Distribution Of Lymantria Xylina Egg Masses And Effects Of Extreme Environmental Factors

The moth Lymantria xylina(Swinhoe)is a serious forestry pest in eastern coastal areas of China.The insect has complex diet,and can endanger 424 species of plants belonging to 103 families.In order to provide a basis for the risk assessment of L.xylina spread,we investigated the distribution characteristics of L.xylina egg masses in the coastal Casuarina equisetifolia through field system surveys and geostatistical analyse method,and studied effects of extreme high temperature,extreme low temperature and salt solution stress on the survival of L.xylina egg masses through laboratory tests.The main results are summarized as follows:(1)The spatial distribution characteristics of L.xylina egg massesIn Casuarina equisetifolia forest of Pingtan,Fujian,the horizontal distribution type of L.xylina egg masses are clustered distribution,and the egg mass has a strong spatial agglomeration.The agglomeration center is obvious,concentrated in the woodland center on the side of the leeward,and spreaded from the central plant to the whole forest area.In addition,L.xylina egg masses are mainly distributed on the fine lateral branches of Casuarina equisetifolia,a small amount produced on the undergrowth plants or other vegetation and objects on the edge of the forest.A total of 12 plants belonging to 11 families and 2 objects were found to have egg masses.The distribution characteristics of L.xylina moth egg masses are closely related to their own behavior characteristics.The low age larvae have the habit of avoiding the wind and avoiding sunshine and taking the tender leaves of the young shoots.The old larva has a strong crawling ability and the high density will be transferred to the adjacent plants.The female moth is large,and the activity is weak,and usually lays eggs near the pupal shell.(2)Effects of extreme high temperature stress on the survival of L.xylina egg massesThe stress temperature and duration all had significant effects on the survival of L.xylina egg masses,and its mortality increased with the increase of temperature and duration.Ltimeso of L.xylina egg masses at 30?45 ? was 16.60 d,14.31 d,1.33 d and 1.17 d respectively.When the stress duration was 3 h,5 d,10 d and 15 d,LHT50 of L.xylina egg masses was 46.80 ?,36.52 ?,36.46 ? and 31.82 ? respectively.The tolerance period at 40 ? and 45 ? was less than 3 h,and 50 ? was the upper limit of the tolerance to high temperature of L.xylina egg masses.Almost no individual survives in a very short period of time.(3)Effects of extreme low temperature stress on the survival of L.xylina egg massesThe low temperature intensity and duration all had significant effects on the survival of L.xylina egg masses,and its mortality increased with the decrease of temperature and duration.Ltimeso of L.xylina egg masses at 0 ??-5 ??-10 ? was 28.26 d?8.59 d?2.08 d respectively.When the stress duration was 1 d,5 d,10 d,15 d,20 d,25 d,LLTso of L.xylina egg masses was-13.21 ?,-6.85 ?,-6.33 ?,-4.91 ?,-4.43 ?,1.35 ? respectively.50 ? was the upper limit of the tolerance to high temperature of L.xylina egg masses.Almost no individual survives in a very short period of time.The mortality rate at-15 ? for 1 day was 90.8%,and almost no individuals survived at-20 ?.(4)Effects of salt solution stress on the survival of L.xylina egg massesL.xylina egg masses has strong resistance to salt water immersion stress.Low salinity and short-term treatment had little effect on the survival of L.xylina egg masses.Pure water(0‰)had no effect on the mortality rate within 17 days of immersion,but high salinity and long-term treatment had a greater effect,under salt water of 35-54.2‰ salinity.After 15 days of treatment,the mortality rate was about 80%.Salinity treatment and treatment time all had significant effects on the survival of L.xylina egg masses,but the interaction between the two was not significant.In general,the mortality of L.xylina egg masses increased with the increase of salinity and treatment time.At the 1 d,3 d,5 d,8 d,9 d,11 d,13 d,15 d,and 17 d treatment time,the half lethal salinity were 101.10‰,67.23‰,36.79‰,42.55‰,61.90‰,38.18‰,31.68‰,28.61‰,16.45‰,respectively.under the salinity treatment of 9.4‰,28.6‰,35‰,41.4‰,47.8‰,54.2‰,the median lethal time was 30.22d,10.32 d,9.42 d,9.19 d,4.89 d,7.88 d respectively.Half lethal salinity was generally reduced gradually with the increase of treatment time,and median lethal time gradually decreased as the treatment salinity increased.