Helmut Saucke

Response of alate aphids to green targets on coloured backgrounds

To study the effect of background colour on aphid landing on green targets (water pan traps), two field experiments were set up in Hessen, Germany, in 2003. Traps were put onto coloured plastic sheets (13 colours, straw mulch, transparent foil, and uncovered soil, Experiment 1). In Experiment 2, green water pans were again put on coloured plastic sheets (red, white, green, and yellow), and the sheets were either sprayed with insect glue or not. Backgrounds and traps were spectrally characterised with a field radiometer (320–950 nm). Aphid catches were highest in the traps on the uncovered background, and lowest in the traps on white or silver backgrounds. For Brevicoryne brassicae, Myzus persicae (Homoptera: Aphididae, Macrosiphini) and five further aphid species, there was a significant negative correlation between UV‐reflectance (320–400 nm) and log(N + 1)‐transformed number of individuals. However, the effect of straw mulch (reduced aphid catches with straw compared to the uncovered background), could not be attributed to differences in UV‐reflectance, as UV was almost identical in soil and straw. High numbers of alate aphids were caught in traps with dark backgrounds (e.g. black, dark green), a result which was attributed to the high contrast between the background and target. The substantially higher aphid numbers from targets with bare soil than from targets with spectrally similar black backgrounds were thought to be caused by the structure of the background surface: for alate aphids, landing close to the target on smooth surfaces may induce probing, and the lack of appropriate substrate will result in take‐off, whereas soil will not induce probing, and aphids will continue to move towards the green targets.

Biological and Integrated Control of Plutella xylostella (Lep., Yponomeutidae) and Crocidolomia pavonana (Lep., Pyralidae) in Brassica Crops in Papua New Guinea

The major constraint to the production of good quality cabbage in Papua New Guinea (PNG) is posed by a complex of insect pests which includes the Diamondback Moth Plutella xylostella (L.) as the most prominent species. In order to evaluate the prospects of a classical control approach economically important major pests and their natural enemies were surveyed in three cabbage growing areas with distinct climatic regimes at low-, mid- and high-elevation. In the PNG highlands (Goroka and Tambul area, Western Highlands Province) the release and successful establishment of the P. xylostella -specific parasitoid Diadegma semiclausum (Hellen) reduced crop losses remarkably since 1995. Favourable circumstances, such as continuous brassica cultivation and low status of associated lepidopteran pests, particularly at Tambul (2400 m above sea level) with an almost temperate climate, were supportive for this approach. In the arid PNG lowlands (Laloki area, Central Province) the introduced P.xylostella -parasitoid Cotesia plutellae (Kurdjumov) exerted 80% parasitism in an experimental site, although a lasting establishment was not achieved in that location. Among several indigenous P. xylostella parasitoids Brachymeria phya (Walker) was a ubiquitous species but did not reduce the pest status of its host. Natural enemies of associated lepidoptera such as Crocidolomia pavonana (Zeller), Spodoptera litura (F.), Helicoverpa armigera (Hübner) and Hellula undalis (F.) were economically insignificant. Thus, insecticidal control, preferably selective, was still a requirement. In comparison to Bacillus thuringiensis -products (Delfin ® and Thuricide ® ) and the synthetic insect growth regulator Chlorfluazuron (Atabron ® ), best results were achieved in field trials with the commercial neem formulation NeemAzal ® ( Azadirachta indica A. Juss.) and an aqueous neem seed kernel extract from seeds of PNG grown trees. Besides its high efficacy against lepidopterous pests, neem also controlled the false mustard aphid Lipaphis erysimi (Kalt.), being of economic importance in the arid PNG lowlands. The prospects of integrating C. plutellae into a reduced insecticide spraying program as well as alternative cultural control measures are discussed.

Key factors affecting the spring emergence of pea moth (Cydia nigricana)

The hypothesis that spring emergence of the pea moth Cydia nigricana is regulated by environmental factors, particularly photoperiod and temperature, was examined in this study. A long-term field study was conducted in two distinct pea-growing areas in Hesse and Saxony, Germany. Strong correlations between the flight phenology of pea moth in spring and air temperature, soil temperature, solar radiation and day length were demonstrated for three consecutive years. In laboratory experiments, we elucidated the interaction of different photoperiod-temperature regimes, verifying cumulative day-degree data in relation to pea moth emergence rates in the field. C. nigricana temperature sensitivity is apparently initiated by long day conditions with a critical day length of about 14 h L:D. The overall results contribute to the theory that photoperiod and temperature interact as regulatory cues for spring emergence of C. nigricana. The findings are discussed in terms of the development of predictive models and decision support systems for pea moth control.

Risk assessment of pea moth Cydia nigricana infestation in organic green peas based on spatio-temporal distribution and phenology of the host plant

1 A method for area‐wide risk assessment of pea moth infestation in commercial pea‐growing areas based on spatial and temporal analyses of pea moth abundance and the phenological distribution of pea fields was investigated. 2 In a commercial pea‐growing region in Saxony, Germany, all pea fields were identified, mapped and characterized, recording the pea plant phenology, pea moth flight and larval infestation of each field in the years 2006–2008. 3 The relationship between pea moth flight and pea plant phenology was studied in detail in small‐scale field experiments in Hesse, Germany, using different pea cultivars and sowing dates. 4 In the study area, the abundance of Cydia nigricana Fabricius (Lepidoptera: Tortricidae) in organic green peas increased linearly with the pea‐cropping area of the previous year in the surroundings of the current fields according to the continuous abundance index. 5 Considering solely the early flowering period (= early pea sowing dates) of the organic green peas, we calculated that a minimum distance of the current pea field to the nearest pea field of the previous year of 500 m was necessary to significantly reduce pea moth flight and larval infestation. 6 In small‐scale field experiments, a correlation between pea moth flight and larval investation, as well as the importance of the pea flower for the pea moth occurrence, was demonstrated. 7 The spatio‐temporal findings are discussed in relation to the development of a coincidence avoidance strategy in pea‐growing areas.

Mating disruption of pea moth (Cydia nigricana) in organic peas (Pisum sativum)

We appraised mating disruption (MD) to control pea moth, Cydia nigricana (Fabricius) (Lepidoptera: Tortricidae), by assessing male attraction to monitor traps, larval pod infestation, and larval age structure in pheromone‐treated and untreated grain pea fields [Pisum sativum L. (Fabaceae)], over a 5‐year period. Cellulose pheromone dispensers were manually attached to the top shoots of pea plants and released 540 mg ha−1 day−1 synthetic pheromone E8,E10‐dodecadien‐1‐yl acetate in a first test series (2000–2001) and ca. 4 200 mg pheromone ha−1 day−1 in a second series (2004–2006). The dispensers had a half‐life of about 30 days. Although male attraction to pheromone monitoring traps was largely suppressed at the edges and within MD fields in both test series, MD treatments did not reduce pod infestation in the open field in 2000 and 2001. In the 2004–2006 series, larval damage reduction was achieved in the majority of the trials but overall MD efficacy in the open field was only 61% and not significant. In contrast, in field cages placed within the experimental sites and supplied with unmated pea moths, MD control was consistently high and significant. There were no obvious differences in the larval age distribution in all MD and control treatments, suggesting that infestations started and developed further similarly. As a univoltine species, C. nigricana larvae stay in the soil of pea fields for hibernation and pupate. The following year, emerging adults disperse and fly to the closest pea crop. Combined emergence site and pea crop treatments were conducted over 2 years to include this early migration phase of C. nigricana adults. However, the emergence site treatments did not enhance MD‐control efficacy. We conclude that mating activity was only prevented in cage tests, whereas substantial mating occurred during the transit phase outside the pheromone‐treated fields either within non‐crop vegetation and/or at the edges of pheromone‐treated pea fields orientated upwind. Thus, resulting gravid female entry can be regarded as the major constraint to reliable MD control.