Yvan Pelletier

Environmental stresses induce the expression of putative glycine-rich insect cuticular protein genes in adult Leptinotarsa decemlineata (Say).

The deposition of cuticular proteins in insects usually occurs during the moulting process. Three putative glycine‐rich insect cuticular proteins, Ld‐GRP1 to 3, were identified and characterized from the Colorado potato beetle, Leptinotarsa decemlineata. The Ld‐GRPs contained conserved GXGX and/or GGXG sequence repeats. Ld‐GRP1 also contained a conserved AAPA/V motif commonly found in cuticular proteins. The transcripts of Ld‐GRP1 and Ld‐GRP2 were detected in the epidermal cell layer by in situ hybridization, making them putative insect cuticular proteins. The putative cuticular protein genes were highly induced by the insecticide azinphosmethyl (organophosphorous) 2–3 weeks after adult moulting. Putative cuticular protein gene expression level was higher in azinphosmethyl‐resistant beetles than in susceptible beetles. Furthermore, two of the putative cuticular protein genes were highly induced by dry environmental conditions. These results suggest that the insect might increase cuticular component deposition in the adult stage in response to environmental stresses. This ability may allow the insect to adapt to new or changing environments.

A phloem-sap feeder mixes phloem and xylem sap to regulate osmotic potential

Phloem-sap feeders (Hemiptera) occasionally consume the dilute sap of xylem, a behaviour that has previously been associated with replenishing water balance following dehydration. However, a recent study reported that non-dehydrated aphids ingested xylem sap. Here, we tested the hypothesis that the consumption of xylem sap, which has a low osmolality, is a general response to osmotic stresses other than dehydration. Alate aphids were subjected to different treatments and subsequently transferred onto a plant, where electrical penetration graph (EPG) was used to estimate durations of passive phloem sap consumption and active sucking of xylem sap. The proportion of time aphids fed on xylem sap (i.e., time spent feeding on xylem sap/total time spent feeding on phloem plus xylem sap) was used as a proxy of the solute concentration of the uptake. The proportion of time alate aphids fed on xylem sap increased: (1) with the time spent imbibing an artificial diet containing a solution of sucrose, which is highly concentrated in phloem sap and is mainly responsible for the high osmotic potential of phloem sap; (2) with the osmotic potential of the artificial diet, when osmotic potential excess was not related to sucrose concentration; and (3) when aphids were deprived of primary symbionts, a condition previously shown to lead to a higher haemolymph osmotic potential. All our results converge to support the hypothesis that xylem sap consumption contributes to the regulation of the osmotic potential in phloem-sap feeders.

Role of xylem consumption on osmoregulation in Macrosiphum euphorbiae (Thomas).

Aphids are phloem feeders that occasionally ingest xylem sap. The duration of xylem consumption by Macrosiphum euphorbiae (Hemiptera: Aphididae) was positively correlated with the level of dehydration of alate aphids of different ages after a period of starvation, supporting the hypothesis that aphids ingest xylem sap to replenish their water balance. However, the duration of xylem sap ingestion but not phloem sap consumption varied in unstarved alate adults of different ages. Furthermore, both alate and apterous aphids ingested xylem sap at the end of their life, when aphids were not dehydrated but when fecundity started to decrease. Fecundity was negatively correlated with the proportion of time spent ingesting xylem sap, and that over the entire reproductive life of alate and apterous aphids. The lower proportion of xylem ingested by apterous than by alate aphids during the first few days of adult life may be related to a higher symbiont density in apterous morphs. As previous studies have demonstrated a relationship between sucrose assimilation, which is directly influenced by fecundity and symbiont density, and osmoregulation, we suggest that xylem consumption may play a role in the osmoregulation of haemolymph of aphids.

The spread of PVYo in New Brunswick potato fields: Timing and vectors

Field tests at three sites over a period of three to four years have shown that PVYo spread in New Brunswick starts in mid-to late July when plants reach maximum height. Some 62 different genera or species of aphids were collected in experimental plots. Only seven of these were known vector species. Of the colonizing species, the alate green peach aphid,Myzus persicae (Sulzer), seems to be the most important vector. However, because it is not always present when disease spread starts, non-colonizing aphids are probably responsible for the early spread of PVYo. Five of these species of aphids were tested in the laboratory to determine their vector efficiency. A list of potential vectors is presented. The impact of these findings on the management of PVYo is discussed.CompendioPruebas de campo en tres lugares, sobre un período de cuatro años han demostrado que la diseminación de PVYo en Terranova comienza entre mediados y fines de Julio, cuando las plantas alcanzan su altura máxima. En parcelas experimentales se colectaron unos 62 géneros o especies diferentes de áfidos. Solamente siete de estos fueron especies conocidas de vectores. De las especies colonizadoras, el áfido verde del melocotoneroMyzus persicae (Sulzer) parece ser el vector más importante. Sin embargo, debido a que no siempre se encuentra presente cuando se inicia la diseminación de la enfermedad, los áfidos no-colonizantes son probablemente los responsables para una diseminación anticipada de PVYo. Se probaron en el laboratorio cinco de estas especies de áfidos para determinar su eficiencia como vector. Se presenta una lista de vectores potenciales. Se discute el impacto de estos hallazgos sobre el manejo de PVYo.

Obstacle perception by insect antennae during terrestrial locomotion

Abstract. Insect antennae bear several types of sensilla including chemo‐receptors, hygroreceptors, thermoreceptors and mechanoreceptors. A large proportion of sensilla is chemoreceptors, providing olfactory function. Pro‐prioreceptors located on the antennae provide information on the position of these organs and are used in flight control. This type of sensillum is present in most insects and might serve other functions. We tested the hypothesis that antennae are used to perceive obstacles in the path of walking beetles. When adult Colorado potato beetles, Leptinotarsa decemlineata (Say), touch an obstacle with their antennae during terrestrial locomotion, they modify the angle of their body to allow the tarsi of one prothoracic leg to reach the top of the obstacle. Our results demonstrate that antennae, by their movements and their position ahead of the beetle, provide information on the presence of the obstacle necessary to initiate step‐up behaviour. Furthermore, the change in the body angle needed to increase the reach of the prothoracic leg and step on the obstacle, is proportional to the height of the obstacle. Since the eyes are not involved in the process, normal behaviour can be performed in the dark.

Host‐plant mediated interactions between two aphid species

Herbivory induces numerous defence reactions in plants, which can in turn alter the plant quality for insects. The potato aphid, Macrosiphum euphorbiae (Thomas), and the green peach aphid, Myzus persicae (Sulzer) (both Hemiptera: Aphididae), are two important sympatric potato pests in northern France. The objective of this study was to evaluate the effect of a previous infestation of a potato plant, Solanum tuberosum L. (Solanaceae), by M. persicae or M. euphorbiae on the host attractiveness, feeding behaviour, and biological performance of M. euphorbiae subsequently colonising the plant. The preference of aphids was studied with a dual‐choice olfactometer and their feeding behaviour was monitored using the electrical penetration graph technique. Their biological performance was assessed by an in planta bioassay. Non‐infested plants were significantly more attractive to M. euphorbiae than plants pre‐infested by conspecific individuals. Aphids showed a strong reduction in the time spent ingesting phloem sap when feeding on pre‐infested plants. The biological performance of M. euphorbiae was not affected by previous conspecific infestation. Conversely, M. euphorbiae feeding behaviour was not affected on plants previously infested by M. persicae but aphids were more attracted to and had a faster population build‐up on those plants. Our results show that plant response and its effect on M. euphorbiae differed depending on the aphid species previously feeding on the potato plant. This variability in plant response could lead to competition or facilitation between aphids temporally and spatially separated, and promote dispersal under field conditions.

Resistance of three wild tuber‐bearing potatoes to the Colorado potato beetle

The resistance of Solanum okadae Hawkes & Hjert. (PI 458367), Solanum oplocense Hawkes (PI 473368), and Solanum tarijense Hawkes (PI 414150) to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Chrysomelidae: Chrysomelini), was studied. In replicated field trials all three accessions showed a high level of resistance to the beetle. No significant genetic variability between genotypes of the same species was found. Results from host acceptance behavior experiments, suitability for larval development tests, foliage consumption tests, and adult survival and oviposition tests supported the hypothesis that the mode of resistance differs between the three wild Solanum species. Solanum okadae and S. oplocense affected host acceptance and consumption. Because the beetle reacted differently to these two species it was hypothesized that the antifeedant chemical(s) differed in nature or quantity. S. tarijense contrasted with the other two species by affecting mostly adult colonization and oviposition.

3,4-Di-O-isobutyryl-6-O-caprylsucrose: the major component of a novel sucrose ester complex from the type B glandular trichomes of Solanum berthaultii hawkes (Pl 473340)

Evidence is presented that sucrose esters comprise the major portion of nonvolatile constituents in the exudate from type B glandular trichomes of Solanum berthaultii Hawkes (Pl 473340); the principal sucrose ester was characterized as 3,4-di-O-isobutyryl-6-O-caprylsucrose.

A New Approach for the Identification of Aphid Vectors (Hemiptera: Aphididae) of Potato Virus Y

ABSTRACT Potato virus Y (PVY) is one of the most economically important viruses affecting potato crops worldwide. PVY can be transmitted from potato to potato by several aphid species, most of which do not colonize the potato crop. New methods including preservation of viral RNA on stylets of aphids collected from yellow pan trap samples, polymerase chain reaction detection of PVY from the stylets of one aphid, and aphid identification using DNA barcoding were used to identify possible PVY vectors from field samples. In total, 65 aphid taxa were identified from the samples that tested positive for PVY. Among those, 45 taxa had never been evaluated for their ability to transmit PVY, and 7 were previously labeled as nonvectors. These results demonstrated that the list of PVY vectors is likely longer than previously reported and that most (if not all) species of aphids could be considered as potential vectors. This premise has important implications in the management of PVY in seed potato production.

Genotypic Variability and Mode of Action of Colorado Potato Beetle (Coleoptera: Chrysomelidae) Resistance in Seven Solanum Species

Abstract Accessions from seven wild Solanum species were evaluated in the field for resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say). The multivariate insect population density data were analyzed using factor analysis. The factors extracted corresponded to relevant phases of the insect’s life cycle and provided information on the mode of resistance (antixenosis and antibiosis) of the plant species. S. berthaultii, S. capsicibaccatum, S. jamesii, S. pinnatisectum, and S. trifidum demonstrated both antixenosis and antibiosis but expressed different levels of resistance. The mode of resistance of S. polyadenium seemed to be antibiosis and that of S. tarijense antixenosis. Genetic variability and heritability of insect resistance traits within accessions was trivial or inconsistent for all Solanum species studied.