1. Identification of the pear psyllids specimen as potential vectors of ‘Candidatus Phytoplasma pyri’ on the territory of Canton of Geneva, Switzerland
Aneliya Etropolska and François Lefort.
Plants and pathogens group, in TNE, hepia, University of Applied Science and Arts Western Switzerland, Route de Presinge 150, 1254 Jussy, Geneva, Switzerland.
The pear psyllids from genus Cacopsylla (fam. Psyllidae) are one of the most economic important pests, which have been reported to feed on Pyrus spp. They cause direct damages – by feeding from the phloem of the trees and indirect damages - by secreting a honeydew on all parts of the tree including the fruits. Later the honeydew is used from black sooty funguses as a growing media. Some of the Cacopsylla species are known to transmit the phytoplasma ‘Candidatus Phytoplasma pyri’, the agent of Pear decline (PD). The species Cacopsylla pyri is the main proven PD-vector in several European countries. There are records that the psyllid Cacopsylla pyricola is also a PD-vector in some regions. Two other species, Cacopsylla pyrisuga and Cacopsylla bidens were found to be infected, but they were never confirmed as vectors through transmission’s trails, therefore only known as putative vectors.
In Europe, PD is considered as one of the most damaging disease on pear, which caused significant losses in the main pear-growing regions. Eradication of all infected plants and chemical treatments against the vector, are the only way to minimize the spread of the disease, although that the pear psyllids developed a high resistance to pesticides in the last 20 years. Other very common problem is that pesticides are used without a correct identification of the pear psyllids. On the territory of Canton of Geneva, the determination and the distribution of PD-disease and their possible vector/s were not studied in detail so far.
Microscope preparation of genitalia of ♂ and ♀ pear psyllids
Additionally microscope slides of genitalia of male and female individuals were prepared.
C. pyricola
C. pyri
C. pyrisuga
Fig. 3. Parameres of male pear psyllids.
Fig. 5. Microscope preparation of genitalia of ♂ and ♀ of Cacopsylla pyri.
Material and methods
At the beginning of Spring 2017, a regular monitoring of the pear psyllids was conducted in several biological and conventional pear orchards on the territory of Canton of Geneva. Psyllids (winter form), as well as individuals from the summer generation were collected, using the beating tray method, from 5 different orchards located in Jussy, Choulex, and Collonge-Bellerive. Further morphological identification was conducted using several determination keys.
Fig. 6. Microscope preparation of genitalia of ♂ and ♀ of Cacopsylla pyricola.
Results
Fig. 7. Microscope preparation of genitalia of ♂ and ♀ of Cacopsylla pyrisuga. .
In total, 393 individuals from the genus Cacopsylla spp. were trapped on pear and later determined.
The most common species was C. pyri (200 individuals), found mainly in the two orchards in Jussy. As a contrast, the second most common species C. pyricola (127 individuals) was found mainly in Collonge-Bellerive and only few individuals in Choulex and Jussy. In general, the third species C. pyrisuga was less present (66 individuals) and always found in mixed populations with the other two species.
Morphological identification of the potential vectors of ‘Candidatus Phytoplasma pyri’
The psyllids belonged to three species: C. pyri, C. pyricola and C. pyrisuga. In some causes they have been found together in the pear orchards, which fact makes the identification and the morphological distinguishing very difficult. (Figure 1).
Discussion
In the future, all captured psyllids will be analyzed for possible PD- infection and new specific primers for confirmation of each species will be validated. In case that some individuals will be found to be infected, further observations for PD - symptoms and plant sampling will be carried out in Autumn 2017.
Fig. 1. Mixed populations of C. pyri, C. pyricola and C. pyrisuga
For separating the species of pear psyllids the male and female terminalia have to be examined (Figures: 2; 3; 4).
References
Burckhardt et al.,
2. Hodkinson, I.,D., White, I.,M Homoptera: Psylloidea. Handbook for the Identification of British Insects 2(5a): 1-98.
3. Hodkinson, I.,D., The taxonomy, distribution and host-plant range of the pear feeding psyllids. Bulletins 7: 32-44
4. Loginova M Насекомые и клещи - вредители сельскохозяйственных культур. Наука. Т.1. Насекомые с неполным превращением
5 . Ossiannilsson F., Fauna Entomologica Scandinavica, 29: 1-346
6 . Valle et al., Check List, 13 (2), article 2088: 1-4.
Fig. 2 C. pyri (♀ and ♂)
Fig. 3 C. pyricola (♀and ♂)
Fig. 4 C. pyrisuga (♀and ♂)
Pictures used: Etropolska A., Burckhard D.
JOURNEES D'AUTOMNE SGP / SSP 2017
Diagnostique en phytiatrie: clé du succès en protection des plantes?
8-9 septembre 2017, hepia, Genève