| Xylosandrus germanus(Blandford)(Coleoptera:Scolytidae) is a new destructive pest attacking grapevine in Chendu.The adult females excavate galleries in wood.As a result, the vigor of grapevine descends,even the trees die off.It is very difficult to study and control the beetle because of its small body and secluded life.Aiming to provide a basis for the pest management and further reveal symbiosis between the beetle and fungi,the biology,ecology and ambrosia fungi of the beetle were studied,and the results are as follows.1 Identification of X.germanusMorphological characteristics of X.germanus were studied by stereo and scanning electron microscopy.The key characteristicses to identify the beetle are:1) the adult female is 2.02 to 2.26 mm long,and the adult male is 1.00 to 1.30 mm long;2) the anterior half of elytron is shining,while there is long hair on the hind half;3) there is long hair only in the interstriae of the posterior half of elytron,whereas the adult males' elytrons can not be divided into striae and interstriae;4) the mycangium is pro-mesonotal.These characteristicses showed that the beetle attacking grapevine is Xylosandrus germanus (Blandford).Furthermore,two morphological characteristics were found by scanning electron microscopy,they are:1) hair in the sculpture of the costal margin of the adult's prothorax is divided into two branches,the female's is serrate while the male's is pectinate; 2) there is very short hair in the sculptures which have not long hair in the elytrons.The anatomy of the alimentary cannal of X.germanus was described for the first time home and abroad.The adult's proventriculus plate is composed of anterior plate and posterior plate,the former is shorter and simpler,and the later is longer,composed of declivity,masticatory brush and stopping bristles.The plate structure is likely related to the beetle's mycetophagous habit.The adults have a pair of tuble-shaped and a pair of sac-shaped gastric caeca,being located in the posterior portion of midgut.That there are a pair of tuble-shaped and a pair of sac-shaped gastric caeca in the alimentary cannal is one of the identification characteristics of the adult.2 The biology and ecology of X.germanusThe biology of X.germanus were clarified by field observation and indoor breeding. It had three to four generations per year with partial generation,and overwintered as the adult females clustering in the galleries of bole base of grapvines.There were two peaks of flight activity in a year,the bigger one was the overwintered females' flight activity.The gallery system was composed of one entrance tunnel,one brood chamber and three to five branch tunnels.When the adult females were fed in semi-artificial diets and grapevine logs, the sex ratio was 10.7 female:lmale,and 10.3 female:lmale,respectively.When they fed on Acremonium kiliense at 25℃,the larvae had three instars.Adult females and larvae were fed with Acremonium kiliense and Ambrosiella hartigii, temperature thresholds and thermal constants for development were calculated for the first time,and the effect of temperature on development of the beetle was clarified.The results showed that egg,larva and pupa could complete the development from 16 to 31℃.For egg, larva and pupa stage development,the temperature thresholds were 12.11,10.08 and 11.34℃,the thermal constants were 62.65,189.02 and 86.20 degree-days,respectively.The optimum temperature for larval development was 25.53℃.The effect of light and temperature on X.germanus adult females' take-off was studied in the laboratory.A relative remarkable phototaxis of the adult females was proved.At 25℃,no beetle took off in the dark.Temperature was prerequisite for adult females' take-off,and the threshold temperature was 21℃.Only when temperature reached 21℃, began female adults to take off in the light.The entrance holes excavated by X.germanus adult females mainly distributed in the 0-60 cm high stem,the spatial distribution patterns fitted the negative binomial distribution and belonged to the aggregated pattern both in orchards and within trees,the basic element for the distribution was clusters of individuals,and the individuals attracted each other. These results indicated that aggregatively attack strategy was used to attack grapevine by X. germanus adult females.3 Composition and variety of the ambrosia fungi associated with X.germanus4 species of fungi were isolated from galleries and mycagium.According to the morphological and cultural characteristics,they were identified as Ambrosiella hartigii Batra,A cremonium kiliense Gr(u|¨)tz and two species of Fusarium.The sequence homologies of ribosome RNA gene was also used to identify A.hartigii and A.kiliense.The sequence homologies of 28S ribosome RNA were all 98%when A. hartigii identified by morphology was compared with the sequences of A.hartigii and that of Ambrosiella xylebori retrieved from genebank,whereas that of 18S ribosome RNA were all 99%.The sequence homologies of 18S ribosome RNA between A.kiliense identified by morphology and the sequence retrieved from genebank was 94%.These results indicated that the sequence homologies of ribosome RNA gene could not be used to distinguish A. hartigii from A.xylebori.The composition and the relative dominance of the fungi in the gallery system and in the mycangium of X.germanus varied with developmental stages of the beetle by isolation experiments and scanning electron microscopy.A.hartigii was the only fungus isolated from the mycangia of the dispersal,boring,overwintering and newly sclerotized adults but not the callow adults.The lowest frequency of the fungus isolated from the mycangium occurred in the newly sclerotized adults.The fungi isolated from galleries consisted of A. hartigii,A.kiliense and two species of Fusarium.A.hartigii occurred in a higher percentage of about 40-60%during the period from egg to pupal stage,while A.kiliense and Fusarium sp.1 accounted for 34.6%and 34.6%from the adult galleries,respectively. A.hartigii was always isolated from galleries from the egg to pupal stage.Scanning electron microscopy showed that the conidiophores and conidia of A.hartigii were predominantly occurred at the bottom of galleries from the egg to pupal stage,whereas Fusarium spp.were predominantly occurred in the mature adult galleries.4 Biological characteristics of Ambrosiella hartigii and Acremonium kilienseA.hartigii could produce many spores and grow very well on the PDA and PSA medium.The mannitol carbon source and KNO3 nitrogen source were the best for mycelial growth,while sucrose and glycin was favorable for spore formation.The mycelium could grow between10-30℃,while the spores could form between 20-30℃. For mycelial growth and sporulation,the optimum temperatures was 25℃,the optimum pH was 6.0.The mycelial growth,sporulation and spore germination all need darkness. For spore germination,the optimum temperatures were 24-28℃,pH was 5.0-6.0,the lethal temperature was 46℃(10min).The conidia could not germinate in water.A.kiliense could grow very well on the CMA,PDA and ME medium,and produce many spores on the YEME medium.The lactose and mannitol carbon source,and the peptone,beef extract and glycin nitrogen source were the best for mycelial growth,while glucose and yeast extract were favorable for spore formation.For the mycelial growth and sporulation,the optimum pH was 5.0,the optimum temperatures was 23-25℃.For spore germination,the optimum pH,the optimum temperatures and lethal temperature were 5.0-6.0,24-28℃and 46℃(10min),respectively.Interrelation of A.hartigii,A.kiliense and Fusarium sp.were studied in dual culture. A.hartigii grew faster than the other two species of fungi,and it significantly inhibited the growth of the other fungi.The nonvolatile significantly prevent A.kiliense and Fusarium sp.from growth of aerial hypha.These results indicated that the growth and sporulation characteristics of A.hartigii as well as its prevention from aerial hypha growth of the other fungi made it predominant in the galleries.5 Effect of AmbrosieUa hartigii,Acremonium kiliense and Fusarium sp.on development and reproduction of X.germanusThe effect of A.hartigii,A.kiliense and Fusarium sp.on the X.germanus development and reproduction were studied.The larvae could complete development living on three species of fungi,the larvae grew fastest and had the highstest survival living on A.hartigii,while the larvae grew slowest and had the lowest survival feeding on Fusarium sp..The adult females could reproduce offsprings feeding on three species of fungi,however,its reproductivity feeding on A.hartigii was highest of three species of ambrosia fungi.The nutritional value of A.hartigii,A.kiliense and Fusarium sp.was primarily studied.After ambrosia fungi being cultured 3,5 and 10 d,Ergosterol content in A.hartigii were higher than that in the other fungi.Soluble protein and sugar content in A.kiliense were higher than that in the other fungi.The correlation between nutritional value of ambrosia fungi and development and reproduction of the beetle is to be studied further.
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