No abstract

Two strains of western flower thrips, Frankliniella occidentalis (Pergande), are reputedly found in New Zealand. One strain was recorded in 1934, and it is most common in flowers of Lupinus arboreus outdoors (lupin strain); the other strain was first recorded in New Zealand in 1992 and is found mostly indoors on greenhouse crops (greenhouse strain). Laboratory studies were conducted to compare the life history parameters of these two strains. Thrips from each strain were fed sucrose solution and capsicum or lupin pollen and reared at 25 degrees C, >60% RH, and 16 L:8 D photoperiod. Significant differences in life history parameters were found. Preoviposition time was significantly shorter, and oviposition rate and fecundity were markedly higher (four-fold) for the greenhouse than for the lupin strain. The lupin strain performed significantly better on the capsicum pollen, laying more than twice as many eggs than on the lupin pollen over a 14-d period. The greenhouse strain development time from larvae to adult was marginally faster (0.7-1.1 d less) than the lupin strain because of a shorter prepupal and a marginally shorter pupal development time. Females of the greenhouse strain lived on average 69% longer than females from the lupin strain. Large differences in the intrinsic growth rate (r(m)) were found, with r(m) being 1.4-1.8 times higher for the greenhouse strain than the lupin strain, depending on pollen source. The results are discussed in relation to different ecological requirements and pest status of the two strains.

a b s t r a c tIn a field experiment, we evaluated effects of three different organic white cabbage-cropping systems (O1, O2, O3) on the cabbage root fly, Delia radicum, and its egg predators and pupal parasitoids over 3 years. The three systems all complied with regulations for organic production, but varied in external nutrient input and N-recycling, and were compared to a conventionally farmed control. One organic system (O3) included an intercropped strip of green manure between crop rows. Oviposition by D. radicum was generally not reduced in organic cropping systems. However, higher pupae/egg ratios were observed in the conventional compared to all organic systems, indicating that immature survival from oviposition to pupation was reduced under all the three organic farming practices. In organic system O2 most small coleopteran predators were recorded, but predation on fly eggs was not significantly higher in organic treatments. Pupal parasitization rates ranged from 26.5% to 59.5%, but no significant differences among farming systems were found. Although reduced D. radicum survival could not be attributed solely to natural enemies, the results indicated that organic farming practices in general contribute to the suppression of belowground pests in cabbage production.

The extreme fluctuations of cutworm attacks in Denmark have mainly been related to summer rainfall. In the present investigations the influence on the cutworms was split up and dealt with in the following three ways: Relative air humidity ‐ pilot experiments in the laboratory; rainfall ‐ semifield experiment with sprinkle irrigation of 2 m × 2 m plots; soil moisture ‐ greenhouse experiments using carrots in pots. No indications were found of the effect of the relative humidity or of the effects of falling rain. Soil moisture had a pronounced effect on young cutworms, the mortality of which rose with increasing soil moisture. The experiments showed that young cutworms do not stay permanently on leaves, as described in the literature, but hide in the topmost soil, and this behaviour is disturbed by wet soil. Even though the exact reason for the death of cutworms is still obscure, soil moisture is clearly a major cause of mortality. This information is already used for forecasting of attacks. Improvements may, however, be obtained by building a simple dynamic model when further experimental data are available. Zusammenfassung Bodenfeuchtigkeit als Mortalitätsfaktor bei der Wintersaateule, Agrotis segetum Schiff. (Lep., Noctuidae) Das Auftreten von Erdraupen der Wintersaateule in Dänemark fluktuiert sehr stark. Viele Autoren haben einen Zusammenhang zwischen der Fluktuation und den Niederschlagsmengen gefunden. In der vorliegenden Untersuchung wurde die Bedeutung des Niederschlages in jene von relativer Luftfeuchtigkeit (Pilotversuche), fallendem Regen (Semi‐Feldversuche) und Bodenfeuchtigkeit (Gewächshausversuche mit Möhren in Blumentöpfen) gegliedert. Kein Einfluß konnte seitens der Luftfeuchtigkeit oder der Regenmenge festgestellt werden. Dagegen wurde unter den Jungraupen eine sehr hohe Mortalität gefunden, die von der feuchten Erde verursacht war. Während der Experimente wurde die Beobachtung gemacht, daß die Jungraupen sich nicht ‐ wie früher behauptet ‐ permanent an den Blättern aufhalten. Dieses Verhalten war bei nasser Erde gestört. Obwohl der genaue Grund, warum die Jungraupen sterben, unbekannt ist, kann geschlossen werden, daß steigende Bodenfeuchtigkeit steigende Jungraupenmortalität zur Folge hat. Diese Erkenntnis ist für die Prognose von Erdraupenbefall von Bedeutung. In Dänemark wird sie schon verwendet, um die Schadensgefahr zu veranschlagen, aber es wäre wünschenswert, noch mehr experimentelle Daten zu besitzen, um ein einfaches dynamisches Modell als Grundlage für eine Verbesserung des Prognoseverfahrens entwickeln zu können.

Three species of Entomophthorales were found on adult carrot flies (Psila rosae F.) during two successive seasons: Entomophthora rnuscae (C.) Fres., Conidiobolus apiculatus (Thax.) Remaud. & Keller and Erynia sp. E. muscae was by far the most common species and caused epizootics in one carrot fly population up to 3 times per year. Flies caught in the hedge showed a higher infection level than flies caught in the field close to the hedge. Flies caught 200 m away from the hedge showed the lowest infection level. Apparently the hedge was the site of infection, since carrot flies, killed by E. muscae, were found there attached to the underside of the leaves. Flies caught on yellow sticky traps developed only to a limited extend symptoms and gave little information about the fungus infection levels.