Study On The Occurrence Regulation And Control Techniques Of Hylobitelus Xiaoi Zhang In Western Fujian

The dangerous insect pest of pine,Hylobitelus xiaoi Zhang was found and had made badly damages in all seven counties of the Western Fujian except of Meihua Mountain Nature Reserve in recent yeras.Especially,its host-infested ratio in Shang-hang,Wu-ping and Chang-ting reached 45%, higher than that in the other counties.The pest population shows a spreading and aggravate tendency in these areas at present.Some damaged pine trees were dead,but more trees became weak,due to the parasite of the larva of H.xiaoi.The damage ratio of H.xiaoi in Pinus elliottii and P.taeda forests were significantly higher than Pinus massoniana.The pest larvae parasitized the base of the pine stem from 0 to 30 cm mainly with the proportion of 60.29%,and few above 50 cm.The most larvae infested the Pinus massoniana of 8 to 12-years-old mainly,and led to the most serious damages for the pine with 11-17 cm diameter.The ratio of infested tree was the highest in the pure Pinus massoniana forest.Meanwhile,this ratio showed a increasing tendence with the increasing of the P.massoniana proportion in the mixed forest. As a whole,the ratio in pure P.massoniana forest was remarkably lower than in the pine forest mixed with broad-leaved trees.The slope aspect showed no significant effects on the pest population,but slope site showed significant effects,which the infested ratio in mid and low slopes were all extremely higher than in upslope.By means of weeding one or two times a year,the revised decrease rate of the pest reached 39.98%and 51.33%respectively after a year,which were all more than the contrastion significantly. However,the treatrment of two times a year showed a better effect which dropping of rate infested tree was 42.30%.The ratio of infested trees of H.xiaoi was extremely remarkable decrease after one year by manual digging boring tunnel,which corrected dropping of rate infested tree was 78.28%and persistent effectiveness was 75.45%after two years.By injecting trunks and applying on soil with different concentrations of omethoate,methamidophos and dichiorvos,the results showed it got a better efficacy with 5 times liquid of 40%omethoate to injecting trunks,its corrected mortality was 23.59%after twenty days.And general effect was not good by applying on soil.The virulence of five Beauveria bassiana strains was selected test to H.xiaoi adults,,the result showed that the SB1 strain had stronger virulence and higher average spore yield of individual insect.By spraying with(1.0±0.5)×10⁸ conidia per ml of SB1 strain suspension,the corrected mortality and infection rate were(59.09±0.78)%and(57.3±1.38)%respectively after 30 days. It's median lethal times(LT₅₀)were 15.77 days with the average spore yield of individual insect was from(1.07±0.09)×10⁷ conidia per individual.Dose regression equation is y=(0.1292±0.0317)x-(0.3670±0.2586),R=0.9912.The median lethal concentration(LC₅₀)was determined at 5.13×10⁶ conidia per ml.The average spore yield was(1.67±0.56)×10⁸ conidia per cm on non-woven fabrics of SB1 strain in SDAYmedium.The results of laboratory test with non-woven fabrics of SB1 strain indicate that the corrected mortality and infection rate were 52.13%and 46.33% respectively after 30 days,and median lethal times(LT₅₀)were 19.70 days.The results of forest infection test by spraying with(1.0±0.5)×10⁸ conidia per ml of SB1 strain suspension indicate that the mortality was higher than control significantly after 30 days.The corrected mortality and infection rate were 45.79%and 43.33%respectively with the average spore yield of individual insect was(1.15±0.11)×10⁶ conidia per individual.By forest controlling with non-woven fabrics of SB1 strain,the dropping of rate infested tree was 26.58%.It was extremely remarkable lower than control.These results suggest that the SB1 strain could be incorporated into an integrated control programme for the biological control of H.xiaoi.