The eucalyptus snout beetle, Gonipterus scutellatus (Gyllenhal), introduced to South Africa from Australia, causes extensive damage to eucalyptus plantations in colder regions where biological control is less effective. A cytogenetic study was undertaken to assess the weevil's genetic recombination potential and thereby its ability to adapt to changing environmental conditions. During this study we investigated: (i) the sequence of meiosis; (ii) the weevil's karyotype; and (iii) the number and position of chiasmata on the bivalents. Squashes of male testes revealed a normal, chiasmate meiosis, a sex chromosome complement of Xyp and an autosome complement of three large, and two medium-sized, sub-metacentric pairs and seven small acrocentric pairs. The diploid chromosome number (2n = 26) is marginally higher than the ancestral chromosome number of the Curculionidae (2n = 22). Chiasmata were absent from the proximal regions of the bivalents, occurring mostly in the distal regions and less frequently in the interstitial regions. The mean of 15 chiasmata per cell was marginally higher than the number of bivalents (13); consequently, acrocentric and most sub-metacentric chromosomes displayed a single distal chiasma, while 2–3 sub-metacentrics also displayed a second distal or interstitial chiasma. The relatively low chromosome number and low frequency of chiasmata indicate that genetic recombination is controlled at independent assortment and crossing-over. This may limit the potential of G. scutellatus to proliferate under changing conditions and increase its pest status in the future.
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Vol. 19 • No. 3