Citrus mealybug (Hemiptera: Pseudococcidae) movement and population dynamics in an arbor-trained vineyard

A Novel Insect Overwintering Strategy: The Case of Mealybugs

Insects have limited ability to regulate their body temperature and have thus required a range of strategies to withstand thermally stressful environments. Under unfavorable winter conditions, insects often take refuge under the soil surface to survive. Here, the mealybug insect family was selected for the study. Field experiments were performed in fruit orchards in eastern Spain. We used specifically designed floor sampling methods combined with fruit tree canopy pheromone traps. We found that in temperate climates, the large majority of the mealybugs move from the tree canopy to the roots during the winter, where they turn into belowground root-feeding herbivores to survive and continue underground the reproductive process. Within the rhizosphere, mealybugs complete at least one generation before emerging on the soil surface. The preferred area to overwinter is within 1 m in diameter around the fruit tree trunk, where more than 12,000 mealybug flying males per square meter can emerge every spring. This overwintering pattern has not previously been reported for any other group of insects showing cold avoidance behavior. These findings have implications at the winter ecology level but also at the agronomical level since treatments to control mealybug pests are, until now, only based on the fruit trees' canopy.

Temperature Thresholds and Thermal Requirements for Development and Survival of Dysmicoccus brevipes (Hemiptera: Pseudococcidae) on Table Grapes

Temperature is an important climate factor that has a direct influence on insect biology and consequently a crucial role in forecasting and integrated pest management. The mealybug Dysmicoccus brevipes (Cockerell) (Hemiptera: Pseudococcidae) is one of the most common species in Brazilian vineyards. Here, development and survival of D. brevipes on leaves of table grapes (Vitis vinifera cv. Itália) were studied at five constant temperatures (15, 20, 25, 28, and 30 ± 1°C) under laboratory conditions. We investigated the developmental time and nymphal survival, temperature thresholds, and the degree-day requirements for each life stage of D. brevipes. The developmental time for the nymphal stage ranged from 32 to 130 days with decreasing the temperature, with the temperatures of 28 and 30°C providing the shorter developmental time. Survival of the entire nymphal stage was affected by the temperature, ranging from 81% at 20°C to 1% at 15°C. The predicted upper lethal temperature was 34.5°C, while the optimal temperature was 28.6°C. The minimum threshold for total development of D. brevipes occurred at 8.2°C. Dysmicoccus brevipes required 678.4 degree-days to complete development from first-instar nymph to adult. The temperature of 30°C was the most suitable for the development of D. brevipes. The thermal thresholds estimated for D. brevipes life cycle suggest that this species can develop in different table grape-producing regions of Brazil, in a temperature range between 8 and 35°C.

Seasonal Distribution and Movement of the Invasive Pest Delottococcus aberiae (Hemiptera: Pseudococcidae) Within Citrus Tree: Implications for Its Integrated Management

Delottococcus aberiae (De Lotto) (Hemiptera: Pseudococcidae) is the most recent species of mealybug introduced to Spain that is affecting citrus. The feeding behavior of D. aberiae causes severe direct damage to citrus fruits, distorting their shape and/or causing reduction in size. There is no information available regarding its distribution within the citrus trees. The main objective of this study was to describe the seasonal distribution of D. aberiae within citrus trees and its migration patterns on the plants. Ten citrus orchards from eastern Spain were periodically sampled during 3 yr. In each orchard, the mealybug was sampled in different infested strata (canopy, trunk, and soil) and canopy structures (flower, fruit, leaf, and twig). Results showed that, within the sampled strata, D. aberiae was mostly in the canopy. Within the canopy, the feeding location of D. aberiae changed throughout the year. D. aberiae overwintered in the twigs and moved to the flowers and fruits in spring. Once there, its populations started to increase exponentially until August. From February to September, 5-30% of the mealybugs migrated to the trunk and soil. These results will facilitate an early detection of the pest in the areas where it is spreading and improve sampling protocols and pesticide applications.

Profiling viral infections in grapevine using a randomly primed reverse transcription-polymerase chain reaction/macroarray multiplex platform

Crop-specific diagnostics to simultaneously detect a large number of pathogens provides an invaluable platform for the screening of vegetative material prior to its propagation. Here we report the use of what is to-date the largest published example of a crop-specific macroarray for the detection of 38 of the most prevalent or emergent viruses to infect grapevine. The reusable array consists of 1,578 virus-specific 60 to 70mer oligonucleotide probes and 19 plant and internal control probes spotted onto an 18 × 7 cm nylon membrane. In a survey of 99 grapevines from the United States and Europe, virus infections were detected in 46 selections of Vitis vinifera, V. labrusca, and interspecific hybrids. The majority of infected vines (30) was singly infected, while 16 were mixed-infected with viruses from two or more families. Representatives of the four main virus families Betaflexiviridae, Closteroviridae, Secoviridae, and Tymoviridae present in grapevines were found alone and in combination, with a notable bias in representation by members of the family Tymoviridae. This work demonstrates the utility of the macroarray platform for the multiplex detection of viruses in a single crop, its potential for characterizing grapevine virus associations, and usefulness for rapid diagnostics of introduced material in quarantine centers or in certification programs.

Ecology and management of grapevine leafroll disease

Grapevine leafroll disease (GLD) is caused by a complex of vector-borne virus species in the family Closteroviridae. GLD is present in all grape-growing regions of the world, primarily affecting wine grape varieties. The disease has emerged in the last two decades as one of the major factors affecting grape fruit quality, leading to research efforts aimed at reducing its economic impact. Most research has focused on the pathogens themselves, such as improved detection protocols, with limited work directed toward disease ecology and the development of management practices. Here we discuss the ecology and management of GLD, focusing primarily on Grapevine leafroll-associated virus 3, the most important virus species within the complex. We contextualize research done on this system within an ecological framework that forms the backbone of the discussion regarding current and potential GLD management strategies. To reach this goal, we introduce various aspects of GLD biology and ecology, followed by disease management case studies from four different countries and continents (South Africa, New Zealand, California-USA, and France). We review ongoing regional efforts that serve as models for improved strategies to control this economically important and worldwide disease, highlighting scientific gaps that must be filled for the development of knowledge-based sustainable GLD management practices.

Development of a multiplex PCR for identification of vineyard mealybugs

A simple molecular tool was developed and tested to identify seven mealybug species found in North American vineyards: Pseudococcus maritimus Ehrhorn, Pseudococcus viburni (Signoret), Pseudococcus longispinus (Targioni-Tozzeti), Pseudococcus calceolariae (Maskell), Planococcus ficus (Signoret), Planococcus citri (Risso), and Ferrisia gilli Gullan. The developed multiplex PCR is based on the mitochondrial cytochrome c oxidase subunit one gene. In tests, this single-step multiplex PCR correctly identified 95 of 95 mealybug samples, representing all seven species and collected from diverse geographic regions. To test the sensitivity, single specimen samples with different Pl. ficus developmental stages (egg to adult female and adult male) were processed PCR and the resulting output provided consistent positive identification. To test the utility of this protocol for adult males caught in sex baited pheromone traps, Pl. ficus adult males were placed in pheromone traps, aged at a constant temperature of 26±2°C, and processed with the multiplex each day thereafter for 8 d. Results showed consistent positive identification for up to 6 d (range, 6-8 d). Results are discussed with respect to the usefulness of this molecular tool for the identification of mealybugs in pest management programs and biosecurity of invasive mealybugs.