OVARIAN DEVELOPMENT IN OVERWINTERING PEAR PSYLLA, CACOPSYLLA PYRICOLA (HOMOPTERA: PSYLLIDAE): SEASONALITY AND EFFECTS OF PHOTOPERIOD

Abstract

Effects of photoperiod, time of year, temperature, and an insect growth regulator (fenoxycarb) on ovarian development rate in overwintering pear psylla, Cacopsylla pyricola (Foerster), were determined. Winterform pear psylla were collected from the field at intervals between October and February, and reared at 20 °C and one of three treatments: short-day photoperiod, long-day photoperiod, or short-day photoperiod + fenoxycarb. Insects were then dissected at intervals to score ovarian development. Baseline scores (i.e., ovarian development in the field on date of collection) increased very slowly between October and February. By mid-February, only about 20% of insects in the field were categorized as having postdiapause status based upon ovarian development. In the laboratory, time required for insects to reach postdiapause status decreased between the October and February collection dates. Number of days necessary for 50% of the long-day insects to reach postdiapause status was approximately 2 weeks in October, 6 days in December, and < 2 days in February. Short-day insects also required fewer than 2 days in February, but required > 2 weeks in the October and December samples. Our results suggested that insects collected in January and February had completed diapause but that ovarian development was subsequently prevented in the field by low temperatures. Fenoxycarb caused rapid ovarian development even in October-collected insects; rate of development was only slightly more rapid in the February-treated psylla.

Phenological model of pear psylla Cacopsylla pyri

“…Our observations on C. pyri concur with those made by Horton et al. (1998) and Krysan and Higbee (1990) on C. pyricola , namely that reproductive diapause terminates during mid to late winter and that ovarian development rates exhibit large variation.…”

Attraction of male pear psylla, Cacopsylla pyricola, to female‐infested pear shoots

“…Winterform psylla were collected from a commercial orchard in mid to late February 2003 and 2004. Psylla collected at this time of year have completed diapause, but require warming temperatures before mating and egg‐laying commence (Krysan & Higbee, 1990; Horton et al., 1998). The insects were stored at 3 °C in 2 l plastic containers partially filled with slightly moistened tissue paper, until they could be assayed.…”

“…Management recommendations for pear psylla emphasize control of the overwintered generation or immature off-spring of the overwintered generation (Westigard & Zwick, 1972), as this prevents potentially severe problems later in the growing season. Thus, it is important to understand biology of the post-diapause winterform, and a great deal of research has been done addressing aspects of postdiapause development, dispersal, host plant colonization, and monitoring for this morphotype (Krysan & Higbee, 1990;Horton et al, 1992Horton et al, , 1998Horton, 1999). Post-diapause winterforms are active in pear orchards well before foliage shows in the pear tree, and at this time exhibit a statistically clumped distribution among trees (Burts & Brunner, 1981).…”

Controversial aspects of diapause development

“…While the term photoperiodic (re)activation is adequate for the described mechanism and has since been generally used, the term cold reactivation has gradually been aban doned in papers published in English, evidently due to the Leinaas & Bleken, 1983Hunter & Gregg, 1984Groeters, 1994Fisher et al 1996Fisher, 1997Du Merle, 1999Pires et al, 2000Regniere, 1990Menu, 1993Yamanaka & Fujiyama, 1994Lopez et al, 1995Ishihara & Shimada, 1996Miles et al, 1998Tadini-Vitagliano et al, 1982Reisen et al, 1995Mochizuki & Takafuji, 1996Horton et al, 1998Watanabe & Tanaka, 1998 *dry/cool season dormancy in a tropical insect (Di: IV-VII, post-Di quiescence:VII-X) repeated findings that in the course of overwintering dia pause the endogenous inhibition s p o n t a n e o u s l y disappears as early as in mid-winter (Table 1). This dis crepancy led the Russian authors to use a more adequate term -cold sensibilisation (Zaslavsky, 1988).…”