Probing behavior of the leafhopper analyzed through DC electropenetrography and microscopy

Yamatotettix flavovittatus Matsumara is a new leafhopper species vector of sugarcane white leaf (SCWL) phytoplasma that causes sugarcane chlorosis symptoms. The effects of probing behavior of Y. flavovittatus on sugarcane and its implication for SCWL phytoplasma transmission are yet to be studied. In this research, we used DC electropenetrography (EPG) to define waveforms produced by adult and fifth-instar nymphal Y. flavovittatus on sugarcane and correlated them with salivary sheath termini (likely stylet tip locations) via light and scanning electron microscopy. The following six waveforms and associated activities are described: (NP) non-probing, (Yf1) stylet probing into epidermal cells, (Yf2) stylet probing through mesophyll/parenchyma, (Yf3) stylet contact with phloem and likely watery salivation, (Yf4) active ingestion of sap from phloem, probably sieve elements, and (Yf5) unknown stylet activity in multiple cell types. Study findings reveal that the Y. flavovittatus vector ingests sieve tube element more frequently and for longer durations than any other cell type, supporting that Y. flavovittatus is primarily a phloem feeder. Adult Y. flavovittatus show a longer total probing duration and produces a high density of puncture holes on sugarcane leaves. Moreover, probing behaviors revealed that adults typically ingest phloem sap more frequently and for longer durations than fifth-instar nymphs, enhancing sap ingestion. Furthermore, we propose that adults are more likely to acquire (during Yf4) and inoculate (during Yf3) higher amounts of phytoplasma than fifth-instar nymphs. This information on the penetration behavior of leafhopper Y. flavovittatus serves as a basis for advanced studies on the transmission mechanism of SCWL phytoplasma.

Evaluation of the Physical Characteristics and Chemical Properties of Black Soldier Fly (Hermetia illucens) Larvae as a Potential Protein Source for Poultry Feed

The aim of this study was to investigate and compare the effects of different drying methods on the physical and chemical properties of black soldier fly larvae (BSFL) to determine their potential as an alternative protein source in animal feed. The experimental design was a 2 × 3 factorial arrangement in a completely randomized design (BSFL type × drying method), with five replications. The influence of post-harvest procedures was studied, including the different BSFL types (non-defatted and defatted) and drying methods (parabola dome, hot air oven, and microwave). The results showed that the types of BSFL, drying methods, and their interaction significantly (p < 0.001) influenced the feed's physical properties; these included the brightness of color (L* 29.74-54.07; a* 0.40-5.95; b* 9.04-25.57), medium bulk density (381.54-494.58 g/L), free flow with an angle of repose (41.30-45.40°), and small particle size. They significantly (p < 0.001) influenced the nutritive value of BSFL, which contained 42-59% crude protein, 7-14% crude fiber, 9-30% ether extract, and 5035-5861 kcal/kg of energy. Overall, both BSFL types and all the drying methods resulted in a slight variation in the proximate composition. However, a microwave and a hot-air oven were considered the most suitable methods for producing BSFL powder because of the high levels of nutrients retained and the improved physical parameters when compared to a parabola dome. This characterization of the physical and chemical composition of BSFL represents a preliminary methodology that could be used to initially preprocess larvae for use as an alternative protein source in animal feed and for other applications.

Xylella fastidiosa inoculation behaviors (EPG X wave) are performed differently by blue-green sharpshooters based on infection status of prior probing host

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.

Indoor resting behavior of Aedes aegypti (Diptera: Culicidae) in northeastern Thailand

BACKGROUND

Aedes aegypti is a vector of several arboviruses, notably dengue virus (DENV), which causes dengue fever and is often found resting indoors. Culex spp. are largely nuisance mosquitoes but can include species that are vectors of zoonotic pathogens. Vector control is currently the main method to control dengue outbreaks. Indoor residual spraying can be part of an effective vector control strategy but requires an understanding of the resting behavior. Here we focus on the indoor-resting behavior of Ae. aegypti and Culex spp. in northeastern Thailand.

METHODS

Mosquitoes were collected in 240 houses in rural and urban settings from May to August 2019 at two collection times (morning/afternoon), in four room types (bedroom, bathroom, living room and kitchen) in each house and at three wall heights (< 0.75 m, 0.75-1.5 m, > 1.5 m) using a battery-driven aspirator and sticky traps. Household characteristics were ascertained. Mosquitoes were identified as Ae. aegypti, Aedes albopictus and Culex spp. Dengue virus was detected in Ae. aegypti. Association analyses between urban/rural and within-house location (wall height, room), household variables, geckos and mosquito abundance were performed.

RESULTS

A total of 2874 mosquitoes were collected using aspirators and 1830 using sticky traps. Aedes aegypti and Culex spp. accounted for 44.78% and 53.17% of the specimens, respectively. Only 2.05% were Ae. albopictus. Aedes aegypti and Culex spp. rested most abundantly at intermediate and low heights in bedrooms or bathrooms (96.6% and 85.2% for each taxon of the total, respectively). Clothes hanging at intermediate heights were associated with higher mean numbers of Ae. aegypti in rural settings (0.81 [SEM: 0.08] vs. low: 0.61 [0.08] and high: 0.32 [0.09]). Use of larval control was associated with lower numbers of Ae. aegypti (yes: 0.61 [0.08]; no: 0.70 [0.07]). All DENV-positive Ae. aegypti (1.7%, 5 of 422) were collected in the rural areas and included specimens with single, double and even triple serotype infections.

CONCLUSIONS

Knowledge of the indoor resting behavior of adult mosquitoes and associated environmental factors can guide the choice of the most appropriate and effective vector control method. Our work suggests that vector control using targeted indoor residual spraying and/or potentially spatial repellents focusing on walls at heights lower than 1.5 m in bedrooms and bathrooms could be part of an integrated effective strategy for dengue vector control.

Selective Elimination of Wolbachia from the Leafhopper Yamatotettix flavovittatus Matsumura

Wolbachia infections affect the reproductive system and various biological traits of the host insect. There is a high frequency of Wolbachia infection in the leafhopper Yamatotettix flavovittatus Matsumura. To investigate the potential roles of Wolbachia in the host, it is important to generate a non-Wolbachia-infected line. The efficacy of antibiotics in eliminating Wolbachia from Y. flavovittatus remains unknown. This leafhopper harbors the mutualistic bacterium Candidatus Sulcia muelleri, which has an important function in the biological traits. The presence of Ca. S. muelleri raises a major concern regarding the use of antibiotics. We selectively eliminated Wolbachia, considering the influence of antibiotics on leafhopper survival and Ca. S. muelleri prevalence. The effect of artificial diets containing different doses of tetracycline and rifampicin on survival was optimized; high dose (0.5 mg/ml) of antibiotics induces a high mortality. A concentration of 0.2 mg/ml was chosen for the subsequent experiments. Antibiotic treatments significantly reduced the Wolbachia infection, and the Wolbachia density in the treated leafhoppers sharply declined. Wolbachia recurred in tetracycline-treated offspring, regardless of antibiotic exposure. However, Wolbachia is unable to be transmitted and restored in rifampicin-treated offspring. The dose and treatment duration had no significant effect on the infection and density of Ca. S. muelleri in the antibiotic-treated offspring. In conclusion, Wolbachia in Y. flavovittatus was stably eliminated using rifampicin, and the Wolbachia-free line was generated at least two generations after treatment. This report provides additional experimental procedures for removing Wolbachia from insects, particularly in host species with the coexistence of Ca. S. muelleri.

Bacterial challenge-associated metabolic phenotypes in Hermetia illucens defining nutritional and functional benefits

Black soldier fly (BSF, Hermetia illucens) is popular for its applications in animal feed, waste management and antimicrobial peptide source. The major advantages of BSF larva include their robust immune system and high nutritional content that can be further developed into more potential agricultural and medical applications. Several strategies are now being developed to exploit their fullest capabilities and one of these is the immunity modulation using bacterial challenges. The mechanism underlying metabolic responses of BSF to different bacteria has, however, remained unclear. In the current study, entometabolomics was employed to investigate the metabolic phenoconversion in response to either Escherichia coli, Staphylococcus aureus, or combined challenges in BSF larva. We have, thus far, characterised 37 metabolites in BSF larva challenged with different bacteria with the major biochemical groups consisting of amino acids, organic acids, and sugars. The distinct defense mechanism-specific metabolic phenotypes were clearly observed. The combined challenge contributed to the most significant metabolic phenoconversion in BSF larva with the dominant metabolic phenotypes induced by S. aureus. Our study suggested that the accumulation of energy-related metabolites provided by amino acid catabolism is the principal metabolic pathway regulating the defense mechanism. Therefore, combined challenge is strongly recommended for raising BSF immunity as it remarkably triggered amino acid metabolisms including arginine and proline metabolism and alanine, aspartate and glutamate metabolism along with purine metabolism and pyruvate metabolism that potentially result in the production of various nutritional and functional metabolites.

Population Dynamics of Wolbachia in the Leafhopper Vector Yamatotettix flavovittatus (Hemiptera: Cicadellidae)

Wolbachia (Rickettsiales: Alphaproteobacteria) infections induce abnormalities in the reproductive system and affect various biological traits of the host insects. The density of Wolbachia is one of the major parameters that influence induced phenotypes and interactions with the hosts. Wolbachia occurs naturally in populations of the leafhopper Yamatotettix flavovittatus Matsumura (Hemiptera: Cicadellidae), which transmits phytoplasma that cause white leaf disease in sugarcane. However, the quantity and dynamics of Wolbachia in this leafhopper are not well understood. In the current study, we estimated the number of Wolbachia by absolute quantification of the copy number of wsp, which encodes the outer surface protein, using real-time quantitative polymerase chain reaction (PCR). This investigation was performed using natural populations and laboratory colonies from three lineages of leafhoppers (designated as UD, KK, and SK). There was no significant difference in the number of wsp copies in most of field-collected adults. During the immature developmental stages, there were differences in the dynamics of Wolbachia infection between the UD lineage and the other two lineages. However, the number of wsp copies increased in the early instar and plateaued in the later nymphal instars. Sex had no influence on the number of Wolbachia within the same lineages. The number of Wolbachia was relatively constant during the adult stage in the UD lineage but fluctuated in the other two lineages. In conclusion, the present data provide a framework for exploring the relationship between Wolbachia and the leafhopper and could facilitate future research into management strategies using Wolbachia.

Alteration in the Stylet Probing Behavior and Host Preference of the Vector Matsumuratettix hiroglyphicus (Hemiptera: Cicadellidae) After Infection with Sugarcane White Leaf Phytoplasma

The leafhopper (Matsumuratettix hiroglyphicus (Matsumura) (Hemiptera: Cicadellidae)) is a crucial insect vector of the phytoplasma associated with sugarcane white leaf (SCWL) disease. The aim of this study was to compare the stylet probing behaviors of M. hiroglyphicus on healthy sugarcane plants, asymptomatic, and symptomatic SCWL-infected sugarcane plants, using DC electropenetrography. We also used host-selection preference (free-choice) assays to identify the preferred types of host plants, and scanning electron microscopy to observe stylet puncture holes and salivary flanges after leafhopper probing. According to a quantitative analysis of M. hiroglyphicus stylet probing, mean durations per insect of both phloem ingestion (waveform D; the phytoplasma-acquisition behavior) and phloem salivation (waveform C; the phytoplasma-inoculation behavior) were significantly longer on both types of infected sugarcane than on healthy plants. These longer overall durations were mainly because the same number of significantly longer-duration C and D events was performed on infected sugarcane compared with healthy plants. On free-choice tested plants, M. hiroglyphicus displayed a significantly greater preference to settle on the infected plants (both types) than the healthy sugarcane. These results provide the first empirical evidence that acquiring the SCWL phytoplasma alters the host selection and stylet probing behaviors of its main vector (M. hiroglyphicus). Our study thus contributes to a better understanding of the interactions between the insect vector and SCWL phytoplasma-infected plants, and will aid in developing novel disease management tactics for sugarcane.

Global population genetic structure and demographic trajectories of the black soldier fly, Hermetia illucens

Background

The black soldier fly (Hermetia illucens) is the most promising insect candidate for nutrient-recycling through bioconversion of organic waste into biomass, thereby improving sustainability of protein supplies for animal feed and facilitating transition to a circular economy. Contrary to conventional livestock, genetic resources of farmed insects remain poorly characterised. We present the first comprehensive population genetic characterisation of H. illucens. Based on 15 novel microsatellite markers, we genotyped and analysed 2862 individuals from 150 wild and captive populations originating from 57 countries on seven subcontinents.

Results

We identified 16 well-distinguished genetic clusters indicating substantial global population structure. The data revealed genetic hotspots in central South America and successive northwards range expansions within the indigenous ranges of the Americas. Colonisations and naturalisations of largely unique genetic profiles occurred on all non-native continents, either preceded by demographically independent founder events from various single sources or involving admixture scenarios. A decisive primarily admixed Polynesian bridgehead population serially colonised the entire Australasian region and its secondarily admixed descendants successively mediated invasions into Africa and Europe. Conversely, captive populations from several continents traced back to a single North American origin and exhibit considerably reduced genetic diversity, although some farmed strains carry distinct genetic signatures. We highlight genetic footprints characteristic of progressing domestication due to increasing socio-economic importance of H. illucens, and ongoing introgression between domesticated strains globally traded for large-scale farming and wild populations in some regions.

Conclusions

We document the dynamic population genetic history of a cosmopolitan dipteran of South American origin shaped by striking geographic patterns. These reflect both ancient dispersal routes, and stochastic and heterogeneous anthropogenic introductions during the last century leading to pronounced diversification of worldwide structure of H. illucens. Upon the recent advent of its agronomic commercialisation, however, current human-mediated translocations of the black soldier fly largely involve genetically highly uniform domesticated strains, which meanwhile threaten the genetic integrity of differentiated unique local resources through introgression. Our in-depth reconstruction of the contemporary and historical demographic trajectories of H. illucens emphasises benchmarking potential for applied future research on this emerging model of the prospering insect-livestock sector.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01029-w.

Effect of Wolbachia infection states on the life history and reproductive traits of the leafhopper Yamatotettix flavovittatus Matsumura

Wolbachia is a maternally inherited bacterium of insects that can affect host reproduction and fitness. We examined the effect of Wolbachia infection on the life history and reproductive traits of the leafhopper Yamatotettix flavovittatus, which is a vector of the phytoplasma that causes white leaf disease in sugarcane. This investigation was performed using Wolbachia-infected and uninfected leafhopper lineages. Results revealed that Wolbachia infection did not significantly affect the survival of nymphal stages, male longevity, and sex ratio. However, Wolbachia-infected lineages had prolonged immature development periods and female longevity. In intrapopulation crosses, Wolbachia infection had no significant effects on occupation success, number of eggs laid, and female offspring, but the effect on egg-hatching varied. In interpopulation crosses, Wolbachia infection had no significant effect on occupation success and female offspring, but it did affect the number of eggs laid and egg-hatching rates. Assortative pairings regarding infection status resulted in normal egg deposition and hatching, whereas disassortative pairings resulted in lower egg deposition and no hatching. Wolbachia was thus shown to be highly vertically transmitted (>98% of the tested individuals). Our findings provide additional data on the interactions between Wolbachia in insect hosts. This evidence of perfect maternal transmission and strong reproductive incompatibility highlights the importance of further studies on the use of Wolbachia as a biological control agent for the leafhopper vector.

Wolbachia (Rickettsiales: Alphaproteobacteria) Infection in the Leafhopper Vector of Sugarcane White Leaf Disease

Wolbachia is a maternally inherited bacterium ubiquitous in insects that has attracted interest as a prospective insect pest-control agent. Here, we detected and characterized Wolbachia in the leafhoppers Matsumuratettix hiroglyphicus (Matsumura) (Cicadellidae: Hemiptera) and Yamatotettix flavovittatus Matsumura (Cicadellidae: Hemiptera), insect vectors of the phytoplasma that cause white leaf disease in sugarcane. The 16S rRNA and wsp gene markers revealed that Wolbachia was not present in the M. hiroglyphicus but naturally occurs in Y. flavovittatus. Additionally, the infection rates in adult leafhoppers ranged from 0 to 100% depending on geographic location. Moreover, Wolbachia was detected in the eggs and first- to fifth-instar nymphs of Y. flavovittatus. A phylogenic tree of Wolbachia indicated that it resided in the monophyletic supergroup B clade and clustered in the Ori subgroup. Furthermore, fluorescence in situ hybridization revealed that Wolbachia localized to the egg apices, randomly distributed in the egg cytoplasm, and was concentrated in the nymph and adult bacteriomes, as well as occasional detection in the thorax and abdomen. To the best of our knowledge, the present study is the first to demonstrate the prevalence of Wolbachia in the leafhopper Y. flavovittatus. The obtained results would provide useful information for the future development of Wolbachia as a biological control agent for the leafhopper vectors.

Characterization of Direct Current-Electrical Penetration Graph Waveforms and Correlation With the Probing Behavior of Matsumuratettix hiroglyphicus (Hemiptera: Cicadellidae), the Insect Vector of Sugarcane White Leaf Phytoplasma

The leafhopper Matsumuratettix hiroglyphicus (Matsumura) (Hemiptera: Cicadellidae) is an important vector of phytoplasma causing white leaf disease in sugarcane. Thus, the aim of our study was to understand and describe the stylet-probing activities of this vector while feeding on sugarcane plants, by using direct current (DC) electrical penetration graph (EPG) monitoring. The EPG signals were classified into six distinct waveforms, according to amplitude, frequency, voltage level, and electrical origin of the observed traces during stylet penetration into the host plant tissues (probing). These six EPG waveforms of probing behavior comprise no stylet penetration (NP); stylet pathway through epidermis, mesophyll, and parenchymal cells (waveform A); contact at the bundle sheath layer (waveform B); salivation into phloem sieve elements (waveform C); phloem sap ingestion (waveform D); and short ingestion time of xylem sap (waveform E). The above waveform patterns were correlated with histological data of salivary sheath termini in plant tissue generated from insect stylet tips. The key findings of this study were that M. hiroglyphicus ingests the phloem sap at a relatively higher rate and for longer duration from any other cell type, suggesting that M. hiroglyphicus is mainly a phloem-feeder. Quantitative comparison of probing behavior revealed that females typically probe more frequently and longer in the phloem than males. Thus, females may acquire and inoculate greater amounts of phytoplasma than males, enhancing the efficiency of phytoplasma transmission and potentially exacerbating disease spreading. Overall, our study provides basic information on the probing behavior and transmission mechanism of M. hiroglyphicus.

Sugarcane White Leaf Disease Incidences and Population Dynamic of Leafhopper Insect Vectors in Sugarcane Plantations in Northeast Thailand

The work consisted of two experiments, i.e. Experiment 1 was conducted under controlled environments where sugarcane plants were used as hosts. This investigation aimed to monitor the occurrence of the Sugarcane White Leaf disease and the abundance of Leafhopper insect vectors and also the work aimed to provide useful information in understanding some aspects on epidemiology of the Sugarcane White Leaf disease. A Completely Randomized Design with three replications was used to justify growth and development of Leafhopper insects as affected by different temperatures: 20 (T1), 25 (T2), 30 (T3) and 35 degrees C (T4). Experiment 2 was carried out to determine the numbers of Leafhopper insects with the use of light traps in the sugarcane Field 1 (ratoon plants), Field 2 (newly planted), Field 3 (newly planted) and Field 4 (ratoon plants). The results of Experiment 1 showed that growth and development of Leafhopper insects were highly affected by temperatures i.e. the higher the environmental temperature the faster the growth and development of the insects to reach its full adulthood. At 20 degrees C, Leafhopper insects took 12 days to lay eggs whereas at 25 degrees C the insects took only 6 days. Male reached its adulthood approximately 9 days earlier than female when cultured at 25 degrees C and became approximately one week at 30 degrees C or higher. The results of Experiment 2 showed that the majority of Leafhopper insects were found within the months of June and July for both newly planted and ratoon crops. A small amount was found in May and August with an exceptional case of Field 4 where the highest number of Leafhopper insects was found in April followed by June and July. For Sugarcane White Leaf disease, the disease was found in all months of the year except February for Fields 2 and 3. Newly planted sugarcane plants attained much smaller percentages of disease than those of the ratoon plants.

Candidates for symbiotic control of sugarcane white leaf disease

The leafhopper Matsumuratettix hiroglyphicus (Matsumura) is the most important vector of a phytoplasma pathogen causing sugarcane white leaf (SCWL) disease. The purpose of this study was to evaluate candidate bacterial symbionts for possible use as vehicles in the control of the disease. 16S rRNA bacterial genes were amplified from whole bodies of M. hiroglyphicus leafhoppers and analyzed by cloning and sequencing. Two dominant groups were found: one belonged to the Betaproteobacteria that did not closely match any sequences in the database and was named bacterium associated with M. hiroglyphicus (BAMH). Another one found to be abundant in this leafhopper is "Candidatus Sulcia muelleri" in the order Bacteroidetes, which was previously reported in the insect members of the Auchenorrhyncha. Most M. hiroglyphicus leafhoppers carry both BAMH and "Ca. Sulcia muelleri." Fluorescent in situ hybridization showed that BAMH and "Ca. Sulcia muelleri" colocalized in the same bacteriomes. BAMH was present in the midgut and ovaries of the leafhopper and was found in all developmental stages, including eggs, nymphs, and adults. Because BAMH appears to be specific for the SCWL vector, we evaluated it as a candidate for symbiotic control of sugarcane white leaf disease.

Transmission of sugarcane white leaf phytoplasma by Yamatotettix flavovittatus, a new leafhopper vector

Sugarcane white leaf disease is caused by plant pathogenic phytoplasmas that are transmitted to the plant by the leafhopper Matsumuratettix hiroglyphicus (Matsumura). To determine whether there are other insect vectors that transmit this disease pathogen, leafhopper species in sugarcane, Saccharum officinarum L., fields in northeastern Thailand were monitored by using light traps. Sixty-nine leafhopper species from family Cicadellidae were found. Using nested polymerase chain reaction (PCR) with specific primers, a 210-bp amplified DNA fragment corresponding to phytoplasma associated with sugarcane white leaf disease was detected from 12 species of leafhoppers [Balclutha rubrostriata (Melichar), Balclutha sp., Bhatia olivacea (Melichar), Exitianus indicus Distant, Macrosteles striifrons Anufriew, Matsumuratettix hiroglyphicus (Matsumura), Recilia distincta (Motschulsky), Recilia dorsalis (Motschulsky), Recilia sp., Thaia oryzivora Ghauri, Yamatotettix flavovittatus Matsumura, and Xestocephalus sp.]. The percentage of individual infection with phytoplasma varied from 5% in B. olivacea to 35% in Xestocephalus sp. The most abundant leafhopper species, i.e., E. indicus, Y. flavovittatus, and M. hiroglyphicus were used in transmission tests to determine their vector status for the sugarcane white leaf phytoplasma transmission. Infected insects were reared on healthy plants and specific PCR followed by sequencing of the amplicons was used to determine whether the phytoplasma was transmitted to the plants. The results showed that both Y. flavovittatus and M. hiroglyphicus, but not E. indicus, can transmit sugarcane white leaf phytoplasma to healthy sugarcane plants. The transmission efficiency of M. hiroglyphicus (55%) was higher than that of Y. flavovittatus (45%). We conclude that Y. flavovittatus is a newly discovered vector for sugarcane white leaf disease, in addition to M. hiroglyphicus. These two species peak at different times of the year and therefore complement each other in the transmission of the phytoplasma. Because there are no known alternative host plants for the sugarcane white leaf, management of the disease will necessarily require the control of both Y. flavovittatus and M. hiroglyphicus.

Transovarial transmission of sugarcane white leaf phytoplasma in the insect vector Matsumuratettix hiroglyphicus (Matsumura)

White leaf is a serious disease of sugarcane caused by phytoplasma. The disease is transmitted to the plant by the leafhopper Matsumuratettix hiroglyphicus (Matsumura). The reservoir of phytoplasma was suspected to be weeds that grow in sugarcane farming areas because they can be infected with phytoplasma and show symptoms similar to sugarcane white leaf. However in previous work we have demonstrated by RFLP and sequencing that this is not the case. Here we have reared M. hiroglyphicus through two generations by feeding them phytoplasma free sugarcane grown from tissue culture. By nested-PCR followed by sequencing, we demonstrated the presence of the phytoplasma in eggs, nymphs and adults of the first and second generations thereby showing transovarial transmission. We have also shown by in situ PCR that phytoplasmas were widely distributed throughout the body of the insect. RFLP and sequencing showed that the same phytoplasma was present in the vector and in the plant. Together, these data point to the leafhopper M. hiroglyphicus as the reservoir of phytoplasma that cause sugarcane white leaf disease.