Geographic and seasonal variability of resistance to insecticides in Cacopsylla pyri L. (Hom., Psyllidae)

Abstract

Pear psylla (Cacopsylla pyri L.) resistance to insecticides was studied in adults using the topical application method. In the Avignon population, the winter forms tested (diapausing generation) showed a greater tolerance to insecticide than the summer forms. High resistance rates, ranging from 25‐ to 180‐fold, were observed for three organo‐phosphorous insecticides. Resistance rates were seven times lower for pyrethrinoids and amitraz and practically nil for carbamates. Inter‐population resistance rates, for an identical period, were different for the three organo‐phosphorous insecticides and for deltamethrin in two localities. However, it was difficult to make comparisons in time due to seasonal variations. Rates of synergism by S,S,S‐tributyl phosphorotrithioate (DEF) and piperonyl butoxide (PBO) were low when applied 4 h before the insecticide (0.3‐ to 3.3‐fold), except for deltamethrin with PBO (>60‐fold). The presence of mixed‐function oxidases in winter forms is discussed with regard to bibliographical data concerning another psylla species from North America (Psylla pyricola Foerster).

Resistance of pear psylla (Cacopsylla pyri L.; Hom., Psyllidae) to deltamethrin and synergism with piperonyl butoxide

“…The following results were obtained here on the synergism between deltamethrin and PBO: (i) the rate of synergism between deltamethrin and PBO was more than 10‐fold in all the adult populations (except those from Monêtier: RS = 6.3), in both the summer and the winter forms, (ii) the synergistic effects observed at the larval stage were similar to those observed in the adults, (iii) there was no correlation between the sampling dates and the rates of synergism, (iv) there was no correlation between RR and RS, and (v) deltamethrin was the only one of the three pyrethroïds which was clearly synergized by PBO. The authors of a previous study (B uès et al, 1999) observed no synergism between three organophosphorous (azinphosmethyl, phosmet and monocrotophos) and PBO. When PBO was applied before deltamethrin, the slopes of the regressions were generally smaller than those obtained without PBO.…”

“…However, this increase was not so sharp during the winter of 1998–1999. These results makes it impossible to state whether the winter form is always more resistant to deltamethrin than the summer form, as has been observed with organophosphates (B uès et al, 1999). Although this orchard did not undergo any specific treatments against psylla or the codling moth during the observation period, there were strong fluctuations in the RR during this period.…”

“…On a selected strain with monocrotophos, modified acetylcholinesterase (AChe) was observed and the activity of mixed function oxidase increased. Furthermore, this species is resistant to other organophosphates (azinphosmethyl and phosmet) ( Buès et al, 1999). Two pyrethroids, deltamethrin and cypermethrin, have been widely used against pear psylla, and their use is extended to the control of other pear pests, especially the codling moth ( Cydia pomonella L.) and aphids.…”

“…The ovarian development resumes from mid‐January ( Rieux and Faivre d’ Arcier , 1990). Like C. pyricola in North America, the summer form of C. pyri is more susceptible to insecticides than the winter form ( Van de Baan and Croft , 1991; B uès et al, 1999). Bioassays carried out on wintering adults with deltamethrin in 1996 yielded resistance rates of 18‐and 43‐fold in two populations located in the southern part of the Rhône Valley ( Buès et al, 1999).…”

“…Like C. pyricola in North America, the summer form of C. pyri is more susceptible to insecticides than the winter form ( Van de Baan and Croft , 1991; B uès et al, 1999). Bioassays carried out on wintering adults with deltamethrin in 1996 yielded resistance rates of 18‐and 43‐fold in two populations located in the southern part of the Rhône Valley ( Buès et al, 1999). The tests carried out on the synergism between deltamethrin and PBO applied to one of the two populations showed the occurrence of a high rate of synergism (>60 times) and suggested the presence of mixed function oxidase.…”