Climate change has made outbreaks of insect-transmitted plant viruses increasingly unpredictable. Understanding spatio-temporal dynamics of insect vector migration can help forecast virus outbreaks, but the relationship is often poorly characterized. The incidence of Beet curly top virus (BCTV) was examined in 2,196 tomato fields in California from 2013-2022. In addition, we experimentally showed dispersal of the beet leafhopper, the only known vector of BCTV is negatively correlated with plant greenness, and we estimated spring migration timing using a vegetation greenness-based model. Potential environmental factors and spring migration time of beet leafhoppers were associated with BCTV incidence. We found BCTV incidence is strongly associated with spring migration timing rather than environmental factors themselves. In addition, the vegetation greenness-based model was able to accurately predict the severe BCTV outbreaks in 2013 and 2021 in California. The predictive model for spring migration time was implemented into a web-based mapping system, serving as a decision support tool for management purposes.

소나무재선충병의 방제를 위한 나무주사는 살선충제를 사용하여 예방적인 측면에서 이루어 졌다. 본 연구는 소나무에 살충제를 나무주사하여 약제를 소나무 전체에 침투 이행시킨 후 우화한 매개충이 후식하는 과정에서 약제가 포함된 신초를 섭식하게 되면 소화중독으로 교미 및 산란 전에 살충시킴으로서 매개충을 방제하고자 실시하였 다. 이러한 살충제 나무주사 방법은 신초를 후식하는 하늘소류만을 소화중독에 의해 살충시키는 방법으로 기존의 항공방제에 비해 환경에 대한 영향을 최소화 할 수 있다. 살충제 나무주사에 가장 적합한 약제 선발을 위해 실내에서 Neonicotinoid계 살충제 7종을 각 2,000배로 희석한 후 솔수염하늘소에 2㎕를 경구투입하여 살충효과를 평가한 결과 Clotianidin SL, Thiamethoxam DC이 소화중독에 의한 살충효과가 가장 우수하였으며, 이들 살충제를 야외에서 소나무에 나무주사 후 가지에 망대를 설치하고 솔수염하늘소를 접종하여 살충력을 검정한 결과 Thiamethoxam DC가 살충력이 가장 우수한 것으로 판단되었다. 또한 현장적용을 위해 잣나무림에 나무주사후 산란유인목을 설치하여 무처리구와 비교한 결과 살충제 나무주사 시험지의 산란유인목에서는 산란이 이루어지지 않아 현장방제에 적용 가능성을 확인할 수 있었다.

The nematode Bursaphelenchus xylophilus and its vector insect Monochamus alternatus are major quarantine pests of timber products in Korea. Due to the phaseout of methyl bromide as a fumigant for plant quarantine and pre-shipment treatments, the need for an alternative fumigant is essential. Based on preliminary studies on the efficacy of ethanedinitrile (C2N2) to these two pests, three quarantine trials on logs covered with PVC-tarpaulins were conducted at three dosages and three temperatures potential for inhalation exposure was assessed by monitoring atmospheric levels of C2N2 in relation to the threshold limit value (TLV, 10 ppm, v/v). Concentration × time products (Ct) of 398.6, 547.2 and 595.9 g h m-3 were obtained for each quarantine trial. A 100% mortality of B. xylophilus and M. alternatus larvae at 23±4°C and 10±4°C occurred with a load factor of pine logs of 46% and at 3±1°C with a load factor of 30%. During all fumigant procedures, atmospheric levels of C2N2 20m downwind from the PVC tarpaulin were below the TLV. During aeration, levels 10 m and 5 m downwind were below the TLV after a maximum of 0.4 h and 1 h, respectively. For the purpose of an emergent quarantine or phytosanitary treatment, specific doses of C2N2 at the temperatures that occurred during fumigation could control B. xylophilus and M. alternatus larvae without significant inhalation risk to workers.

In this study, we isolated and identified an aggregation-sex pheromone from Monochamus saltuarius, the major insectvector of the pine wood nematode in Korea. Adult male of M. saltuarius produces 2-undecyloxy-1-ethanol, which is knownto be an aggregation-sex pheromone in other Monochamus species. We performed field experiments to determine the attractivenessof the pheromone and other synergists. More M. saltuarius adult beetles were attracted to traps baited with the pheromonethan to unbaited traps. Ethanol and (-)-α-pinene interacted synergistically with the pheromone. Traps baited with pheromone+(-)-α-pinene+ethanol were more attractive to M. saltuarius adults than traps baited with pheromone, (-)-α-pinene, or ethanol alone.Ipsenol, ipsdienol, and limonene were also identified as synergists of the aggregation-sex pheromone for M. saltuarius adults.

The interactions of vector-virus-plant have important ecological and evolutionary implications. In this presentation, I will use the case studies on the whitefly vectors, begomoviruses, and plants to illustrate the complexity, consequences and mechanisms of this type of tripartite interactions. The interactions between begomoviruses and their whitefly vectors via their shared host plants can be mutualistic, neutral or negative depending on the species/strains of each type of the organisms involved. With regard to the mechanisms of plant-mediated positive effects of the viruses on whiteflies, three case studies indicate that suppression of jasmonic acid/salicylic acid related plant defence plays an important role. Our recent studies show that the order of arrival of the interacting vector insects and viruses on the plants may also alter the physiological feature and consequences of the interactions. Future efforts in this area should try to expand the number and diversity of case studies in order to reveal the patterns of interactions, to unravel the molecular and biochemical mechanisms of the interactions using a multidisciplinary approach, and to examine the virus-plant-vector interactions in the field and in natural plant communities.

Since first reported in 1988 the Pine Wilt Disease has been established and spreaded nearly nationwide in South Korea, causing tremendous economic damage in pine forests. The pine wilt nematode (Bursaphelenchus xylophilus), causing the Pine Wilt Disease, in Korea is known to be transported by two insect vectors that are Monochamus alternatus Hope and Monochamus saltuarius Gebler. Currently the pest management strategy largely relies on pesticide application and infected tree clearing. The aim of the present study was to search for early larval parasitoids of M. alternatus using the sentinel log infested with the cerambycid eggs. Only one braconid species was collected and identified as Spathius verustus Chao. Two to ten wasp larvae attached and fed on one host larva. Parasitism rate was 55.5 to 59 % in Jinju site, while 1 to 18.1 % the other sites. Sex ratio was female-biased (female : male = 18.9 : 1). The S. verstus has potential to be use as parasitic natural enemy of M. alternatus.

The sweetpotato whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a disastrous pest in horticultural plants worldwide. B. tabaci is a species complex including at least 24 biotypes in the world. In Korea, B-biotype has been invaded in 1998, Q-biotype in 2005 and widely spread into the country. B. tabaci is also a vector of more than 100 plant viruses, especially begomoviruses. Since 2008, Tomato yellow leaf curl virus (TYLCV) has been invaded into Korea and severely damaged tomato cultivar in all over of the country. B. tabaci is the only vector insect of TYLCV. Here we demonstrated whether TYLCV influence on the vector physiology during virus transmission. Pesticide susceptibility of whiteflies on TYLCV acquisition was determined in B. tabaci using the two-layered parafilm feeding chamber which containing 20% sugar solution including different doses of imidacloprid. Our result showed that TYLCV-viruliferous whiteflies were more susceptible to imidacloprid ingestion than non-viruliferous whiteflies. This study suggests that plant virus can manipulate the physiological conditions of vector insects.

Oak wilt disease caused by Raffaelea quercus-mongolicae was firstly reported at Sungnam city, Gyeonggi province, Korea, in 2004, and spread to several area of Korean peninsula. Raffaelea quercus-monglicae was transferred by ambrosia beetle, Platypus koryoensis, and caused oak wilt disease. Because oak wilt disease is mediated by ambrosia beetle, Platypus koryoensis, control of this disease concentrates on managing the ambrosia beetle population. Until now, several control methods such as felling and fumigation of dead oak trees with metham sodium, sticky-roll trap for catching emerged or attacking beetles, and oak tree logs for attraction of ambrosia beetle have been mainly used to control oak wilt disease in Korea. Although effective, current control methods have many side effects. Felling of oak tree is very difficult and dangerous to workers. To reduce the side effects of conventional control methods, new and safe types of control method for managing the ambrosia beetle populations are essential. In this study, we investigated the number of caught beetles, effect of height and direction of collection bottles by using newly developed mass capturing device for P. koryoensis to evaluate the effectiveness of this device as practical use in field.

Acquisition of plant viruses has various effects on physiological mechanisms in vector insects. Bemisia tabaci is the only known vector of Tomato yellow leaf curl virus (TYLCV), which is a serious virus affecting tomato cultivars. In this study, the lifespan of Q1 biotype was compared between non-viruliferous (NV) and TYLCV-viruliferous (V) whiteflies. Total lifespan from egg to adult death of NV whiteflies was 62.54 days but 10.64 days shorter in V whiteflies. We investigated the temperature susceptibility of B. tabaciby comparing mortalities as well as heat shock protein (hsp) mRNA levels between NV and V whiteflies. For this, NV and V whiteflies were exposed for either 1 or 3 h at 4, 25, and 35 °C. The mortality of V whiteflies was higher than NV ones following exposure at either 4 or 35 °C, but there was no significant difference at 25 °C. Analysis of the expression level of heat shock protein (hsp) genes using quantitative real-time PCR showed that both cold and heat shock treatments stimulated higher expression of hsps (hsp40, hsp70, and hsp90) at various rates in V whiteflies than NV ones, but there was no difference at 25 °C. All together, our results show that TYLCV acquisition accelerated the developmental rate and increased susceptibility to thermal stress in B. tabaci. Therefore, this modification may result in reduced vector longevity due to increased metabolic energy utilization. Our results provide insights into the complex interaction between vector fitness and thermal stress in relation to the acquisition and transmission of plant viruses.

Pine wilt disease, caused by pine wood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, has become the most serious threat to pine trees in Korea since first reported in 1988. Pine wood nematode is transferred to uninfested trees by Monochamus alternatus (Coleoptera: Cerambycidae) (vector). A typical controlling method against vectors in Korea is fumigation of the dead trees infested by vector M.alternatus and B.xylophilus using metam-sodium SL(25%). However, this method is harmful to the environment because of the chemical contamination and vinyl waste in the mountain afterward. Portable Bark Remover (PBR) was contrived to reduce these environmental problems. The vectors oviposite under the bark of the freshly dead trees only. Debark infested trees prohibited the vectors from oviposite and finally, vectors can not complete their life cycle. The PBR is a newly designed as a debarking device that is equipped on top of the chain saw engine allowing ease and rapid debarking of the infested trees at the controlling field. Debarking of freshly-dead trees can eliminate egg-laying and hatch places where between the wood and bark from vectors. The new method for vector controlling using the debarking device is expected to lower-price and high-efficiency comparing with other conventional methods such as “crushing”, “burning” and “fumigation”.

In many cases over the years, we failed to forecast accurately outbreak of Rice stripe virus (RSV) disease using population density of overwintering small brown planthopper (SBPH), Laodelphax striatellus. What is the source of error in this viral disease assessment? For answering the question, spatial distribution of RSV in paddy fields was investigated in relation to the yield of rice grain, and the population density of overwintering SBPH in ridge of paddy fields. Total 14 paddy fields in 5 regions were surveyed in June, 2008. Disease assessment was carried out with each of 30 rice plants in the one of the borders, 5th, 10th line from ridge, and 90 rice plants in diagonal line for conventional method. The ears of rices from 18 plants in the same surveyed line were collected in the late of August for the weights of 100 rice grains. The infection rate of RSV was decreased by the distance from ridge; on the contrary, the increase tendency was shown in the yield of rice grains in the middle of paddy field. It is suggested that the border effect of viral distribution between ridge and paddy field is caused by the spatial distribution of the vector insect. Thus, in this case, the narrow border effect could represent that the SBPH migrated short distance from the ridge to paddy field. The conventional method, observing the disease in middle area of diagonal line, showed no correlation to the population density of overwintering vector generation in ridge. It might cause underestimation of the regional disease rate. The counting of RSV-diseased plant in border line only overestimated it also. However, the RSV infection rate in the near border had highly positive linear relationship (R2=0.91) to the regional average values by regression analysis. Therefore, the near border sampling method can improve the RSV disease risk assessment.