Andrei Alyokhin

Colorado potato beetle resistance to insecticides

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is widely regarded as the most important insect defoliator of potatoes. Its current range covers about 16 million km2 in North America, Europe, and Asia and continues to expand. This insect has a complicated and diverse life history, which is well-suited to agricultural environments, and makes it a complex and challenging pest to control. Dispersal, closely connected with diapause, feeding, and reproduction, allow the Colorado potato beetle to employ “bet-hedging” reproductive strategies, distributing its offspring in both space (within and between fields) and time (within and between years). The Colorado potato beetle played a large role in creating the modern pesticide industry, with hundreds of chemicals tested against it. High selection pressure, together with natural propensity to adapt to toxic substances, eventually resulted in a large number of insecticide-resistant Colorado potato beetle populations. Since the middle of the last century, the beetle has developed resistance to 52 different compounds belonging to all major insecticide classes. Resistance levels vary greatly among different populations and between beetle life stages, but in some cases can be very high (up to 2,000-fold). Known mechanisms of Colorado potato beetle resistance to insecticides include enhanced metabolism involving esterases, carboxylesterases and monooxygenases, and target site insensitivity, as well as reduced insecticide penetration and increased excretion. There is also some evidence of behavioral resistance. Resistance mechanisms are sometimes highly diverse even within a relatively narrow geographical area. Resistance is usually inherited as an incompletely dominant or incompletely recessive trait, with one or several genes involved in its determination. Because of pleiotropic effects of resistant alleles, insecticide-resistant beetles often have reduced relative fitness in the absence of insecticides. Rotating different classes of insecticides and reducing insecticidal pressure on pest populations by provision of temporal and spatial refuges from exposure to toxins have been proposed to delay evolution of resistance. However, insecticide resistance in this insect will likely remain a major challenge to the pest control practitioners. Still limited understanding of beetle biology, its flexible life history, and grower reluctance to adopt some of the resistance management techniques create impediments to successful resistance management. Overcoming these obstacles is not an easy task, but it will be crucial for sustainable potato production.ResumenEl escarabajo de Colorado de la papa [(Leptinotarsa decemlineata (Say)] es considerado el insecto defoliador más importante de la papa. Su acción cubre una área de 16 millones de km2 en Norteamérica, Europa y Asia y continúa expandiéndose. Este insecto tiene un ciclo de vida complicado y diverso, el cual esta bien adecuado a entornos agrícolas y lo hace una plaga difícil de controlar. Su dispersión, íntimamente conectada con su quiescencia, hábitos de alimentación y reproducción permite al escarabajo de Colorado de la papa emplear estrategias de reproducción de “riesgo calculado”distribuyendo su descendencia en espacio (dentro del campo y entre campos) y tiempo (dentro y entre años). El escarabajo de Colorado de la papa jugó un rol muy amplio en la creación de la industria moderna de pesticidas, con cientos de químicos evaluados para su control. La alta presión de selección, junto a la propensión natural para adaptarse a las sustancias tóxicas, resultó en un gran número de poblaciones resistentes a los insecticidas. Desde mediados del siglo pasado, el escarabajo ha desarrollado resistencia a 52 diferentes compuestos pertenecientes a todas las clases importantes de insecticidas. Los niveles de resistencia varían mucho entre las diferentes poblaciones y estadíos en el ciclo de vida, pero en algunos casos pueden variar mucho más (hasta 2,000 veces). Los mecanismos conocidos de resistencia de este escarabajo a los insecticidas incluyen un elevado metabolismo de las esterasas, carboxilesterasas y monooxigenasas e insensibilidad al sitio objetivo, lo mismo que una penetración del insecticida reducida y excreción incrementada. También hay evidencia de resistencia por comportamiento. Los mecanismos de resistencia son a veces altamente variados, aun dentro de una reducida área geográfica. La resistencia es a menudo heredada como un carácter incompletamente dominante o incompletamente recesivo, con uno o varios genes involucrados en su determinación. Debido a los efectos pleiotrópicos de alelos resistentes, los escarabajos resistentes tienen una aptitud relativa reducida en ausencia de insecticidas. La rotación de diferentes clases de insecticidas y la reducción de la presión insecticida sobre las poblaciones de insectos por provisión de refugios temporales y espaciales contra la exposición de toxinas han sido propuestas para demorar la evolución de la resistencia. Sin embargo, la resistencia a insecticidas de este insecto permanecerá siendo un desafío para los practicantes de control de plagas. Todavía hay un limitado conocimiento sobre la biología del escarabajo, su ciclo de vida flexible y la renuencia del productor para adoptar algunas de las técnicas de manejo de la resistencia impiden el manejo exitoso de la resistencia. El vencer estos obstáculos no es tarea fácil, pero será importante para una producción sostenible de papa.

Changes in a lady beetle community following the establishment of three alien species

A number of recent studies indicated that establishment of exotic lady beetles (Coleoptera: Coccinellidae) may have adverse affects on native lady beetle species. In the present study, we analyzed changes in coccinellid community inhabiting potato crops in northern Maine over the past 31 years. Prior to 1980, lady beetle communities were comprised almost exclusively of the two native species, Coccinella transversoguttata Brown and Hippodamia tredecimpunctata(Say). Starting 1980, an exotic species Coccinella septempunctata L. became permanently established in potato crops and quickly started to dominate lady beetle community. Two other exotic species, Harmonia axyridis(Pallas) and Propylea quatordecimpunctata(L.) became prominent members of the lady beetle community in 1995 and 1996. Invasion by exotic species was followed by a significant decline in the abundance of C. transversoguttata and H. tredecimpunctata, and a significant increase in the overall diversity of lady beetle community. The abundance of aphid prey was substantially reduced after the establishment of H. axyridis. The observed trends demonstrate the profound effects that exotic natural enemies may have on target and non-target native species, and highlight the importance of their thorough evaluation before initiating biological control programs.

On-Soil Movement and Plant Colonization by Walking Wingless Morphs of Three Aphid Species (Homoptera: Aphididae) in Greenhouse Arenas

Abstract Potato aphid, Macrosiphum euphorbiae (Thomas); green peach aphid, Myzus persicae (Sulzer); and buckthorn aphid, Aphis nasturtii Kaltenbach are polyphagous herbivores that commonly colonize potato plants, Solanum tuberosum L., in the northeastern United States and Canada. Their movement influences spatial and temporal patterns of viral spread within potato fields. We investigated aphid movement between potato plants early in the season, with a particular focus on their ability to walk over bare soil. On average, aphids survived 1.16 ± 0.04 d (mean ± SE) on the surface of bare soil; all of them dying within 3 d. Wingless aphids did not leave potato plants that were adequate as a food supply. When forcibly removed from the host plant and released on the soil surface, all three species colonized the nearest plant within 1 h. However, when given no other choice, a significant proportion of aphids was fully capable of colonizing potato plants as far as 180 cm away from the point of release. Potato aphid, which is the largest, was the most mobile of the three species. The green peach aphid was intermediately mobile, and the buckthorn aphid was the least mobile species.

Susceptibility of imidacloprid-resistant Colorado potato beetles to non-neonicotinoid insecticides in the laboratory and field trials.

Repeated use of neonicotinoid insecticides has resulted in the first reported cases of Colorado potato beetle (Leptinotarsa decemlineata (Say)) resistance to imidacloprid. In the laboratory we determined susceptibility of the imidacloprid-resistant Colorado potato beetles from a population in Southern Maine to other insecticides currently registered for use on potato. This population was about 30-fold resistant to imidacloprid and could not be effectively controlled by its applications. Control mortality was significantly higher for the imidacloprid-resistant larvae than for the susceptible larvae, suggesting that fitness disadvantages may be associated with the resistance trait. Resistant larvae exhibited significantly less mortality than susceptible larvae when exposed to cyfluthrin, carbaryl, azinphosmethyl, and methamidophos. Their susceptibility to oxamyl was also somewhat reduced, although it did provide nearly 100% mortality at the highest concentration tested. Disulfoton was highly toxic to the resistant larvae. Oxamyl killed about 40% of the adults in greenhouse assays with potted potato plants, altered their feeding behavior (fewer adults up on plants), and reduced defoliation by more than 90%. Disulfoton was not lethal to adults, but significantly suppressed their feeding. In field trials with the resistant population, oxamyl and imidacloprid + spinosad provided the best beetle control. Novaluron had no detectable effect on beetle densities. There was little difference between the plots treated with imidacloprid or thiamethoxam and the untreated control. Our results suggest that insecticide rotation may be a valuable option for managing imidacloprid-resistant Colorado potato beetle populations. We also had a good consistency between the results of the Petri dish, greenhouse, and field experiments, indicating that screening under laboratory confinement may be useful when developing initial recommendations to potato growers in areas affected by resistance to neonicotinoids.ResumenEl uso reiterado de insecticidas neonicotinoides ha dado como resultado, en los primeros casos reportados sobre el escarabajo de Colorado de la papa [Leptinotarsa decemlineata (Say)], resistencia al imidacloprid. En el laboratorio hemos determinado susceptibilidad de los escarabajos resistentes al imidacloprid, a otros insecticidas registrados actualmente para su uso en papa, en una población del Sur de Maine. Esta población fue alrededor de 30 veces más resistente al imidacloprid y no pudo ser efectivamente controlado con su aplicación. La mortalidad en el testigo fue significativamente alta para las larvas resistentes al imidacloprid que en larvas susceptibles, sugiriendo que este hecho puede estar asociado con la característica de resistencia. Las larvas resistentes mostraron significativamente menos mortalidad que las susceptibles cuando estuvieron expuestas al cyfluthrin, carbaryl, azinphosmetyl y metamidophos. Su susceptibilidad al oxamyl fue en cierta forma reducida, aunque proporcionó cerca del 100% de mortalidad a una alta concentración. El disulfoton fue altamente tóxico a las larvas resistentes. El oxamyl mató alrededor de un 40% de adultos en pruebas de invernadero con plantas en maceta, alteró su hábito de alimentación (pocos adultos sobre las plantas) y redujo la defoliación por más del 90%. El disulfoton no fue letal para adultos, pero suprimió significativamente su alimentación. En pruebas de campo con la población resistente, oxamyl e imidacloprid + spinosad, proporcionaron el mejor control del escarabajo. Novaluron no tuvo efecto detectable sobre la densidad del escarabajo. Hubo poca diferencia entre las parcelas tratadas con imidacloprid o thiamethoxam y el testigo no tratado. Nuestros resultados sugieren que la rotación de insecticidas puede ser una opción valiosa para manejar las poblaciones del escarabajo de Colorado de la papa. También hemos tenido consistencia entre los resultados de los experimentos en placa Petri, invernadero y campo, lo cual indica que el tamizado en el laboratorio puede ser útil cuando se desarrollen las recomendaciones iniciales para los cultivadores de papa en áreas afectadas por resistencia a neonicotinoides.

Persistence and Inheritance of Costs of Resistance to Imidacloprid in Colorado Potato Beetle

Abstract Reduced fitness among resistant versus susceptible individuals slows resistance evolution and makes it easier to manage. A loss of resistance costs could indicate novel adaptations or mutations contributing to resistance. We measured costs of resistance to imidacloprid in a Massachusetts resistant population compared with a Massachusetts susceptible population in 1999 in terms of fecundity, hatching success, egg development time, and sprint speed. Resistance was additive and seemed to be polygenic with high heritability. The fecundity cost appeared overdominant in 1999, and the hatch rate cost was partly recessive in 1999, but neither was significantly different from dominant or recessive. In 2004, we repeated our measures of resistance costs in Massachusetts in terms of fecundity and hatching success, and we added a new resistant population from Maine. In 2005, we compared development time of Maine resistant and the laboratory susceptible colony eggs. Significant fecundity costs of resistance were found in both population in both 1999 and 2004, and significant egg developmental time costs were found in 1999 and 2005. However, the hatching success costs of resistance were significant in 1999 and not apparent in 2004, suggesting some modification or replacement of the resistance genes in the intervening time.

Interplant Movement of Potato Aphid (Homoptera: Aphididae) in Response to Environmental Stimuli

Abstract Potato aphid, Macrosiphum euphorbiae (Thomas), is a highly mobile aphid species that dominates aphid communities in Maine potato fields and may contribute to virus transmission between potato plants. We studied effects of simulated rain, wind, mechanical raking, fungicide application, reflective mulch, and predator [lady beetle, Harmonia axyridis (Pallast)] on the interplant movement of wingless adult potato aphids in greenhouse experimental arenas that imitated small segments of a potato field. The number of aphids dispersing from the central plant in the arena after a tested perturbation was recorded. Experiments were repeated with 3- to 4-wk-old plants with nonoverlapping canopies and with 4- to 5-wk old plants with canopies overlapping within rows. Aphids moved between potato plants even when canopies did not overlap and without any environmental perturbations. However, more aphids moved between larger plants with overlapping canopies. Rain significantly encouraged aphid movement between plants with nonoverlapping canopies. Wind, rain, and mechanical raking significantly encouraged aphid movement between plants with overlapping canopies. Regardless of canopy overlap, most aphids moved within the rows of potato plants. However, there was also considerable movement between the rows, even though the aphids had to walk over bare soil.

Abundance of Native and Non-Native Lady Beetles (Coleoptera: Coccinellidae) in Different Habitats in Maine

Abstract Several studies suggest the possibility that non-native lady beetles may have replaced native lady beetles in some agricultural habitats. There is relatively little information, however, about lady beetle species composition outside of agricultural habitats. Evans (2004) suggested that native species have retreated to nonagricultural habitats in response to the arrival of non-native lady beetles (habitat compression hypothesis). To test this hypothesis, a survey of lady beetles was conducted in 2004 and 2005 in different habitats in Maine. From May to October, lady beetles were sampled in a variety of agricultural and nonagricultural habitats. In total, 3,487 and 2,903 lady beetles were collected in 2004 and 2005, respectively. Non-native lady beetles were found in a variety of habitats, including the habitats that would have likely served as a refuge for native species if the habitat compression hypothesis applied to the surveyed areas. Native species were found in a higher proportion in agricultural habitats compared with nonagricultural habitats and in very low numbers in all of the habitats surveyed. Hippodamia tredecimpunctata tibialis (Say) and Coccinella transversoguttata Brown, the two native species that were once dominant here, made up only 1.09 and 0.07% of the total lady beetles collected, respectively. In this survey, we failed to detect evidence that native lady beetles have retreated to nonagricultural habitats in response to the arrival of non-native lady beetles.

Differential Consumption of Four Aphid Species by Four Lady Beetle Species

Abstract The acceptability of four different aphid species Macrosiphum albifrons (Essig), Macrosiphum euphorbiae (Thomas), Macrosiphum pseudorosae Patch, and Myzus persicae (Sulzer) (Hemiptera: Aphididae), as prey for four lady beetle species, one native species Coccinella trifasciata L, and three non-native Coccinella septempunctata L, Harmonia axyridis Pallas, Propylea quatuordecimpunctata L (Coleoptera: Coccinellidae) were tested in the laboratory. The relative field abundance of adults of the same lady beetle species on host vegetation, Lupinus polyphyllus Lindley (Fabales: Fabaceae), Solanum tuberosum L (Solanales: Solanaceae), and Rosa multiflora Thunberg (Rosales: Rosaceae), both with and without aphids present was also observed. In the laboratory, H. axyridis generally consumed the most aphids, while P. quatuordecimpunctata consumed the fewest. The exception was P. quatuordecimpunctata, which consumed a greater number of M. albifrons nymphs, and C. trifasciata, which consumed a greater number of M. albifrons nymphs and adults, compared with the other two beetle species. Lady beetles consumed fewer M. albifrons compared with the other three aphid species, likely because of deterrent compounds sequestered by this species from its host plant. In the field, P. quatuordecimpunctata was the most abundant species found on L. polyphyllus and S. tuberosum.

Reduced Fitness of the Colorado Potato Beetle (Coleoptera: Chrysomelidae) on Potato Plants Grown in Manure-amended Soil

Abstract Colorado potato beetle, Leptinotarsa decemlineata (Say), is the most important insect defoliator of potatoes worldwide. In this study, we conducted a series of no-choice assays comparing Colorado potato beetle reproduction and development on potato plants grown in manure-amended and synthetically fertilized soils. Manure-amended soil received annual applications of raw cow manure since 1991 and additional applications of cull potato compost and green manure between 1991 and 1998. Plants grown in manure-amended soil were inferior Colorado potato beetle hosts compared with plants grown in synthetically fertilized soil. The observed negative effects were broad in scope. Female fecundity was lower in field cages set up on manure-amended plots early in the season, although it later became comparable between the treatments. Fewer larvae survived past the first instar, and development of immature stages was slowed down on manure-amended plots. In the laboratory, first instars consumed less foliage from plants grown in manure-amended soils. These results show that organic soil management is associated with plant characteristics unfavorable for beetle reproduction and development, which should be taken into consideration when designing fully integrated crop management systems.

Current status of insecticidal control of wireworms in potatoes

Thomas P. Kuhar (Department of Entomology, Virginia Tech), John Speese III (Eastern Shore Agricultural Research and Extension Center, Virginia Tech), Joanne Whalen (Department of Entomology and Applied Ecology, University of Delaware), Juan M. Alvarez (Department of Plant, Soil and Entomological Sciences, University of Idaho), Andrei Alyokhin (Department of Biology, University of Maine), Gerald Ghidiu (Department of Entomology, Rutgers University) and Martin R. Spellman (Extension IPM Associate, University of Delaware) summarize the performance of various insecticides in efficacy trials for control of wireworms in potatoes and discuss the future outlook.