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.     

Colonization of potato fields in eastern North Carolina by Colorado potato beetle

Rotated and non-rotated commercial potato fields were sampled intensively to follow Colorado potato beetle,Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), colonization and subsequent oviposition patterns in the spring of 1990 and 1991. Maximum densities of colonizing adults ranged from 0 to 14,891/ha and maximum egg mass densities ranged from 0 to 48,451/ha. Crop rotation generally resulted in lower potato beetle populations. Regardless of crop rotation management practices, colonization of fields planted in potatoes began at field edges and progressed inward in all fields for both years. Management of potato beetles is discussed in light of these findings.     

Response to host plant odors and aggregation pheromone by larvae of the Colorado potato beetle on a servosphere

Using a servosphere (locomotion compensator), locomotory behavior of Colorado potato beetle Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) larvae was measured in detail in response to pulsed and non-pulsed odors of hostplant and conspecific pheromone. Second instars showed decreased straightness of movement, and all larvae showed decreased speed, in response to potato odor. Change in straightness by 2nd instars was also significantly affected by the interaction of pheromone and pulsing treatments. Fourth instars showed increased positive anemotaxis in response to the combined hostplant and pheromone odors. To our knowledge, this is the first demonstration of larval behavioral responses to adult pheromone in a holometabolous insect.     

Host acceptance behaviour of Colorado potato beetle larvae influenced by potato glandular trichomes

ABSTRACT. In no-choice tests, larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), avoided contact with, and were less frequently observed feeding on, excised foliage of the resistant wild potato Solanum berthaultii Hawkes than on leaves of the cultivated potato, S.tuberosum L. For older larvae, reduced feeding was a consequence of less frequent contact with S.berthaultii leaves. However, first instars appeared unable to penetrate the adhesive barrier presented by glandular trichomes of S. berthaultii , and those that remained on the leaflets fed less often than did first instars on S. tuberosum. Removal of the trichome barrier by wiping leaflets with tissue paper did not attenuate the apparent repellent effect of S. berthaulti foliage, but led to increased incidence of feeding by first instars. Inhibition of larval feeding may therefore rely on a mechanical barrier provided by the glandular trichomes of S.berthaultii.     

Disrupting spring colonization of Colorado potato beetle to nonrotated potato fields

Overwintering Colorado potato beetles (Leptinotarsa decemlineata (Say)) were concentrated primarily within woody borders, and mortality was lower in borders than in potato fields. After overwintering, only 15–44% of live beetles were in the potato fields. In experiments with small plots, colonization of fields from woody borders was reduced ∼60% by a trap crop, either treated with adulticide or with beetles collected daily. Such trap crops, or simply pitfall traps to prevent colonization from woody borders, could significantly reduce early-season adult numbers and subsequent larval populations. However, success is dependent on the local densities of overwintered beetles, and the prevalence of arrestment behavior in the case of trap crops.     

Inhibition of Colorado potato beetle larvae by a locust proteinase inhibitor peptide expressed in potato

The cDNA for a 73-mer peptide containing two locust serine proteinase inhibitors was cloned, fused to the constitutive CaMV35S promoter and introduced into potato by Agrobacterium-mediated transformation. From 23 independent transgenic lines, three with high mRNA level and proteinase inhibitory activity were propagated in vitro and transferred to pots. The peptide from the leaves was identified by its N-terminal sequence and by K_i values against chymotrypsin and trypsin. Colorado potato beetle larvae reared on transgenic plants grew slightly but significantly more slowly than those on control plants. This supports the notion that expression of multifunctional proteinase inhibitors of insect origin might be a good strategy to improve insect resistance in plants.     

Flight take-off performance of Colorado potato beetle in relation to potato phenology

The flight take-off frequency of adult Colorado potato beetles, Leptinotarsa decemlineata (Say), from potato plants, Solanum tuberosum L. 'Red Pontiac' at the bloom stage of development was 2.2-2.5-fold that of Colorado potato beetle from plants at the vegetative stage. Tests were conducted in a flight chamber over a period of 3 h. Prefeeding Colorado potato beetles for 48 h on potato plants at the bloom or at the vegetative stage before placing them into the flight chamber resulted in the same significantly higher flight take-off frequency from potato plants at the bloom stage than from plants at the vegetative stage. These results demonstrate that the factor in potato plants in bloom that stimulates the flight take-off of the Colorado potato beetle is independent of the feeding history of the beetles and begins acting only when the beetles are in the presence of the plant. According to these results, the dispersal of adult Colorado potato beetles from potato fields in bloom to younger potato fields with plants at the vegetative stage, previously reported in the literature, is at least partly explained by the effect of plant phenology on the frequency of flight take-off. Results confirm the value of planting potato fields of similar phenology over as wide an area as possible to reduce Colorado potato beetle dispersal between fields. Results also imply that staggering the planting dates of conventional potato refuge areas near Colorado potato beetle transgenic or conventionally resistant potato fields is a sound management practice, because it promotes the movement of wild beetles over to the adjacent younger resistant crops.     

Colorado potato beetle resistant somatic hybrid potato plants produced via protoplast electrofusion

Leptines are natural glycoalkaloids found only in certain selections of the wild potato speciesSolanum chacoense. These rare glycoalkaloids have been identified to be phytochemical defensive agents against insect herbivores such as the Colorado potato beetle (CPB). In an attempt to introduce this CPB resistance into the cultivated potatoS. tuberosum, interspecific somatic hybrid plants were developed between a dihaploid ofS. tuberosum and a high leptine-producing germplasm selection ofS. chacoense. The somatic hybrid was fused using protoplast electrofusion and regeneration techniques. Selection of interspecies fusion cell lines was based on hybrid vigor in protoplast-callus (p-callus) growth, on shoot regeneration from p-calli, and on characteristic appearance of anthocyanin pigment. This selection system was highly efficient and 12 of 13 fully regenerated plants were identified as somatic interspecies hybrids, as determined by the analyses of morphologic biochemical, and isozyme markers. In vitro insect bioassays demonstrated that the hybrids averaged a threefold reduction in leaf consumption by the CPB when compared to cultivated potatoes.     

Orientation of Colorado potato beetle to natural and synthetic blends of volatiles emitted by potato plants

1 Behavioural responses of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), to volatiles emitted from solanaceous host plants (potato and tomato), a non‐host legume (soybean), and 13 synthetic blends or three individual chemicals emitted by potato plants were investigated in laboratory bioassays. 2 Both male and female CPB were attracted to volatiles emitted by mechanically damaged potato foliage, but not to mechanically damaged tomato foliage; CPB offered a choice between the two damaged solanaceous plants did not show a preference. 3 Among 16 odourous blends or individual chemical components of potato plant emissions tested, six blends were attractive, two were repellent, and eight elicited no preference in laboratory bioassays. Volatile blends containing relatively high amounts of the green leaf volatiles (E)‐2‐hexen‐1‐ol and (Z)‐3‐hexen‐1‐ol, or the sesquiterpene β‐ caryophyllene, were unattractive or repellent. Minimal blends attractive to CPB were comprised of (Z)‐3‐hexenyl acetate (±)‐linalool and methyl salicylate: the combination of all three chemicals elicited sexually dimorphic attraction of males; two component blends comprised of (Z)‐3‐hexenyl acetate and either (±)‐linalool and methyl salicylate attracted both sexes. Individual compounds were inactive. No significant difference was noted between two attractive blends, or an attractive synthetic blend vs. mechanically damaged potato foliage. 4 These results show that CPB are attracted to blends of specific chemicals emitted by their host plants and provide a basis for the use of plant attractants as a component of integrated management of pestiferous populations.     

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.     

Colorado potato beetle larvae on potato plants expressing a locust proteinase inhibitor

The natural defence system of plants often involves inhibitors of digestive enzymes of their pests. Modem and environmental-friendly methods try to increase this plant resistance by expressing heterologous protease inhibitors in crops. Here we report the effects of expressing a gene from desert locust (Schistocerca gregaria) encoding two serine protease inhibitors in potato on Colorado potato beetle (Leptinotarsa decemlineata) larvae. The gene encoding both peptides on a single chain was used for Agrobacterium-mediated transformation of potato plants. The presence of the active inhibitor protein in the leaves was verified. The feeding bioassays in the laboratory showed that despite the low level of the peptide in leaves, CPB larvae on transgenic plants have grown slightly but significantly more slowly than those on control potato plants. The results support the notion that expression of multifunctional proteinase inhibitors of insect origin in plants might be a good strategy to improve insect resistance.     

Genetic transformation of potato with nptII-gus marker genes enhances foliage consumption by Colorado potato beetle larvae

Little is known about the effect of transgenic plants containing commonly used marker genes, such as aph(3)II (nptII encoding neomycinphosphotransferase) and uidA (gus encoding -glucuronidase) on insect feeding behaviour. We report here, for the first time, that transgenic potato plants containing only nptII and gus marker genes enhance foliage consumption by the Colorado potato beetle (CPB, Leptinotarsa decemlineata S.). Transformation of potato cultivar Désirée was performed with Agrobacterium tumefaciens. Internode explants were inoculated with different strains of bacteria, carrying either nptII-gus or nptII alone. A total of 180 transgenic and untransformed control plants were grown in the greenhouse for the analysis of food consumption by CPB. For each transformed and untransformed line tested, four bioassays were conducted each consisting of 10 second-instar larvae feeding independently on a 2 cm diameter leaf disc for 20 h. Our data show up to 50% increase of mean foliage consumption on plants transformed with the nptII-gus construct, indicating that transgenic plants containing these marker genes can affect the feeding behaviour of the insects. These results were obtained from the primary regenerants (R₀ lines) as well as from tuber-derived plants (R₁ lines). Further tests with transgenic plants containing the nptII marker gene only, showed no significant difference in feeding when compared to untransformed control plants, allowing us to rule out a direct effect of this marker gene on foliage consumption by the insect larvae. It is suggested that gus protein is involved in the increase of foliage consumption by CPB.     

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).     

Suppression of larval Colorado potato beetle growth and development by digestive proteinase inhibitors

Evidence is presented that the Colorado potato beetle (CPB) (Leptinotarsa decemlineata (Say)) depends, at least partially, on cysteine proteinases for protein digestion. Midgut homogenates of CPB larvae have a mildly acidic pH and exhibit major proteolytic activity in the mildly acidic pH range. This proteolytic activity is activated by reducing agents, is inhibited by E-64 (a specific cysteine proteinase inhibitor), and is not inhibited by serine proteinase inhibitors. In addition, consumption of E-64 treated potato leaves by CPB larvae at rates as low as 0.8 g/cm² of leaf tissue has a deleterious effect on larval growth and development.

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Résumé Les protéinases intestinales des larves de Leptinotarsa decemlineata sont en partie caractérisées par les pH limitant leur activité, et par l'effet d'inhibiteurs de protéinases de spécificités connues. Les protéinases ont été testées avec la méthémoglobine tritiée comme substrat et nous avons déterminé les taux relatifs de peptides radioactives TCA solubles, libérées, dans des conditions précises, pour des pH compris entre 2,0 et 12,0. Le taux le plus élevé d'activité protéolytique a été observé pour des pH 5,0 à 6,0, bien qu'il y ait eu une activité appréciable aux pH 4,0 et 8,0. Parmi les inhibiteurs examinés, le E-64, inhibiteur protéinase cystéine très sélectif, a été le plus efficace sur l'activité protéinase. La pepstatine, inhibiteur protéinase aspartique, a été actif, mais seulement dans une gamme plus moin de pH. Les inhibiteurs protéinase sérine, ont été pratiquement inactifs sur l'activité protéinase.Chez des larves de doryphores nourries de feuilles de pommes de terre traitées avec différentes concentrations de E-64 ou de pepstatine, la consommation de E-64 a retardé fortement la croissance larvaire et le développement, la pepstatine a provoqué un retard du développement plus limitée.Nos résultats suggèrent que le doryphore dépend, tout au moins partiellement, des protéinases cystéine pour l'assimilation des protéines.

     

Antifeedant and toxic effects of drimanes on Colorado potato beetle larvae

Among the drimane compounds tested, the dialdehydes polygodial and warburganal were the most active as antifeedants against Colorado potato beetle larvae, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in a dual-choice assay with potato, Solanum tuberosum L., leaf discs. Lactones were less effective. Direct observations showed that decreased feeding on leaf discs treated with polygodial and warburganal was accompanied by increased locomotry activity. Topical application of these two compounds on the insect's cuticle decreased food intake of untreated leaf discs, indicating that besides deterrent effects, toxic properties of these molecules influence feeding behaviour.     

Sequence matters – selective adaptation in electroantennographic response to binary odour mixtures by the Colorado potato beetle

Chemically mediated behaviour of insects is often strongly affected by mixtures of odour stimuli and their temporal characteristics. Both sensory transduction and central processing of odour mixtures can give rise to several different kinds of interaction, which can influence how individual components are perceived and processed. In particular, odour mixtures have been examined in model experiments as premixed binary mixtures in comparison with pure odour stimuli. Only in few experiments, the influence of the temporal structure of odour mixtures on odour perception has been taken into account. Natural odour stimuli often have a pulsed structure and may in general be superimposed on a background of irrelevant or interfering compounds, which can fluctuate with different frequencies, depending on their source. To achieve a better representation of these natural conditions, our odour mixing experiments apply a new kind of stimulation protocol: odours were not premixed but superimposed with a specific time pattern; one odour stimulus was presented as a longer persisting background and the second stimulus was a superimposed short test signal. To gain an overview of odour interaction patterns in the Colorado potato beetle by causing adaptation of one receptor population at naturally occurring levels of concentration and time intervals, electroantennographic recordings were made on excised antennae. A matrix of 12 stimulus compounds led to 132 pairs of compounds tested, each in the role of background and test stimulus. In 64 cases, the interaction was significantly different, when the role of background and stimulus was exchanged. Interaction patterns ranging from no interference (independence) to suppression were found and assigned to four clearly distinguishable types. We discuss that the observed effects of the presentation sequence in odour mixtures may contribute to the mechanisms of olfactory pattern recognition and olfactory contrast perception by insects.     

Family structured patterns of mortality in the false Colorado potato beetle

Abstract. 1. The distribution of mortality within and among groups of immature Leptinotursu juncta (Germar) (Coleoptera: Chrysomelidae) was studied in the field at three points in the life-cycle in order to test whether the fates of individuals occupying the same host plant were non-independent.
2. Studies were conducted on eggs subject to cannibalism and predation, on newly hatched larvae subject to predation, and on older larvae subject to parasitism by Myiophurus doryphorue (Riley), a tachinid fly.
3. At all three points in the life-cycle the variance in group-specific survivorship rates was demonstrated to be significantly greater than expected when individual deaths are distributed randomly among groups, with standardized variances ranging from 42% to 52% of the maximum possible.
4. A statistically significant positive correlation was shown between the number of individuals in a group and the group-specific survivorship rate at all three life stages.
5. The distribution of genetic variants within and among groups of larvae showed the groups to be mixtures of full and half siblings, with an average coefficient of genetic relatedness, r , equal to 0.38.