S. Mahunka szerk.: Folia Entomologica Hungarica 52. (Budapest, 1992)

Xyleborus affinis attacks mainly unhealthy, damaged or felled trees but occasionally infests healthy stands as well (Schedl 1963, Bright 1968) It prefers trunks and larger branches to roots close to the ground surface. Slender and stout parts are equally attacked but higher individual number is found in trees 8 to 30 cm in diameter (Schedl 1963). As vector of pathogenic fungi, it may cause severe secondary damage (Carter 1962, Beaver 1976) The gallery system excavated by the females is 3-dimensional, different in the various hosts and the extension depends on the diameter of the attacked part. The tunnels are usually formed horizontally in the xylem perpendicularly to the fibres ramifying irregularly. In slenderer stems, vertical tunnels may issue from the horizontal gallery. In some plants (Dialium corbisieri, Entadopsis abyssinica, Gossweilerodendron balsamiferum, Pterocarpus tinctorius) the majority of the tunnels is developed in the phloem between the bark and the sapwood (Schedl 1963). Xyleborus affinis is an ambrosia beetle, i. e. is associated with symbiotic ambrosial fungi. The term 'ambrosial fungi' is a collective term of various fungus species serving as food of wood-boring insects (Müller 1980). Adults have a paired mycetangium at the base of the mandibles. The newly emerged teneral females take up fungal fragments and the mycetangium is full of fungus 12 hours after the beetle attains its final colouration (Schneider 1987) The symbiotic fungi are propagated in the gallery system and soon the wall of the tunnels is covered by fungal layer. Eggs are laid irregularly in the tunnels and the larvae feed upon the fungi. There are 3 larval stages (Roeper and al. 1980). The rate of males and females is 1:42 in vivo (Schedl 1963) while 1:9 in vitro (Roeper and al. 1980) Copulation takes place in the gallery system as the males do not leave their breeding place (Bright 1968). According to Schedl (1963), owing to the low percentage of the males the possibility of parthenogenesis cannot be excluded. About 24-27 °C is required for hatching of the eggs and emergence of the mature females (Schedl 1963). In tropical conditions, one generation develops in 5 to 6 weeks (Schedl 1963). The gallery system is inhabited and extended by several generations until the moisture content of the wood becomes unfavourable for growth of the symbiotic fungi. Pest control Owing to the concealed way of life of Xyleborus affinis, the control of the infestation is insufficiently resolved as yet. According to Hamlen and Woodruff (1975), the populations of the pest can be suppressed by chemical or heat treatment. For chemical treatment, the unsprouted canes are immersed in 0.5-2% solutions of Lindane 25 WP or Chlordane 72 EC for 15 min. During the heat treatment the canes are held for 30 min in water at 46 °C then cooled in 25 °C water for 10 min. These treatments effectively reduce the number of adults, larvae and pupae and cause no phytotoxicity. Acknowledgements - Thanks are due to Ing. Carolus Holzschuh (Forstliche Bundcsversuchsanstalt, Wien) for identifying of the beetle specimens and for some literature. The habitus drawings were prepared by Mr. János Pál.