| It is very difficult to identifiy the scolytid because of its small body and morphological complexity. Four species of ambrosia beetles attacking Largeleaf hydrangea were found in2009, one of which was Xylosandrus gremanus, and the others could not be determined yet. It is very late to begin to study the scolytid in China, especially ambrosia beetles. At present, more in-deepth and systematic study on ambrosia beetles were reported on Xylosandrus gremanus attacking grapevine and its ambrosia fungi by Yang Qunfang(2009), Zhang Guangquan(2008), Han Julan(2009) and Wang Hui(2010),while the life history and habits of few ambrosia beetles has been obversed. The morphological characteristics and anatomy of the alimentary cannal of3species of ambrosia beetles attacking Largeleaf hydrangea were studied, and the premary ambrosia fungi of4species of beetles were isolated and identified in this paper. The results are as follows.1.Morphological characteristics of3species of ambrosia beetles attacking Largeleaf hydrangea were studied by stereo and scanning electron microscopy.The results showed that3species of ambrosia beetles were X. brevis, X. discolor and X. compactus. The key characteristicses to identify X. brevis adult female are:(1) the body is2.30to2.86mm long.(2) pronotum and elytron were all dark tawny-colored.(3) From pleural view,the anterior2/3of elytron was straight, the posterior1/3sharply descended to be a section.(4) there was semi-appressed hairs in the striae and interstriae on section, and a list of spilliness in the interstriae.The key characteristicses to identify X. discolor adult female are:(1) the body is1.86to2.10mm long.(2) Pronotum was tawny, but elytron was dark brown on the hind wing.(3) From pleural view,the anterior2/3of elytron was straight, the posterior1/3sharply descended to be a section.(4) There was semi-appressed hairs in the striae and interstriae on section, and a list of erect, long and narrow hairs in the interstriae. The key characteristicses to identify X. compactus adult female are:(1) the is2.0to2.3mm long.(2)The anterior half of elytron is shining.(3)With limited exceptions granulate-punctate on interstriae of elytral declivity.2.The anatomy of the alimentary cannal of3species of ambrosia beetles were studied.The results showed that the alimentary cannal of4Xylosandrus species were all composed of foregut, midgut and hindgut.Proventriculus all composed of8proventricular plates were lantern-shaped. They all had six Malpighian tubules, which were arranged in one group of four and another of two. The six Malpighian tubules and the hindgut wall constituted the cryptonephridial system. Their gastric caecas were all located at the posterior region of midgut. However, X.brevis only had a pair of capitate-shaped gastric caeca while X.discolor only a pair of clavate-shaped gastric caeca. X.compactus and X.gremanus all had a pair of sac-shaped gastric caeca posterior, however, the former had a pair of clavate-shaped gastric caeca,while the latter a pair of tuble-shaped gastric caeca anterior. These indicated that2coupples of beetle species adult could be identified by gastric caeca. Additonally, regardless of the species, the foregut constituted about33%,the midgut21, and the hindgut45%of the total alimantary canal length.3.The premary ambrosia fungi of4species of beetles were isolated from mycagium. According to the morphological and cultural characteristics, the premary ambrosia fungi of X. brevis and X. gremanus were identified as Ambrosiella hartigii, that of X. compactus was Ambrosiella xylebori, while that of X discolor was not identified yet.4. The sequence analysis of28S and18S ribosome RNA gene was also used to identify the premary ambrosia fungi of X. brevis, X. gremanus and X. compactus.The sequence homologies of28S and18S ribosome RNA were98.3%and99.3%when the premary ambrosia fungi of X. brevis identified by morphology was compared with the sequences of A. hartigii retrieved from GenBank. The sequence homologies of28S and18S ribosome RNA were99.1%and99.7%when the premary ambrosia fungi of X.germanus identified by morphology was compared with the sequences of A. hartigii retrieved from GenBank. The sequence homologies of28S and18S ribosome RNA were97.9%and97.3%when the premary ambrosia fungi of X. compactus identified by morphology was compared with the sequences of A. xylebori retrieved from GenBank. These results indieated that the premary ambrosia fungi of3species of beetles were all Ambrosiella.The, sequence homologies and evolutionary relationship of rDNA-ITS was analysis the premary ambrosia fungi of X. brevis, X. gremanus, X. discolor and X. compactus. the premary ambrosia fungi of X. brevis and X. gremanus was the same species. |
