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Oviposition sites of Phlyctinus callosus (Schoenherr) in an apple and a nectarine orchard in the South Western Cape, South Africa, were investigated. No eggs were found on the fruit trees, only in different fractions of the orchard floor, viz. in orchard weeds, leaf litter and soil. Significantly more oviposition took place in plant material on the orchard floor than in the top 20 mm of the soil. Microscopic dissection of samples of such plant material revealed that females prefer to oviposit in confined or hollow spaces in moist, live or decaying plant tissue on the soil surface or in weeds comprising the cover-crop. P. callosus females favoured certain weeds above others for oviposition. The dispersion pattern of eggs in the cover-crop was contagious. The implications of the observed oviposition behaviour in terms of control strategy, and for exploitation in a monitoring system for this species, are discussed.
The seasonal fruit‐feeding behaviour of adults of Phlyctinus callosus in Granny Smith apple orchards, and the extent of the resultant crop loss was monitored on two farms during a number of successive seasons. Fruit feeding started at fruit set and reached maximum levels within 6 weeks. Thereafter, it abruptly decreased, even though there were still some 10 weeks to harvest. Evidence indicates that the sudden decrease in fruit‐feeding is due to a reduction in the functional value of adult mandibles caused by feeding. Renewed periods of fruit feeding on a smaller scale sometimes occurred in mid‐season and shortly before harvest. These periods were closely related to periods of increased adult emergence. The dispersion pattern in the trees of fruit damaged by P. callosus was contagious, indicating aggregation behaviour during feeding by this species. The crop loss in apple orchards due to uncontrolled populations of P. callosus was very variable. Fruit damage between trees varied from less than 1% to 66%, and mean crop loss between seasons from 5% to 29%. Between 70% and 99% of fruit damage was caused during the first 3 months after fruit set. The implications of fruit feeding behaviour for the economic management of P. callosus are briefly discussed.
Zusammenfassung
Untersuchungen zum Fraßverhalten von Phlyctinus callosus (Schönberr) (Col., Curculionidae) in Apfelbaumkulturen
Es wurde das Fraßverhalten adulter Phlyctinus callosus an Früchten während der gesamten Vegetationsperiode in einer Granny‐Smith‐Apfelbaumkultur untersucht. Daneben wurden auf zwei Farmen in mehreren aufeinanderfolgenden Jahren die Ernteverluste ermittelt. Der Fruchtfraß begann zum Zeitpunkt des Fruchtansatzes und erreichte innerhalb von sechs Wochen seinen Höhepunkt, ließ dann plötzlich nach, obwohl es noch ca. 10 Wochen bis zur Ernte dauerte. Es gibt Hinweise dafür, daß die plötzliche Abnahme des Fruchtfraßes durch Abnutzungserscheinungen der Mandibeln ausgelöst wird. Eine erneute Fruchtfraßperiode trat teilweise mitten in der Saison oder kurz vor der Ernte auf. Diese Zeiträume sind eng korreliert mit dem Anstieg des Adultenschlupf. Das Verteilungsmuster der beschädigten Früchte innerhalb eines Baumes deutet auf ein Aggregationsverhalten der Käfer während der Fraßzeit hin. Der Ernteverlust in den Apfelkulturen durch nicht‐bekämpfte P. callosus‐Populationen schwankte sehr stark. Die Fruchtschäden zwischen den Bäumen variierten von weniger als 1% bis 66% und der mittlere Ernteverlust lag zwischen 5 und 29%. Etwa 70 bis 99% des Fruchtschadens wurde in den ersten drei Monaten nach dem Fruchtansatz verursacht. Der Einfluß des Fraßverhaltens von P. callosus wird in Bezug auf die wirtschaftliche Behandlung kurz diskutiert.
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