Tomato yellow leaf curl virus manipulates Bemisia tabaci, MEAM1 both directly and indirectly through changes in visual and volatile cues.

The sweetpotato whitefly, Bemisia tabaci MEAM1, is one of the most devastating pests of row-crop vegetables worldwide, damaging crops directly through feeding and indirectly through the transmission of many different viruses, including the geminivirus Tomato yellow leaf curl virus (TYLCV). Y-tube olfactometer tests were conducted at different stages of TYLCV infection in tomatoes to understand how TYLCV affects B. tabaci behavior. We also recorded changes in tomato hosts' color and volatile profiles using color spectrophotometry and gas chromatography-mass spectrometry (GC-MS). We found that the infection status of B. tabaci and the infection stage of TYLCV influenced host selection, with uninfected whiteflies showing a preference for TYLCV-infected hosts, especially during the late stages of infection. Viruliferous B. tabaci attraction to visual targets significantly differed from non-viruliferous B. tabaci. Late-stage infected hosts had larger surface areas reflecting yellow-green wavelengths and higher emissions of methyl salicylate in their volatile profiles. These findings shed new light on several critical mechanisms involved in the viral manipulation of an insect vector and its economically important host.

Cold acclimation increases Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae) survival during exposure to freezing temperatures.

The Asian citrus psyllid, Diaphorina citri, is the vector of the pathogenic bacteria that causes Huanglongbing, the most devasting disease affecting citrus worldwide. As cultivation of citrus tends to expand northward, the tolerance of psyllids to freezing temperatures needs to be investigated. While mortality of D. citri to cold temperature has been previously studied, much less is known regarding the acclimation potential of psyllids to cold temperatures. We first evaluated cold resistance of D. citri depending on color morph and sex. Subsequently, we compared mortality of D. citri at -4 °C for 10 hours between unacclimated psyllids, psyllids that were gradually acclimated to cold over 1 or 2 weeks, and psyllids intermittently acclimated also for 1 or 2 weeks. We did not find major differences in cold resistance between color morphs and sex. We found that after 1 week of gradual acclimation, the survival of psyllids at -4 °C increased to 86%, compared to 20% in the control group. Survival did not increase after the second week of gradual acclimation. Although intermittent acclimation improved survival compared to the control group, it was less effective than gradual acclimation with a survival at 30% and 70% after 1 and 2 weeks of acclimation, respectively, although this difference with gradual acclimation was not significant at week 2. These data show that gradual cold acclimation allows D. citri to survive brief periods below freezing. It may serve as a mechanism responsible for increasing northern establishment of this pest.

Distribution, Phenology, and Overwintering Survival of Asian Citrus Psyllid (Hemiptera: Liviidae), in Urban and Grove Habitats in North Florida.

Cold hardy citrus is an emerging industry in north Florida. However, it is under the threat of Candidatus Liberibacter asiaticus (CLas), the agent of the citrus disease huanglongbing. Distribution and phenology of the Asian citrus psyllid, Diaphorina citri (Kuwayama), the vector of CLas, was investigated over a 2-year sampling period in north Florida. Diaphorina citri was only found in backyard and ornamental citrus along the Gulf of Mexico, and was not observed in cultivated citrus groves during the 2 years (2017-2018) of the survey. Diaphorina citri population peaks occurred approximately 2 mo later than in central Florida with major population peaks occurring in July. The number of D. citri adults was significantly higher on CLas infected than uninfected citrus trees, whereas more nymphs were found on uninfected trees. Most D. citri were negative for CLas except in Franklin county where both infected trees and psyllids were found. We were able to find adult D. citri during all winter months, despite temperatures as low as -5.5°C. During two consecutive winters, we conducted experiments to determine D. citri cold hardiness by caging D. citri under ambient conditions in mid-November and assessing survivors in the following spring. In 2018, approximately 21%, of D. citri adults survived overwintering whereas 16% survived in 2019 despite lower temperature in 2018 than in 2019. As we are at the earliest stage of HLB infestation, management of D. citri and CLas in north Florida should focus on removal of CLas-infected trees to reduce the reservoir of pathogen.