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Discovery of Xylella fastidiosa from olive trees with “Olive quick decline syndrome” in October 2013 on the west coast of the Salento Peninsula prompted an immediate search for insect vectors of the bacterium. The dominant xylem-fluid feeding hemipteran collected in olive orchards during a 3-mo survey was the meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Aphrophoridae). Adult P. spumarius, collected in November 2013 from ground vegetation in X. fastidiosa-infected olive orchards, were 67% (40 out of 60) positive for X. fastidiosa by polymerase chain reaction (PCR) assays. Euscelis lineolatus Brullé were also collected but tested negative for the pathogen. Transmission tests with P. spumarius collected from the Salento area were, therefore, conducted. After a 96-h inoculation access period with 8 to 10 insects per plant and a 30-d incubation period, PCR results showed P. spumarius transmitted X. fastidiosa to two of five periwinkle plants but not to the seven olive plants. Sequences of PCR products from infected periwinkle were identical with those from X. fastidiosa-infected field trees. These data showed P. spumarius as a vector of X. fastidiosa strain infecting olives trees in the Salento Peninsula, Italy.

Cotton leafroll dwarf virus (CLRDV) is a yield-limiting, aphid-transmitted virus that was identified in cotton, Gossypium hirsutum L., in the United States of America in 2017. CLRDV is currently classified in the genus Polerovirus, family Solemoviridae. Although 8 species of aphids (Hemiptera: Aphididae) are reported to infest cotton, Aphis gossypii Glover is the only known vector of CLRDV to this crop. Aphis gossypii transmits CLRDV in a persistent and nonpropagative manner, but acquisition and retention times have only been partially characterized in Brazil. The main objectives of this study were to characterize the acquisition access period, the inoculation access period, and retention times for a U.S. strain of CLRDV and A. gossypii population. A sub-objective was to test the vector competence of Myzus persicae Sulzer and Aphis craccivora Koch. In our study, A. gossypii apterous and alate morphs were able to acquire CLRDV in 30 min and 24 h, inoculate CLRDV in 45 and 15 min, and retain CLRDV for 15 and 23 days, respectively. Neither M. persicae nor A. craccivora acquired or transmitted CLRDV to cotton.

Does Xylella fastidiosa, a bacterial plant pathogen with noncirculative foregut-borne transmission, manipulate behavior of its sharpshooter vector to facilitate its own inoculation? To answer this question, blue-green sharpshooters, Graphocephala atropunctata (Signoret), were reared on basil to clean their foreguts, then removed from the colony and given one of four pre-electropenetrography (EPG) treatments: i) old colony adults on basil, ii) young colony adults on basil, iii) young colony adults held on healthy grapevine for 4 days, and iv) young colony adults held on Xf-infected (symptomatic) grapevine for 4 days. After treatments, stylet probing behaviors were recorded on healthy grapevine via AC-DC electropenetrography. Waveforms representing putative Xf inoculation (XB1 [salivation and rinsing egestion] and XC1 [discharging egestion]) and other behaviors were statistically compared among treatments. Mean number of events per insect and ‘total’ duration per insect of XB1 and XC1 were highest for insects from healthy grape, lowest for basil (regardless of insect age), and intermediate for Xf-infected grape. The surprising results showed that prior exposure to healthy grapevines had a stronger effect on subsequent performance of inoculation behaviors on healthy grapevine than did prior exposure to Xf-infected grapevine. It is hypothesized that non-Xf microbes were acquired from healthy grapevine, causing greater clogging of the precibarium, leading to more performance of inoculation behaviors.This study shows for the first time that presence of noncirculative, foregut-borne microbes can directly manipulate a vector’s behavior to increase inoculation. Also, EPG can uniquely visualize the dynamic interactions between vectors and the microbes they carry.

Prunus necrotic ringspot virus (PNRSV) and prune dwarf virus (PDV) are pollen-borne viruses of important stone fruit crops, including peaches, which can cause substantial yield loss. Although both horizontal and vertical (i.e., seed) transmission of both viruses occurs through pollen, the role of flower-visiting insects in their transmission is not well understood. Bees and thrips reportedly spread PNRSV and PDV in orchards and greenhouse studies; however, the field spread of PNRSV and PDV in peach orchards in the southeastern United States is not explored. We hypothesized that bees and thrips may facilitate virus spread by carrying virus-positive pollen. Our 2-yr survey results show that 75% of captured bees are carrying virus-positive pollen and moving across the orchard while a subsample of thrips were also found virus positive. Based on morphology, Bombus, Apis, Andrena, Eucera, and Habropoda are the predominant bee genera that were captured in peach orchards. Understanding the role of bees and thrips in the spread of PNRSV and PDV will enhance our understanding of pollen-borne virus ecology.

The sharpshooter Cicadella viridis L. (Hemiptera: Cicadellidae) is the most common sharpshooter in Europe and, given its xylem feeding behavior, is considered a potential vector of the plant pathogenic bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae). We tested X. fastidiosa subsp. pauca ST53 (Xfp) transmission capabilities of C. viridis adults, namely 1) acquisition efficiency from four host plant species—periwinkle, milkwort, lavender, alfalfa—and from two artificial diets (PD3 and Xfm), 2) inoculation efficiency to periwinkle at different times post acquisition from different plant and artificial diet sources. The main European vector species—Philaenus spumarius L. (Hemiptera: Aphrophoridae)—was used as a control. C. viridis was able to acquire Xfp from periwinkle, milkwort, and lavender, although with low efficiency (3–16%) and from artificial diets (23–25%). Successful inoculation on periwinkle was extremely rare, being observed only three times, following feeding on milkwort plant and PD3 artificial diet sources. Our study shows that C. viridis is not a relevant vector of Xfp, given the very low transmission rate in controlled conditions, and the inability to feed on olive. The low efficiency reported here correlates with ecological constraints of the vector (mainly monocots host plants, humid environments) that make it difficult to forecast a relevant role in dispersing X. fastidiosa, at least within the present distribution of the exotic bacterium in Europe. However, a possible role of this species in spreading Xf in other agroecosystems, e.g., vineyard and stone fruits grown in humid areas, cannot be excluded.

Whitefly-transmitted Tomato yellow leaf curl virus (Family Geminiviridae; Genus Begomovirus) severely restricts tomato production in the Southeastern United States. Whitefly and tomato yellow leaf curl virus management studies typically investigate control tactics individually, but successful management of this pest complex more often relies on a combination of tactics. This study examined the individual and combined effects of tomato yellow leaf curl virus-resistant cultivars, insecticides, and metallic reflective mulch on whiteflies, tomato yellow leaf curl virus disease incidence, and marketable tomato yields using split-split plot trials over 3 yr. Reflective mulch significantly reduced whitefly adults and nymphs and tomato yellow leaf curl virus symptom severity in all 3 yr of the study. Reflective mulch treatments also provided greater marketable tomato yield in 2 out of 3 yr. Imidacloprid and cyantraniliprole treatments reduced whitefly adults and nymphs' establishment and marginally increased yields, but there was no significant insecticide effect on tomato yellow leaf curl virus incidence/symptom severity compared with the non-treated check. Virus-resistant tomato cultivars did not influence whitefly populations, but provided consistent reduction in virus disease incidence. Interactions between host plant resistance and insecticide treatments ranged from strongly additive in the standard white plastic mulch treatment to only marginally additive in the reflective mulch treatments in terms of enhancing tomato yields. tomato yellow leaf curl virus-resistant tomato cultivars and reflective mulch provided the bulk of the protection against tomato yellow leaf curl virus disease incidence. However, it was the combination of all the best tactics (reflective mulch, cyantraniliprole, ‘Security’ hyb. tomato yellow leaf curl virus-resistant) that provided the maximum increase in marketable tomato yield (2.8-fold) over the least effective combination (white mulch, no whitefly insecticide, ‘FL47′ hyb. tomato yellow leaf curl virus-susceptible).

White-spotted flower chafer adult (Protaetia brevitarsis, Coleoptera: Scarabaeidae), a serious omnivorous pest in regions with multiple fruits and crops, was studied to gain a deeper understanding of its damage patterns. DNA molecular tracking technology was used to identify host plant residues in adult P. brevitarsis midgut, and plant species with the most availability were determined during their growing season. Combining the 2019 and 2021 results, it was found that adults in the multi-cropped area fed on 32 plant species from 23 families, with grape (Vitis vinifera, 40%), peach (Prunus perisica, 23%) and mulberry (Morus alba, 14%) making up the majority of their diet. Some adults fed on multiple plant hosts, with four species detected in one adult and two to three species detected in one-third of adults. Adults shifted among host species during the season, moving from mulberry or grape to peach and then back to grape. These results provide a scientific basis for in-depth research to develop green integrated control technologies against P. brevitarsis adults.

Tomato yellow leaf curl virus (TYLCV) and Tomato chlorosis virus (ToCV) are plant-infecting viruses that are mainly transmitted by Bemisia tabaci Gennadius. In addition to their significant individual impacts on agricultural production, TYLCV and ToCV co-infections are increasingly common and can cause devastating losses in tomato and other crops. Cathepsins, the main proteases in lysosomes, affect both immune responses and the digestion of plant proteins and may help mediate Bemisia-virus-plant interactions. We conducted research exploring the role of cathepsin in the interaction between B. tabaci MED and the plant viruses TYLCV and ToCV, both singly and in combination, on tomato. Levels of cathepsin F increased sharply in B. tabaci MED after feeding on TYLCV-infected, ToCV-infected, and co-infected plants and remained elevated for several days after feeding cessation. In all cases, levels were higher in co-infected B. tabaci MED than in singly infected individuals. Viral loads of each virus were also higher in co- versus singly infected B. tabaci MED, suggesting a synergistic relationship between TYLCV and ToCV. We next studied how dosing B. tabaci MED with a cathepsin inhibitor, inducer, or control affected viral acquisition, retention, and transmission. Viral acquisition and retention were lower in B. tabaci MED treated with cathepsin inducer than in controls; B. tabaci MED treated with cathepsin inhibitor had higher rates of viral acquisition and retention. Viral transmission was highest in the inhibitor treatment and lowest in the inducer treatment. Our results provide more opportunities for the design of novel control strategies to manage insect vectors and their transmitted viruses.

The spread of toxigenic Aspergillus into maize by insects and the subsequent aflatoxin contamination poses a risk to humans and animals and has been investigated in North and South America.To evaluate this effect in an African context, Greenhouse studies were conducted in 2022 to determine the role of sap beetles, Carpophilus dimidiatus Fabricius, 1792 (Coleoptera: Nitidulidae) and maize weevils, Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae) on infection of maize kernels by Aspergillus flavus Link and the resultant aflatoxin accumulation. To test the beetles' efficacy, treatments were applied on partially opened primary ears at 3 different stages of kernel development (BBCH 75, 83, and 87). The treatments were: (i) distilled water, (ii) water with A. flavus spores, (iii) maize grits, (iv) maize grits with A. flavus spores, (v) C. dimidiatus, (vi) C. dimidiatus with A. flavus spores, (vii) S. zeamais, and (viii) S. zeamais with A. flavus spores. Data on kernel infection, maize rotting, yield, and aflatoxin content in kernels were collected. The highest kernel spoilage and yield loss were recorded for the co-inoculation of S. zeamais and A. flavus spores, followed by S. zeamais without A. flavus spores, and then C. dimidiatus with the fungal spores. Inoculation of maize at the BBCH 83 growth stage resulted in the highest kernel damage and aflatoxin contamination. S. zeamais and, to a lesser extent, C. dimidiatus effectively spread the A. flavus inoculum into non-wounded ears, resulting in fungal and aflatoxin contamination.The yield loss from S. zeamais-Aspergillus co-inoculation occurred due to the grain rotting and actual feeding of the maize weevils.Thus, insect management is important in reducing pre-harvest contamination of maize with mycotoxigenic fungi and their resultant toxins. Graphical Abstract

The Asian citrus psyllid, Diaphorina citri Kuwayama, is the vector of the bacterial pathogen, Candidatus Liberibacter asiaticus, which is the causal agent of huanglongbing (HLB) in the United States. Both short-range and long-range dispersal of D. citri adults affect the spread of HLB; however, little is known about the long-range dispersal capabilities of D. citri in the field or the seasonality of flight behavior. In the present study, an in situ protein marking technique was used to determine the dispersal of D. citri by trapping marked adults under natural field conditions. D. citri movement from abandoned citrus groves to adjacent managed citrus groves was greatest during the spring and summer months and decreased significantly during the colder months (September–March). D. citri were able to traverse potential geographic barriers such as roads and fallow fields. In an experiment conducted to determine long-range dispersal capacity in the absence of severe weather events, D. citri were able to disperse at least 2 km within 12 d. Wind direction was not correlated with the number of marked psyllids captured, indicating substantial flight capability by D. citri. Finally, the number of marked psyllids captured increased with the density of emerging young leaves on surrounding trees. The results confirm that abandoned citrus groves in Florida serve as reservoirs for D. citri, which can disperse across long distances despite geographical barriers.