75: 923-926. Photosensitization of livestock in Nova Scotia has often been attributed to St. John's wort (Hypericum perforatum L.), even though the weed generally occurs at low densities. This study's objective was to determine whether levels of hypericin, the photodynamic toxin causing photosensitization, were unusually high in Nova Scotia biotypes and whether levels increased in late spring, when photosensitization most commonly occurs. The mean hypericin content in vegetative growth of I I Nova Scotia 1L perforatum biotypes was 195 pg g-l dry wt, whereas levels in biotypes from British Columbia and Australia were at least two-and ttneefold higher, respectiveiy. HvetJ in field-collected plants were lowest in May (60 lrg g-l dry wt) and peaked in midsummer (160-280 pg g-l dry wt). In a controlled-environment study, hypericin levels increased linearly with increasing temperatures. Furthermore, hypericin levels were not affected by infection by Colletotrichum gloeosporioi'des.Thtts, the hypericin content of Nova Scotia biotypes is too low to be the cause of photosensitization in livestock.

No abstract

An organophosphate pyrethroid-resistant strain of Typhlodromus pyri Scheuten imported from New Zealand was reared on potted apple trees in an outdoor insectary. From 1988 to 1995, the population was selected one to three times per year with a dilute solution (1.7 ppm) of the pyrethroid cypermethrin. Petri dish bioassays with cypermethrin in 1995 indicated that the insectary-reared T. pyri had an LC50 of 81 ppm versus 0.006 ppm for native T. pyri taken from a research orchard. The bioassays suggested that recommended orchard rates of cypermethrin would cause heavy mortality in native populations of T. pyri but only moderate losses in the imported New Zealand strain. Bioassays in 1996 with the organophosphate insecticide dimethoate indicated both New Zealand and native T. pyri were susceptible and that recommended orchard rates of dimethoate likely would cause high mortality of T. pyri in apple orchards. These findings from bioassays were supported by data from orchard trials. In June and July 1993, insectary-reared New Zealand T. pyri were placed on five apple trees in each of eight 38-tree plots in the research orchard. In late August 1994, New Zealand T. pyri from orchard trees that had been sprayed twice by airblast sprayer with the full recommended rate of 50 g (AI)/ha (83 ppm) cypermethrin were placed on the other 33 trees in each of six plots. In the summers of 1994-1996, plots were treated with one of the following insecticide regimes: (1) conventional integrated pest management (IPM) (registered neurotoxic insecticides considered harmless or slightly toxic to T. pyri); (2) advanced IPM (use of newer, more selective insecticides); (3) pyrethroid (at least one full-rate application of cypermethrin); (4) dimethoate; and (5) dimethoate plus pyrethroid. Densities of European red mite, Panonychus ulmi (Koch), were highest in all plots treated with dimethoate and in pyrethroid plots not yet inoculated with New Zealand T. pyri. Densities of apple rust mite, Aculus schlechtendali (Nalepa), and of the stigmaeid predator Zetzellia mali (Ewing) were highest in plots treated with dimethoate and were nearly absent in the IPM plots. Densities of T. pyri were high enough for effective biocontrol in the IPM plots and in the pyrethroid plots 1-2 yr after release of the New Zealand strain, provided pyrethroid was applied just before the resistant strain was released in the orchard. A recurring theme of this study was the generally negative association between densities of phytophagous mites and those of T. pyri, suggesting the ability of this predator to suppress their prey. In contrast, the positive association between phytophagous mites and Z. mali suggests the inability of this predator to regulate their prey at least under the conditions of this study.

This study assessed the effects of Surround (kaolin) on several behavioral parameters of female blueberry maggot, Rhagoletis mendax Curran (Diptera: Tephritidae). First fruit visited, walking, cleaning, and oviposition behavior were quantified in two-choice and no-choice assays where females encountered Surround-treated and untreated fruit of highbush blueberries (Vaccinium spp.). In two-choice assays, females had a propensity (68%) to first visit untreated blueberries. In two-choice and no-choice tests, number of walking bouts and duration of walking bouts were significantly shorter on the Surround-treated than on untreated fruit. Few oviposition attempts on fruit were observed, irrespective of treatments and assays. Chromameter measurements showed significant modification of the blueberry skin color parameters lightness, hue, and saturation between untreated fruit compared with fruit dipped once or twice in a suspension of Surround. Oviposition trials with field-treated fruit showed that blueberries treated with Surround had fewer oviposition scars than the control, and this was more pronounced with weekly applications of Surround. Uneven coating of the fruit by Surround in field applications may have resulted in higher acceptance rates by flies than in blueberries individually dipped and used in laboratory trials.

No abstract