North-Western Journal of Zoology Vol. 6, No. 1, 2010, pp.54-62 P-ISSN: 1584-9074, E-ISSN: 1843-5629 Article No.: 061106 Measuring pear psylla population density (Cacopsylla pyri L. and C. pyricola Förster): review of previous methods and evaluation of a new technique Gábor JENSER1, Éva SZITA1* and János BÁLINT2 1. Plant Protection Institute of Hungarian Academy of Sciences, P.O. Box 102 H-1525 Budapest Hungary. 2. Department of Horticulture, Sapientia University, Faculty of Technical and Human Sciences, 1/c Shigisoarei st. Tirgu-Mures, Romania. * Corresponding author: É. Szita, Plant Protection Institute of Hungarian Academy of Sciences, P.O. Box 102 H-1525 Budapest Hungary, E-mail: [email protected] Abstract. Following the survey of the proposed and applied methods the wash-down procedure has been evaluated to collect the pear psylla larvae (Cacopsylla pyri Linnaeus and C. pyricola Förster) in order to establish their population density. To select the larvae the shoots or flowers should be washed-down by water containing 1% detergent. To concentrate larvae, the detergent solution was strained through filter paper. After that it is possible to count exactly the number of larvae by using dissection microscope. By this way the total number of the developing larvae occurring in the flowers or on the shoots could be established. By the application of this method, it is possible to obtain real data about the absolute population density and its changes, as well as the susceptibility or tolerance of the pear cultivars to pear psylla. The data provided by the wash-down method was compared with the traditional limb beating method. Keywords: methodology, wash-down method, absolute density estimation, Cacopsylla pyri, Cacopsylla pyricola Introduction the most dangerous species in North America (Alston & Murray 2007, Horton 1994, Horton et High psylla population densities in pear orch- al. 1992) and in Great Britain (Hodgson & ards have been reported over many decades in Mustafa 1984, Solomon et al. 1989). Mixed Europe, with the first outbreaks occurring in populations of these species were reported the early 1950s in France (Bonnemaison & from The Netherlands (Trapman & Blommers Missonnier 1955, 1956). Psylla infestation is the 1992, Van der Blom et al. 1985). These two most important pest management problem of species are almost equal in size and have pear-growing districts in Europe (Geoffrion similar life strategies. The reasons of its high 1984, Gobin et al. 2005, Jenser 1988, Pasqualini population density and the possibilities of the et al. 2003, Erler 2004b). prevention of damage are studied since that Two Psylla species have caused severe time. The development of control strategies, economic damage in pear orchards since the effects of insecticides, causes of insecticide beginning of commercial pear production. resistance, role of the predators in population While Cacopsylla pyri (Linneaus, 1758) is the dynamics, and the effect of phytotechnique main pest in most of Europe (Berrada et al. (Atger & Lemoine 1984, Brunner 1984, Pfeiffer 1996, Civolani & Pasqualini 2003, Erler et al. & Burts 1983, Westigard et al. 1980) were 2007, Jenser 1988), C. pyricola (Förster, 1848) is investigated continuously, and the individual ©NwjZ, Oradea, Romania, 2010 North-West J Zool, 6, 2010 www.herp-or.uv.ro/nwjz Oradea, Romania Pear psylla collecting methods 55 number or the changes of the population den- during a relatively short time. These can be sities have been established by the different distinguished from methodological point of methods. view by the dimension of collecting tools, This paper presents a review of the which can be two- and three-dimensional. methods used for collecting pear psyllids. A Two-dimensional methods: beating tray methods. description of the wash-down method is The two-dimensional collecting tool is a textile presented, along with a comparison with the sheet stretched on a rectangular or round traditional limb-beating method. frame, called beating tray or frappage. The white textile-covered tray is held beneath a tree Review of the methods for determining pear limb, and the limb is hit three times with a psylla population density (Cacopsylla pyri and rubber hose. Dislodged psylla and other ani- C. pyricola) mals which fell on the tray are counted or Yellow sticky-board trap for pear psylla detection collected by aspirator immediately in the was developed by Kaloostian and Yeomans in orchard. 1944 (Kaloostian 1961). This method was Authors used beating trays in large variety examined and estimated by several authors of size and shape. Burts and Retan (1973) (Adams & Los 1989, Horton 1993, Kaloostian developed the most widespread beating tray 1961, Krysan & Horton 1991, Brown et al. type which is 45 x 45 cm (18 x 18 inch; area ~ 2009). Significant differences were established 0.2 m2) in size. This procedure was applied by by Adams and Los (1989) regarding the several authors (Burts & Brunner 1981, Daniel effectiveness of yellow sticky traps placed at & Wyss 2004, Deronzier 1984, Erler 2004b, different heights, orientations and quadrants of Horton 1994, 1993, 1994, Horton et al. 1992, pear trees. Hue and intensity of reflection 2008, Krysan & Horton 1991, Paulson & Akre appear to be important for eliciting positive 1992, Pfeiffer & Burts 1983, Stratopoulou & reflection response by pear psylla adults to Kapatos 1995, Westigard & Moffitt 1984). visual traps. The greatest captures occurred for Alston and co-workers (Alston & Murray 2007, hues with reflection peaks in the 520 to 600-nm Alston & Reding 1998, 2003) published a pesti- range of the spectrum (Adams et al. 1983). cide program against pear psylla for farming Seasonality of the catch and flight activity of practice: 0.2 adult psylla/tray was suggested as pear psylla (C. pyricola) was observed by treatment threshold under monitoring of psylla several authors (Civolani & Pasqualini 2003, population with Burts and Retan’s (1973) Erler 2004b, Horton 1994, Krysan & Horton beating tray method. Beating tray with 0.25 m2 1991), and diurnal difference was reported by area was used by several authors as well (Horton 1993). Intraorchard changes in distri- (Deronzier 1984, Rieux & D'Arcier 1983, Rieux bution associated with leaf fall were investi- et al. 1992, Trapman & Blommers 1992). Herard gated by Horton et al. (1993). Reduced catch (1985, 1986), Herard and Chen (1985), Miliczky can be observed under cool weather conditions (2005) and Brown et al. (2009) applied 0.5 m2 (Horton 1994). tray in their surveys. Some researchers used beating trays with unique size: Civolani and Limb beating or limb jarring to collect arthropod Pasqualini (2003) used 55 cm x 25 cm (area ~ specimens from trees and shrubs has been 0.14 m2) frappage in Italy, Severin and co- known for a long time and in several varia- workers (1984) applied 40 cm x 40 cm (area tions. It is possible to take a high number of 0.16 m2) sized one in France, while Santas samples and to establish the density of psylla (1987) in Greece worked with 1 m x 1 m (area 1 adults and other insects with these methods m2) sized beating tray. The authenticity of the North-West J Zool, 6, 2010 56 Jenser, G. et al. data provided by this type of method depends (1995), Jenser et al. (2009) and the second considerably on weather condition. When author of the present paper. temperature increases, most of the adults fly Both the application of the sticky board away (Deronzier & Atger 1980). Therefore it is traps and beating tray provide accurate infor- necessary to take the sample in the morning mation about the changes of pear psylla popu- (Deronzier & Atger 1980, Erler 2004b, Horton lation density. A few of the authors provide 1994). information on the correlation of catch data of different collecting methods. Adams and Los Three-dimensional methods: beating umbrella (1989) concluded that Lightning Yellow and methods. Using three-dimensional limb beating Arc Yellow sticky traps were more highly and methods the dislodged insects fall into a more consistently correlated with the occur- funnel-like structure instead of a flat sheet. rence of pear psylla eggs and nymphs on pear This funnel-like structure is often called spurs and sooty mold blemishing on fruit than “beating umbrella”. Due to its vertical exten- were counts obtained by beating tray. In the sion, this method is much less temperature- investigations of Krysan and Horton (1991) and wind-sensitive and much more suitable for correlations between trap catches and beating collecting fast moving or flying beneficial tray numbers tended to be non-significant, organisms (e.g. spiders, pirate bugs) than the while Horton (1994) found it to be significant. two-dimensional methods mentioned above. The amount of collected insects generally The psylla eggs were counted on the shoots and makes necessary the laboratory process. leaves using a binocular dissecting microscope Steiner (1962) investigated the arthropod by Jenser (1988), Adams and Los (1989), populations occurring in the orchards, used a Stratopoulou and Kapatos (1995), Erler (2004c), plastic funnel with an aperture of 0.25 m2 Erler and Cetin (2005, 2007) and Erler et al. instead of textile umbrella. A glass vessel of (2007). A few of the authors investigated and 335 cm3 was used for gathering the specimens counted both the eggs and larvae (Brunner at the bottom of the funnel. Fauvel et al. (1981) 1984, Pasqualini et al. 2003, Scutareanu et al. used the same technique, they filled the 1999, Mari et al. 2009). Counting the eggs and gathering vessel with a small amount of 70% larvae on the shoots provides real data, but the alcohol. Rieaux (1999) mentioned this method sample must be taken into the laboratory and it above as “Fauvel’s funnel method”. Bouyjou et is necessary to complete the counting within a al. (1984) used this technique for predator and short time.