Tomato yellow leaf curl virus (TYLCV) and its vector insect, the sweet potato whitefly Bemisia tabaci, are major threats to tomato and pepper production in all around world. Since the last three decades, both B. tabaci and TYLCV have been invaded into many countries via different routes. Our studies showed that various geminiviruses including TYLCV can be transmissible by seeds as well as whiteflies. Furthermore, commercially developed resistant tomato strains against TYLCV infection can serve as TYLCV reservoirs and potentially influence on TYLCV epidemics. Therefore, transmission pathways through both insect vectors and seeds should be concerned for suitable management of geminiviruses and whiteflies.

Vector-borne plant virus transmission is a complex mechanism. Plant viruses modify development and behavior of vectorinsects in a positive, negative, or neutral manner. Bemisia tabaci transmits Tomato yellow leaf curl virus (TYLCV) whichis a virus that seriously damaged tomato cultivars all around the world. We compared several behavioral and physiologicalcharacteristics between non-viruliferous (NV) and TYLCV-viruliferous (V) of whiteflies. When B. tabaci acquired TYLCV,total life span was shorter and fecundity was lower than NV ones. V whiteflies were more susceptible to thermal stressby increasing hsp mRNA levels but higher in mortality by either heat or cold shocks. Further, V whiteflies increasedthe rates of plant sap probing and light attraction behaviors than NV ones. Our results provide insights to understandvector’s role in relation to the acquisition and transmission of plant viruses.

Tomato yellow leaf curl virus (TYLCV) causes a highly serious disease in tomatoes in many countries. The most important thing in management is the prevention of virus transmission. TYLCV had been known to be only transmitted by a vector, the sweetpotato whitelfy, Bemisia tabaci. However, we identified two other important routes of TYLCV transmission into tomatoes. It is seed-transmissible. Many seeds available in domestic and global markets were infected by TYLCV. It is also infective into various weeds and other horticultural crops and transmit virus through vector insects. Therefore, we need a new strategy for the virus and vector management.

Glucose-regulated protein 78 (GRP78) is a member of the heat shock protein 70 (HSP70) family that is specific to endoplasmic reticulum (ER). It is known as chaperones and signaling regulators that respond to ER stresses in vertebrates. However, its function in invertebrates, including insects, is uncertain. Here we determined a full cDNA sequence and the expression patterns of grp78 of Aphis gossypii, which is a major pest of numerous crop plants worldwide. Its cDNA had highly conserved motifs of the HSP70 family and the C-terminal motif of KDEL characteristic of ER-specific HSPs. It showed 98.5% identity with the GRP78 of the pea aphid Acyrthosiphon pisum. Real-time RT-PCR analysis showed that the grp78 level was higher in the fourth instar nymph than in the younger instar and adult stages. Its level was not affected by thermal stress of 10 to 40°C for 1 h. The grp78 level was proportional to the ingestion of a sucrose solution ranging in concentration from 0% to 30% in a Parafilm feeding chamber. In addition, the grp78 level varied among aphids feeding on leaves from 14 different host plants for 24 h; it was higher with eggplant and pepper but lower with pigweed and tobacco than any other plants. Our study suggests that the grp78 level is regulated by nutritional condition of A. gossypii.

Heating for disinfestation has been practiced of at the condition of 55-60°C for at least 48 hours in various facilities of stored and processed agricultural products. However, it has been required to reduce temperature and time due to the economic efficiency. To improve disinfestation efficiency of heating, we demonstrated whether combined treatments of heat with other agents exert synergistic for disinfestation. Heat treatments were combined with 1 ppm diatomaceous earth (DE), 10 ppm phosphine or 10% carbon dioxide against Plodia interpunctella, Sitophilus zeamais and Tribolium castaneum. Insects were treated single or multiple combinations of each component for 6 h at either 25°C or 40°C, then mortalities were monitored for 14 days post-treatments. Combined treatments greatly enhanced mortalities and shorten killing time of three species rather than single treatments. Particularly, heat treatments with 1 ppm DE and 10 ppm phosphine completely lethal within 3-6 h post-treatments, but heating with 10% CO2 was not much effective. Among three species, S. zeamais adults were more suscpetable to heat but both larvae and adults of T. castaneum was highly susceptible to phosphine. Our results clearly showed that combined treatment of DE or phosphine with mild heating (40°C) greatly improved mortalities of three major stored pest insects and provide advanced techniques for disinfestation of stored product pests.

The effects of a newly developed flower thinning formulation (FTF) on the vitality of the honey bee Apis mellifera were examined by measuring the activities of various digestive enzymes in adult worker bees. First, direct spraying of the FTF solution did not cause any behavioral changes or lethal effects for the honey bees based on 24 h observation. Second, oral ingestion of a sugar solution containing the FTF did not produce any significant change in the activities of amylase, proteinases, lipase, or acetylcholine esterase (AChE) in the worker bees 6 h or 24 h after treatment. Meanwhile, a commercial formulation containing sulfur compounds showed slightly reduced activities for several digestive enzymes and AChE, although no behavioral disturbance. Thus, the results of the present study suggest that the FTF is not toxic for honey bees, in terms of contact and ingestion. Therefore, this newly developed FTF can be used for flower thinning without any detrimental effects on pollinating insects.

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.

Sweetpotato whitefly, Bemisia tabaci, is a vector of more than 100 plant-diseased viruses, as well as a serious pest of various horticultural plants. This species harbors a primary endosymbiont Portiera along with several secondary endosymbionts such as Cardinium and Hamiltonella. We investigated whether or not TYLCV acquisition alters the densities of endosymbionts in the body of B. tabaci using quantitative real-time PCR. Our results showed that the densities of both Cardinium and Hamiltonella, but not Portiera, increased upon acquisition of TYLCV. In addition, expression of GroEL, a molecular chaperone produced by Hamiltonella, was significantly upregulated in TYLCV-infected whiteflies. Our results suggest that endosymbionts may play an important role in TYLCV transmission mechanism within the body of B. tabaci.

Whiteflies harbor several secondary endosymbionts, which are maternally inherited from mother to offspring, that have major effects on host preferences, biology, and evolution. Here, we identified Wolbachia bacteria in sweetpotato whitefly (Bemisia tabaci) as well as whitefly popluations from other countries by comparison of 16S rDNA sequences. Wolbachia were detected in all tested indigenous B. tabaci populations (Bangladesh, Myanmar, Nepal, and the Philippines) as well as Q1 biotype of Korea, whereas they were absent from B biotype of Korea and Q biotype of China. Wolbachia were also detected in all five tested Aleurodicus dispersus populations as well as Tetraleurodes acaciae, whereas they were not detected in all seven Trialeurodes vaporariorum populatuions. In addiiton, Wolbachia were detected in parasitic wasp (Encarsia formosa) of B. tabaci as well as honeybee (Apis mellifera). Among the 19 whitefly populations from different countries, our analysis identified four phylogenetic groups of Wolbachia, thereby demonstrating the high diversity of this genus. Wolbachia phylogeny suggests a correlation of geographical range with ecological variation at the species level.

Recently, several significant plant virus diseases have devastated various crops in agricultural fields of Korea, These virus disease are mostly transmitted and spread by vector insects, such as rice stripe virus (RSV) transmitted by planthopper Laodelphax striatellus, tomato spotted wilted virus (TSWV) by thrips Frankliniella occidentalis and tomato yellow leaf curl virus (TYLCV) by whitefly Bemisia tabaci. Insects as vectors are significantly important for the control of plant disease as well as insect themselves. Here, on the view of insects, interactive mechanisms of vector insect and plant pathogens were discussed on the system of TYLCV and B. tabaci. When insects acquisited virus they would be beneficial, neutral or detrimental. Generally, plant virus are ingested into the mouse and move from the gut to hemolymph and back to salivary gland. During this movement there would be numerous molecular interactions at a vector-virus specific mode. In addition, virus acquisition change vector's physiological and developmental states including longevity, fecundity and dispersal behavior. However, these interactive mechanisms of vector insects with plant virus are largely under investigated. B. tabaci is genetically diverse and transmit many begomoviruses including TYLCV. I demonstrated effects of TYLCV acquisition on fecundity, thermal response, endosymbiont profile and gene expression of B. tabaci.

The sweet potato whitefly Bemisia tabasi is one of the most important pests of various horticultural crops. In addition, B. tabaci is a vector of many plant-pathogenic viruses and cause a serious secondary damage to crop plants. Association of plant-pathogenic virus with vector insects is known to be effective on the transmission capacity, fecundity, longevity of vectors including whiteflies. However, the interactive mechanisms between virus and vector insects are still poorly understood. Recently, a serious damage caused by virus disease together with B. tabasi emergence was identified at tomato glasshouse in Tongyoung. We detected the signals of Tomato Yellow Leaf Curl Virus (TYLCV) in tomato leaves and vector whiteflies using PCR amplification and confirmed its presence by those sequence comparison. To determine the effects of TYLCV acquisition on physiological status of vector whiteflies, transcript levels of genes that associated with metamorphosis, metabolism, stress and immune processes were compared between TYLCVinfected whiteflies and non-infected ones. Generally, the transcript levels of virus-infected whiteflies were lower than those of non-infected ones. In addition, the associations of endosymbiont levels within whiteflies were discussed in aspect of the acquisition and transmission of TYLCV.