# Larval development of Cacopsylla pyri (L.) [Homoptera: Psyllidae] on two resistant Pyrus genotypes

Philippe Robert, Juliette Chausset, Marcel Le Lezec

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Philippe Robert, Juliette Chausset, Marcel Le Lezec. Larval development of Cacopsylla pyri (L.) [Homoptera: Psyllidae] on two resistant Pyrus genotypes. IOBC WPRS Bulletin, 1999, 22 (10), pp.89-91. hal-01600264

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# Larval development of *Cacopsylla pyri* (L.) [Homoptera : Psyllidae] on two resistant *Pyrus* genotypes

Philippe Robert*, Juliette Chausset* & Marcel Le Lézec**

* INH, Institut National d'Horticulture, 2 rue Le Notre, 49045 Angers Cedex 01, France. **

INRA, Station d'amélioration des espèces fruitières et ornementales, 42 rue Georges Morel, 49071 Beaucouzé Cedex, France

**Abstract:** The development of *Cacopsylla pyri* larvae was observed on three *Pyrus* genotypes: cv. 'Katman' and NY 10355, identified as resistant to pear psylla, and cv. 'William's' pear as control. The study was conducted under controlled conditions, on trees grafted one year earlier. One psylla female was placed on each plant and removed after 50 eggs on average had been laid. To record *C. pyri* development, the number of different instars was counted each week on each plant.

On 'William's', larvae completed their development and adults started emerging after one month. Larval mortality was 68 %. On 'Katman' and on NY 10355, young larvae started feeding but all larvae died before completion of their development. In conclusion, under these experimental conditions, complete larval resistance to *C. pyri* was observed on 'Katman' and NY 10355.

**Key words:** *Cacopsylla pyri*, pear psylla, *Pyrus*, pear, host plant resistance.

## Introduction

*Cacopsylla pyri* is the most important insect pest in French pear orchards. Pear psylla produces copious amounts of honeydew that causes leaf necrosis and supports sooty moulds. This insect has developed resistance to different commonly used insecticides. Breeding for resistance to *Cacopsylla pyri* in pear trees offers an interesting alternative to chemical control.

Screening of 71 different genotypes of *Pyrus* has been done in field cages since 1996 at I.N.R.A. Beaucouzé and I.N.H., Angers, France. A dozen genotypes have been identified with a high level of resistance to pear psylla (not published). Two genotypes were selected for this study: 'Katman' and NY 10355. 'Katman' is a cultivar of *Pyrus communis* from Hungary. NY 10355 is a hybrid *Pyrus ussuriensis* x *Pyrus communis* from the United States (USDA). NY 10355 is known to be resistant to another psyllid : *Cacopsylla pyricola*, an important insect pest in American pear orchards.

## Material and methods

The development of *Cacopsylla pyri* larvae was observed on 'Katman' and NY 10355 in 1998. CV. 'William's', known to be sensitive to pear psylla, was the control. This study was conducted in a climatic chamber under controlled conditions: 12 h light / 12 h dark, temperature = 22 / 18°C, relative humidity = 65 / 85%. Trees, that had been grafted, one year earlier on *P. communis*
'Daytor-OHF 87', were grown in pots. Fourteen 'William's' twelve 'Katman' and fourteen
NY10355 plants were used for this study.

One psylla female was placed on each plant within a sleeve of bridal veil. The female was removed after 50 eggs on average per plant had been laid (2 to 7 days). However, this value was exceeded on 'William's' because females tended to lay more eggs on that variety. At the beginning of the observations, an average of 76 eggs per plant were counted on 'William's', 53 eggs on 'Katman' and 46 eggs on NY10355.

To study larval mortality, the number of different instars was counted each week on each plant. However, it was difficult with a hand lens to distinguish between L.1 and L.2 and between L.3 and L.4. Therefore, the different instars were lumped into only four categories : young larvae (L.1 + L.2), intermediate larvae (L.3 + L.4), old larvae (L5) and adults.

## Results and discussion

Psylla development occurred normally on 'William's': the different instars appeared successively (Fig 1). The first adults started emerging after about one month and the latest emerged after about one and half months. Larval mortality was 68% and occurred mainly at the young larval stage (L.1 or L.2).

Larval development did not occur normally on 'Katman' and NY 10355. The results were similar for these two genotypes (Fig.). Eggs hatched, young larvae started feeding and produced small amounts of honeydew. Larval development then stopped : no larvae reached the 3rd instar. Larval mortality was 100% on both 'Katman' and NY 10355.

## Conclusion

Under the controlled environment conditions, complete resistance to *C. pyri* was observed in young plants of 'Katman' and NY 10355. All larvae died before completion of development. Feeding behaviour and movement of young larvae on these two genotypes is currently being studied. This should then indicate whether there is significant resistance occurring at the oviposition phase.

## Résumé

Le développement larvaire du psylle du poirier *Cacopsylla pyri* est étudié sur 2 *Pyrus* : Katman (*P. communis*) et NY10355 (*P. ussuriensis* x *P. communis*). Ceux-ci ont été identifiés comme étant résistants à *C. pyri* lors de cribages antérieurs. William's a été choisi comme témoin en raison de sa sensibilité. L'étude s'est déroulée en chambre climatisée sur 12 à 14 plantes. Les différents stades ont été dénombrés chaque semaine.

Sur William's les larves se développent et les adultes commencent à émerger au bout d'un mois. La mortalité larvaire est de 68%.

Sur Katman et sur NY10355 les jeunes larves commencent à se nourrir et produisent de petites quantités de miellat. Le développement larvaire s'arrête ensuite, la mortalité larvaire atteint 100 %. Dans nos conditions expérimentales, Katman et NY 10355 sont donc totalement résistants à *C. pyri* ; toutes les larves meurent avant d'avoir terminé leur développement.
<figure><img src="image_2.png" /><figcaption>Fig. - Larval development of *Cacopsylla pyri* on William's, Katman et NY 10355: average number of eggs, young larvae (L.1 + L.2), intermediate larvae (L3 + L.4), old larvae (L.5) and adults.</figcaption></figure>

<table><tr><td>eggs</td><td>L1 + L2</td><td>L3 + L4</td><td>L5</td><td>adults</td></tr></table>