvation alone retarded subsequent larval development but did not affect mortality. Mortality of B. bassiana-treated starvation stressed larvae occurred 4-5 days after treatment. Both B. bassiana treatment and 24h starvation significantly reduced total foliage consumption and daily weight gains. On the day of treatment, B. bassiana had no effect on the efficiency with which food was converted to biomass (ECI). ECI was not affected by B. bassiana or starvation alone on the day following treatment but was significantly affected by a combination of both. When larvae were exposed to a range of limited food quantities, ECI decreased with decreasing food availability but only extreme stress (starvation for 24h) increased susceptibility to B. bassiana. Topical application of Dacryodes excelsa resin (an antifeedant) to potato leaves caused a concentration dependent reduction in foliage consumption and weight gain by second instar larvae but did not affect larval mortality. When larvae were exposed to a fixed concentration of B. bassiana and a range of antifeedant concentrations there were significant linear relationships between 24h larval weight gain and mortality and 24h larval weight gain and sporulation. The interaction between starvation stress and the susceptibility to B. bassiana infection is discussed and its possible implications in pest management considered.     

Incidence of natural enemies of the Colorado potato beetle,Leptinotarsa decemlineata [Coleoptera: Chrysomelidae] on a native host in Mexico

In central Mexico, the center of origin forLeptinotarsa decemlineata (Say) and its principal host plants,L. decemlineata is associated with a diverse complex of natural enemies. Observations during 2 years in Morelos, Mexico revealed 4 species of asopine pentatomids, 7 species of foliar searching carabids, and 2 coccinellids among the predators ofL. decemlineata. Parasitoids include 3 species of tachinids andEdovum puttleri Grissel, an eulophid egg parasitoid. These natural enemies include several predators that have not previously been reported attackingL. decemlineata. University of Maine Agriculture Experiment Station No. 1553     

Effects of four Bacillus spp. of soil origin on the Colorado potato beetle Leptinotarsa decemlineata (Say)

Four species of Bacillus were isolated from soil in an effort to find safe, effective and alternative biological control agents against plant pests. These bacteria were identified as Bacillus pumilus, Bacillus sphaericus, Bacillus megaterium and Bacillus cereus on the basis of fatty acid methyl ester analysis and carbon utilization profiles by using Microbial Identification and Biolog Microplate Systems. Laboratory experiments carried out to determine the insecticidal activities of these isolates showed that B. pumilus caused 95.7 and 26.7% mortality and B. sphaericus caused 74.5 and 23.3% mortality of Leptinotarsa decemlineata larvae and adults, respectively. B. cereus and B. megaterium showed 51.1 and 29.7%, respectively, of L. decemlineata larvae. This study presents at least two Turkish isolates from the genus Bacillus showing high insecticidal activity against L. decemlineata.     

Diffuse serotoninergic neurohemal systems associated with cerebral and suboesophageal nerves in the head of the Colorado potato beetle Leptinotarsa decemlineata

We analyzed the anatomy of two diffuse neurohemal systems for serotonin in the head of the Colorado potato beetle Leptinotarsa decemlineata by means of immunohistochemistry. One system is formed by axons from two bilateral pairs of neurons in the frontal margin of the suboesophageal ganglion that enter the ipsilateral mandibular nerve, emerge from this nerve at some distance from the suboesophageal ganglion, and cover all branches of the mandibular nerve with a dense plexus of immunoreactive axon swellings. The other system is formed by axons from two large neurons in the frontal ganglion that enter the ipsilateral frontal connectives, emerge from these connectives, and form a network of axon swellings on the labroforntal, pharyngeal, and antennal nerves and on the surface of the frontal ganglion. Immunohistochemical electron microscopy demonstrated that the axon swellings are located outside the neural sheaths of the nerves and hence in close contact with the hemolymph. We therefore suggest that these plexuses represent extensive neurohemal systems for serotonin. Most immunoreactive terminals are in direct contact with the hemolymph, and other terminals are closely associated with the muscles of the mandibles, labrum, and anterior pharynx, as well as with the salivary glands, indicating that these organs are under serotoninergic control.     

Fecundity and egg fertility in the adult Colorado beetle (Leptinotarsa decemlineata) surviving larval infection by the fungus Beauveria bassiana

Secondary effects of the entomopathogenic hyphomycete Beauveria bassiana (Bals.) Vuill. were investigated on adults of Leptinotarsa decemlineata Say (Coleoptera:Chrysomelidae) treated as newly moulted 4th-instar larvae. Fecundity and egg hatching were monitored in surviving females mated with surviving males. When reared at 22°C, adult survivors showed a lessening of their reproductive potential during their whole life. According to the fungal inoculum dosage, the reductions of the total number of eggs laid per female and the mean number of eggs per egg mass ranged from 20% to 56% and from 18% to 46%, respectively. In contrast, at 25°C, the fecundity of survivors was not affected by the fungal infection. This variability of the secondary effects of B. bassiana according to temperature conditions might be related to the lower infection level of treated larvae at 25°C. Moreover, at both temperatures, eggs laid by females surviving fungal infection as larvae were as fertile as eggs laid by control insects. It is concluded that secondary effects of B. bassiana on the fecundity of the Colorado Potato Beetle are temperature-dependent and that they could become negligible at high temperatures under field conditions.

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Résumé Les effets secondaires de l'hyphomycète entomopathogène, Beauveria bassiana (Bals.) Vuill. sur la fécondité et la fertilité des insectes survivant à l'infection fongique ont été étudiés chez les adultes du doryphore Leptinotarsa decemlineata Say (Coleoptera:Chrysomelidae) issus de larves contaminées en début de 4ème stade. Les insectes maintenus à 22°C ont présenté une réduction de leur potentiel reproductif. Ainsi, suivant la dose d'inoculum fongique, le nombre total d'oeufs pondus par femelle et le nombre moyen d'oeufs par opplaque ont baissé de 20% à 56% et de 18% à 46%, respectivement. En revanche, à 25°C la fécondité des adultes survivants n'a pas été affectée par la maladie. Cette variabilité en fonction des conditions thermiques peut être liée à la diminution de l'effet-dose du champignon sur les larves à 25°C par rapport à 22°C. Par ailleurs, quelles que soient les conditions thermiques (22°C ou 25°C) on ne constate aucun changement significatif de la fertilité des oeufs pondus par les femelles survivantes. Les auteurs concluent que les effets secondaires de B. bassiana sur la fécondité du doryphore dépendent des conditions thermiques et qu'ils pourraient devenir négligeables à des températures élevées en plein champ.

     

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.     

Effect of vermicompost on nutrition and intermediary metabolism of Colorado potato beetle,Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)

Colorado potato beetle (CPB) is the important pest of potato throughout the world. The study showed the effects of vermicompost on nutritional indices, digestive enzyme activities and intermediary metabolism of the larvae and the adults of CPB. Vermicompost affected significantly the efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD) in addition to activities of carbohydrases and proteases in both larvae and adults. Amount of total phenol compounds increased in the leaves of the potatoes grown on the soil containing 30% of vermicompost compared to control and it were amended by 15% of vermicompost. In case of intermediary metabolism, activities of aspartate aminotransferase and γ-glutamyl transferase showed no significant differences in the control and the treated larvae, but those were fluctuated upper and lower when 15% of vermicompost was added into growth plots. The amount of low-density lipoproteins (LDL) and high-density lipoproteins (HDL) in the larvae of CPB showed no significant differences among treatments. However, the amounts of LDL, HDL, glycogen and protein of the adults significantly increased using 30% of vermicompost. Results of the current study clearly revealed significant effects on some physiological processes in CPB fed on the plants grown in the different vermicompost treatments.     

A fine structural survey of the development of the adult fat body of Leptinotarsa decemlineata

The fat body of a female Colorado potato beetle, Leptinotarsa decemlineata, at adult ecdysis, contains a large number of protein granules which are composed of light and dark zones. Part of the light zone in some of these granules is believed to be urate. During the first two days after adult ecdysis, fat body development is not essentially different in females reared either under long- or short-day conditions. Protein granules and large vacuoles disappear and the first cell organelles are regenerated. The effect of the photoperiod on the histological structure of the fat is expressed after these events. In females reared under long-day conditions, the fat body becomes specialized for vitellogenin synthesis. Under short-day conditions, the fat body stores massive amounts of lipid until day 6 after adult ecdysis. Then the first electron-dense protein granules develop near the nucleus, and on day 10 the first autophagic vacuoles are seen. These structure changes are discussed in connection with the known biochemical properties of the adult faty body of Leptinotarsa.     

Rearing Colorado Beetles (Leptinotarsa decemlineata) on lyophilised potato leaves

Élevage de doryphore (Leptinotarsa decemlineata) sur du feuillage de pomme de terre lyophilisé Pour élever en permanence une souche de doryphore en jours longs, on a utilisé du feuillage de pomme de terre lyophilisé, sans avoir besoin de changer de variété. l'élevage obtenu, exigeant quant à sa maintenance, donne des résultats comparables à celui des témoins en ce qui concerne le poids à l'émergence, le comportement général et allonge la durée de vie. L'oviposition est, en revanche, perturbée.     

Structure-activity studies of modified citrus limonoids as antifeedants for Colorado potato beetle larvae, Leptinotarsa decemlineata

Limonin and ten structurally modified limonins were evaluated as antifeedants against 4th instar larvae of the Colorado potato beetle, Leptinotarsa decemlineata Say, in no-choice leaf dics assays. The epoxide and furan groups were shown to be essential structural requirements for high antifeedant activity.

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Résumé Le pouvoir phagodissuasif de la limonine et de 10 limonines dont la structure avait été modifiée a été évalué sur des disques de feuilles de Solanum tuberosum offerts à des larves du 4ème stade de L. decemlineata. Aucune activité dissuasive n'ayant été observée avec le tétrahydrolimonine ou le déoxylimonine, l'anneau furane et le groupe époxy sont donc nécessaires pour obtenir cette activité. Ni la réduction de la fonction 7-kéto, ni la rupture de l'anneau A de la limonine n'ont eu d'effêt sur cette activité. La réduction des fonctions 16-carbonyl et 7-kéto de la limonine ont diminué l'activité, mettant en évidence une action possible de l'anneau D-lactone dans l'activité phagodissuasive. Tandis que la déépoxydation de la limonine entraîne une perte d'activité totale, une restauration partielle de cette activité a pu être obtenu par une réduction ultérieure de la fonction 7-kéto.

     

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.     

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.