Range Expansion Of Liriomyza Trifolii (Burgess) And Competitive Displacement With Its' Congener Species,L.Sativae Blanchard,in China

Biological invasions could cause serious ecological and economic problems,even make a threaten to human health.The non-native species in China include ca.70 microbe species,ca.200 animal species and ca.300 plant species.Most of them are agricultural and forest pests.There are three alien Liriomyza species which have become major pests on vegetable and ornamental crops in China.In this paper,the invading processes,current distribution status and competitive displacement of two congener leafminer species(i.e.L.trifolii and L.sativae,of which invaded China during 2005 and 1994,respectively)were studied.The main results are as follow:Population survey reveals the current distribution of L.trifolii,and found a quite slower range expansion rate in L.trifolii than L.sativae.We newly detected the distribution of L.trifolii in 13 cities,six provinces through the investigation of 76 cities,24 provinces.The comparison results showed that L.sativae rapidly dispersed to and broke out in most provinces of China in the next year following its invasion.But,L.trifolii,after a decade invasion,merely spread from south-east coastal areas to north China plain and caused slight damages.Local species suppressed the L.trifolii population growing through competition and parasitism activities(i.e.biological barrier).The interspecific suppressions between the two leafminer species and the same parasitism rates of indigenous parasitoids on L.trifolii were found.Interspecific interference results showed that the presence of heterospecific individuals would significantly reduce the number of offspring,and the more intruders,the fewer offspring.The interspecific interference could restrict the regional population expansion by reducing their growth rates.During 2014 to 2017,through investigation of their parasitoids in 15 provinces(including more than 40 cities)of China,no differences were found in the comparison of parasitism rates among populations of L.trifolii,L.sativae and mixed L.trifolii&L.sativae.The results indicated that local parasitoids could also parasitize L.trifolii and therefore control its population outbreak.The low temperature in northwest region could not explain the spread restriction of L.trifolii(i.e.biotic barrier).The distribution-restricted leafminer L.trifolii is more cold-tolerant than the widespread L.sativae.The two leafminer species failed to overwinter in field conditions,but were able to overwinter in greenhouses in northern China.The pupae of L.trifolii has a longer survival time than L.sativae in winter fields.Pupae of them could survive over 10 days at 4?(lowest average in greenhouse),about 1 day at-10?(lowest average in fields),but only tens of miniutes at-20? and-40?.These results demonstrated that the pupae of L.trifolii can also persist a longer time at the extreme low temperature.The cold-tolerance proved the colonization,dispersal and distribution potential of L.trifolii at north-west China.L.trifolii is displacing or has displaced L.sativae in considerable regions where they co-exsitence.L.trifolii has become the dominant species in six newly invaded cities and maintains dominant over L.sativae in Hainan province currently.L.trifolii has already displaced L.sativae in the middle and south of Anhui province(Hefei,Maanshan,Wuhu and Xuancheng)and some adjacent areas,such as Huanggang,Hubei province and Xinyang,Henan province.L.trifolii was still in low population or just started invasion in rest region,like Hebei and Shandong Province.Species exclusion was determined by the direct competition on the host plants,but the influence of environmental factors could not be overlooked.In the lab,greenhouse and field cage experiments,the competitive exclusion happened in the two leafminer species excluding the influence of pesticides and parasitoids.The different host plants had different displacement directions.L.trifolii was able to outcompete L.sativae on cowpeas and kidney beans,but the opposite occurred on most treatments involving luffa gourd plants.The same host treatments have the same direction,but different displacement rates and levels.This could be influenced by the initial population proportion and environmental temperature.Reproductive interference could been involved in their competitive displacement process.The convergences and divergences in mating behavior may cause the occurrence and resistance of reproductive interference between the two leafminer species.Almost a thousand times of mating behavior were recorded with self-assembly insect behavior monitoring system.There were no obvious differences in the courtship and copulation process between the two leafminer species.The mating frequency of L.trifolii was significantly higher than L.sativae,yet the mating duration time(20 minutes in average)of the former was around half long of the latter.In addition,L.sativae required higher mating environment conditions.The mating rhythm of the two leafminer flies also differ greatly.In this thesis,we got a clear picture of the invasion and distribution of L.trifolii and tried to explain how the local ecosystem influenced on it.The study illustrated the current status of population displacement in the two invasive leafininer species and primarily explored its internal mechanism.We found a much slower expansion rate of L.trifolii,which could be attributed to the interspecific interactions with L.sativae and indigenous parasitoids(i.e.biotic resistances).In addition,their population displacement were likely mediated by direct resource competition,where reproductive interference could also being involved.These results would be useful for the prediction and management of alien leafininers,and offer case study support for the basic theory study of invasion ecology and sibling competition.