Probing behaviour of Cacopsylla pyri on a resistant pear selection

Abstract

European pear psylla Cacopsylla pyri L. (Hemiptera Psyllidae) is one of the worst pests of pear (Pyrus communis L.) in Europe. We investigated probing behaviour in adults and nymphs of C. pyri by full EPG on a psylla‐resistant pear selection, NY 10353. Concerning stylet probing behaviour on the plant surface, the results showed no significant differences between the resistant selection and the susceptible cultivar Bartlett, and no differences were also detected for epidermis and mesophyll resistance in the same conditions. For mesophyll/phloem, no differences were found in adults. However, in nymphs, weak resistance factors (longer stylet penetration and mesophyll salivation) were detected in the resistant selection. In phloem, EPG data indicate strong resistance factors in NY 10353, especially for nymphs and summer‐form adults (longer time before the first phloem ingestion and a lower duration of each phloem ingestion event). No prolonged (>10 min) phloem ingestion was performed by nymphs and adults in the resistant selection. The results support the hypothesis that NY 10353 resistance factors are located in the phloem sap and cause high C. pyri nymph mortality: this could be useful as a basis for further investigations of resistance mechanisms at the metabolic, chemical and genetic levels.

Differences in Stylet Sheath Occurrence and the Fibrous Ring (Sclerenchyma) between xCitroncirus Plants Relatively Resistant or Susceptible to Adults of the Asian Citrus Psyllid Diaphorina citri (Hemiptera: Liviidae)

“…However, other factors may contribute to insect resistance in plants even when the stylets have reached the phloem. Nymphs and adults of the European pear psylla ( Cacopsylla pyri L.) do not ingest from the phloem in resistant selections of pear for any prolonged period, which suggests that resistance factors are located in the phloem sap rather than factors outside the phloem [26] . Factors inside and outside the phloem seem to be involved with resistance to the soybean aphid, Aphis glycines Matsumura where EPG studies showed the following: a. soybean aphids feeding on susceptible genotypes had a significantly greater duration of sieve element phase than when feeding on resistant genotypes, b. the time taken to reach the first sieve element phase in resistant genotypes was significantly greater than in susceptible ones, and c. most of the aphids reached sieve element phase in susceptible genotypes but only a few reached this phase in resistant genotypes [27] .…”

Field evaluation of the relative susceptibility of six pear varieties to the pear psylla (Cacopsylla pyricola (Foerster, 1848))

“…Resistance of deciduous plants to phloem feeding insects is supposed to result from a combination of structural and excited physical and chemical guards (Eyles et al, 2007). Host resistance has long been regarded as the best alternative and ecologically secure outlook to chemical control of pear psyllid (Civolani et al, 2013). Some of these varieties may be exploited in organic farming combined with biological control.…”

Two pear accessions evaluated for susceptibility to pear psyllaCacopsylla bidens(Šulc) in Israel

“…Other studies support the hypothesis that the resistance factors that cause high C. piri nymph mortality are located in the phloem. For example, a recent electrical penetration graph study found for C. piri nymphs and summer‐form adults, a longer time before the first phloem ingestion, and a lower duration of each phloem ingestion event, on the resistant hybrid pear selection NY10355, than on the susceptible cultivar Bartlett . Another study based on the resistant selection NY10355 found that psylla resistance was not very well transmitted, indicating that genetic architecture of psylla resistance in NY10355 results either from a combination of several small‐effect resistance genes or from a combination of either dominance or epistatic effects or from both .…”