Selection for monocrotophos resistance in pear psylla, Cacopsylla pyri (L.) (Hom., Psyllidae)

Abstract

Pear psylla, Cacopsylla pyri (L.), adults collected from commercial pear orchards around Toulouse (France) were selected in the laboratory for resistance to monocrotophos. Resistance was obtained only when the insecticide selection pressure was continuous, but when some generations were not selected, resistance did not develop or even reverted. Resistance appeared to be stable after 30 generations of selection and stabilized at a level of 140-fold. The monocrotophos-selected strain was highly cross-resistant to the organophosphate phosmet (1 55-fold) and cross-resistant to the formamidine amitraz (1 4-fold).

Genetic analysis of resistance to azinphosmethyl in the pear psylla Cacopsylla pyri

“…Laboratory selection pressure, did not markedly increase resistance over 17 or 23 generations implying a high level of homozygosity for resistance in the original field collections. This result differed from that observed by Berrada et al (1995) on C. pyri who, by selection with monocrotophos, increased the resistance rate from 25-fold to 130-fold in 18 generations. These authors also demonstrated that the resistance levels attained in the laboratory can only be maintained by exerting a constant selection pressure, a procedure that has not been tested in the present study.…”

“…Tests with pyrethroids, amitraz, and carbamates did not reveal any particular tolerance of strains R1 and R2 to these insecticides. Berrada et al (1995) also noted strong cross-resistance between monocrotophos and phosmet (155-fold). Crossing of strains R1 and R2 to the susceptible strain indicated that resistance was semi-dominant.…”

“…In North America, research on Cacopsylla pyricola Foerster (Homoptera: Psyllidae) demonstrated their resistance to different insecticide classes (Follet et al, 1985;Burts et al, 1989;Pree et al, 1990). In France, a selection experiment with monocrotophos, conducted over 40 generations (Berrada et al, 1995), resulted in 140-fold resistance compared to the untreated strain, but no crossing between strains was undertaken. The number of genes involved and the degree of dominance of resistance alleles can influence the development, expression, and stability of resistance (Roush & Daly, 1990).…”

The Past and Present of Pear Protection Against the Pear Psylla, Cacopsylla pyri L.

“…Among the C. pyri resistance events in Europe the best known involve organophosphorates, pyrethroids and chitin inhibitors: in all documented cases a sharp decrease in pesticide activity was observed even after a few years of use. The active ingredient monocrotofos represents the best known case (Berrada et al, 1995 Table 4. Results of three field trials with spirodiclofen on three pear tree varieties Boselli & Cristiani, 2008).…”

Survey of Susceptibility to Abamectin of Pear Psylla (Hemiptera: Psyllidae) in Northern Italy

“…Monocrotofos (an organophosphorous compound) is the best known example: the selection carried out by this insecticide on C. pyri populations led to an increase of pest resistance rate from 25-to 130-fold in only 18 generations (Berrada et al 1995). The same event occurred for Azinphos methyl (Buè s et al 2000).…”