Retention and Transmission of Grapevine Leafroll-Associated Virus 3 by Pseudococcus calceolariae

Grapevine leafroll-associated virus 3 (GLRaV-3), an economically significant pathogen of grapevines, is transmitted by Pseudococcus calceolariae, a mealybug commonly found in New Zealand vineyards. To help inform alternative GLRaV-3 control strategies, this study evaluated the three-way interaction between the mealybug, its plant host and the virus. The retention and transmission of GLRaV-3 by P. calceolariae after access to non-Vitis host plants (and a non-GLRaV-3 host) White clover (Trifolium repens L. cv. “Grasslands Huia white clover”), Crimson clover (T. incarnatum), and Nicotiana benthamiana (an alternative GLRaV-3 host) was investigated. For all experiments, P. calceolariae first instars with a 4 or 6 days acquisition access period on GLRaV-3-positive grapevine leaves were used. GLRaV-3 was detected in mealybugs up to 16 days on non-Vitis plant hosts but not after 20 days. GLRaV-3 was retained by second instars (n = 8/45) and exuviae (molted skin, n = 6/6) following a 4 days acquisition period on infected grapevines leaves and an 11 days feeding on non-Vitis plant hosts. Furthermore, GLRaV-3 was transmitted to grapevine (40−60%) by P. calceolariae second instars after access to white clover for up to 11 days; 90% transmission to grapevine was achieved when no alternative host feeding was provided. The 16 days retention period is the longest observed in mealybug vectoring of GLRaV-3. The results suggest that an alternative strategy of using ground-cover plants as a disrupter of virus transmission may be effective if mealybugs settle and continue to feed on them for 20 or more days.

Mating Disruption of Pseudococcus calceolariae (Maskell) (Hemiptera, Pseudococcidae) in Fruit Crops

Pseudococcus calceolariae, the citrophilous mealybug, is a species of economic importance. Mating disruption (MD) is a potential control tool. During 2017–2020, trials were conducted to evaluate the potential of P. calceolariae MD in an apple and a tangerine orchard. Two pheromone doses, 6.32 g/ha (2017–2018) and 9.45 g/ha (2019–2020), were tested. The intermediate season (2018–2019) was evaluated without pheromone renewal to study the persistence of the pheromone effect. Male captures in pheromone traps, mealybug population/plant, percentage of infested fruit at harvest and mating disruption index (MDI) were recorded regularly. In both orchards, in the first season, male captures were significantly lower in MD plots compared to control plots, with an MDI > 94% in the first month after pheromone deployment. During the second season, significantly lower male captures in MD plots were still observed, with an average MDI of 80%. At the third season, male captures were again significant lower in MD than control plots shortly after pheromone applications. In both orchards, population by visual inspection and infested fruits were very low, without differences between MD and control plots. These results show the potential use of mating disruption for the control of P. calceolariae.

The management and financial implications of variable responses to grapevine leafroll disease

© 2021, Società Italiana di Patologia Vegetale (S.I.Pa.V.). Grapevine leafroll-associated virus 3 (GLRaV-3) is a worldwide pathogen of Vitis negatively affecting wine production. In red berry cultivars grown in New Zealand, the foliar changes to GLRaV-3-infected vines inform decisions on vine removal (roguing). However, roguing does not always contain GLRaV-3 spread in the presence of an insect vector like the mealybug, Pseudococcus calceolariae. Virus incidence and mealybug abundance data collected annually over 7 years were modelled under differing scenarios to ascertain support for roguing. In a simulated 1 ha vineyard planted in 2500 mature Merlot vines, simulations over 20 years evaluated the effectiveness of roguing, ‘rogue 1 + 2’ (concurrent roguing of symptomatic plus both within-row neighbouring vines), inefficient roguing (50% of symptomatic vines rogued), and ‘no-action’. The model used variable initial GLRaV-3 incidence (0.4, 5, 10, 15 and 20%), and low, median and high vector densities (6, 26 and 75 mealybugs per 100 vine leaves, respectively). Roguing was the optimal response to GLRaV-3, independent of the initial incidence, but results were vector density dependent. At a low vector density, roguing relative to the other responses tested, sustained the lowest annual GLRaV-3 incidence, the least need to plant replacement vines and the lowest estimated average annual costs plus loss of income. At median and high vector densities, roguing remained the most favourable response but virus control was less effective and the costs incurred were higher. Thus, for vineyards affected by GLRaV-3, achieving economic sustainability relies on integrating efficient roguing with effective vector management.

The management and financial implications of variable responses to grapevine leafroll disease

© 2021, Società Italiana di Patologia Vegetale (S.I.Pa.V.). Grapevine leafroll-associated virus 3 (GLRaV-3) is a worldwide pathogen of Vitis negatively affecting wine production. In red berry cultivars grown in New Zealand, the foliar changes to GLRaV-3-infected vines inform decisions on vine removal (roguing). However, roguing does not always contain GLRaV-3 spread in the presence of an insect vector like the mealybug, Pseudococcus calceolariae. Virus incidence and mealybug abundance data collected annually over 7 years were modelled under differing scenarios to ascertain support for roguing. In a simulated 1 ha vineyard planted in 2500 mature Merlot vines, simulations over 20 years evaluated the effectiveness of roguing, ‘rogue 1 + 2’ (concurrent roguing of symptomatic plus both within-row neighbouring vines), inefficient roguing (50% of symptomatic vines rogued), and ‘no-action’. The model used variable initial GLRaV-3 incidence (0.4, 5, 10, 15 and 20%), and low, median and high vector densities (6, 26 and 75 mealybugs per 100 vine leaves, respectively). Roguing was the optimal response to GLRaV-3, independent of the initial incidence, but results were vector density dependent. At a low vector density, roguing relative to the other responses tested, sustained the lowest annual GLRaV-3 incidence, the least need to plant replacement vines and the lowest estimated average annual costs plus loss of income. At median and high vector densities, roguing remained the most favourable response but virus control was less effective and the costs incurred were higher. Thus, for vineyards affected by GLRaV-3, achieving economic sustainability relies on integrating efficient roguing with effective vector management.

Multiple Mating in the Citrophilous Mealybug Pseudococcus calceolariae: Implications for Mating Disruption

The citrophilous mealybug Pseudococcus calceolariae (Maskell) (Hemiptera, Pseudococcidae) is a primary pest of various crops, including grapevines. The use of insecticides against this species is difficult in most cases because its life cycle includes an extended duration of eggs, juveniles, and adults under the bark and on the roots. Pheromone-based control strategies can present new eco-friendly opportunities to manage this species, as in the case of Planococcus ficus (Signoret) and Planococcus citri (Risso). With this aim it is critical to understand behavioral aspects that may influence pheromone-based control strategies. Herein, the capability of males to fertilize multiple females was investigated, trying to understand whether this behavior could negatively impact the efficacy of mass trapping, mating disruption, or the lure and kill technique. Results showed that a P. calceolariae male can successfully mate and fertilize up to 13 females. The copulation time in subsequent mating events and the time between copulations did not change over time but the number of matings per day significantly decreased. In a further experiment, we investigated the mate location strategy of P. calceolariae males, testing the attractiveness of different loadings of sex pheromone on males in a flight tunnel. Males constantly exposed to 16 rubber septa loaded with the sex pheromone showed a significant decrease in female detection at 1 and 30 μg loadings (0.18 and 0.74 visits per female for each visit per septum, respectively), whereas in the control about 9.2-fold more of the released males successfully detected the female in the center of the array of 16 septa without pheromone. Male location of females in the control (45%) was significantly higher than in the arrays with surrounding pheromone (5% and 20% at 1 and 30 μg loadings, respectively). Mating only occurred in the control arrays (45%). This study represents a useful first step to developing pheromone-based strategies for the control of citrophilous mealybugs.

Mealybug preference among clover cultivars: testing potential groundcover plants to dissociate mealybugs from grapevines

The choice of groundcover plants used under grapevines may reduce the quantity of mealybugs found on grapevines in New Zealand vineyards. Preferences of Pseudococcus calceolariae and P. longispinus mealybugs on five clover cultivars were tested under ‘no-choice’ and ‘choice’ conditions. Two plants of each cultivar: ‘Karridale’(KS) (Trifolium subterraneum, L.), ‘Tripoli’ (TW), ‘Nomad’ (N) (T. repens), ‘Crimson cv’ (C) (T. incarnatum) and ‘Strawberry cv’ (S) (T. fragiferum) grown in pots, were arranged in randomised designs for the no-choice and choice tests and inoculated with newly emerged mealybugs. In the no-choice test, significantly more mealybugs (either species) were observed on KS and C than on TW, N, or S plants after 21 days. In the choice test, significantly more P. calceolariae were observed on KS than on TW, N, or S, while mealybug numbers on C were intermediate. Numbers of P. longispinus were significantly higher on KS and C than on TW, N or S. Mealybugs demonstrated preferences for KS and C over TW, N or S. These findings could aid development of recommendations for groundcover management in vineyards.

Scale insects (Hemiptera: Coccomorpha) on sugarcane in Colombia, with description of a new species of Tillancoccus Ben-Dov (Coccidae)

Herein we describe a new species, Tillancoccus koreguajae Caballero & Ramos, sp. n. (Hemiptera: Coccidae) from Colombia collected on sugarcane. Pinnaspis strachani (Cooley) is also recorded on sugarcane for the first time worldwide. An updated list of seven species of Coccomorpha on sugarcane in Colombia is provided, including information on its distribution, biology, and mutualistic ants for each species. Seven species of scale insects (Hemiptera: Coccomorpha) have been recorded previously on sugarcane, Saccharum officinarum L. (Poaceae) in Colombia: Pseudococcidae: Dysmicoccus boninsis (Kuwana), D. brevipes (Cockerell), Pseudococcus calceolariae (Maskell), Saccharicoccus sacchari (Cockerell); Coccidae: Pulvinaria elongata Newstead; Diaspididae: Duplachionaspis divergens (Green) and Serenaspis minima (Maskell). However, the record of S. minima in Colombia is considered doubtful as there are no voucher specimens from Colombia and because the distribution of this species is currently limited to the Australasian region. Pseudococcus calceolariae is present in Colombia but its record on sugarcane is also doubtful. A taxonomic key for the identification of scale insects on sugarcane in Colombia is provided.

Development of citrophilus mealybug (Pseudococcus calceolariae) on grape roots

Pseudococcus calceolariae (Hemiptera Pseudococcidae) is a vector of Grapevine leafrollassociated virus 3 (GLRaV3) the most destructive virus disease affecting New Zealand grapevines Previous studies suggest that P calceolariae can survive on remnant vine roots for at least 12 months and these mealybugs could account for the spread of the disease in replanted vineyards A laboratory assay test was developed to observe the growth of P calceolariae on grape rootstock 3309 Clean root pieces were left on moist filter paper in Petri dishes for a week to encourage new growth before P calceolariae eggs (n15) were inoculated and held at 23C Recordings were made every 34 days of the survival and development from first instar until males emerged as adults and females started oviposition About 50 mortality was recorded during first and second instars and ca 30 developed into adult stages The development periods from first instar to adult males and females were 441 1 (n16) and 454 1 (n22) respectively This methodology is being developed to assess the relative resistance of grapevine rootstocks effects of contact insecticides and to understand GLRaV3 transmission from roots