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David N. Byrne - One of the best experts on this subject based on the ideXlab platform.
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Wild and Colonized Populations of Bemisia tabaci Display Dramatically Different Patterns of Dispersal Ability.
2015Co-Authors: David N. Byrne, Jesse A Hardin, Department EntomologyAbstract:Introduction: Along with other members of our laboratory, I have been examining various aspects of dispersal and migration by Bemisia tabaci, the Sweet Potato Whitefly, for approximately 15 y. We have determined a number of things including: the fact that B. tabaci engages in behavior that fits historical definitions of migration; how wing loading relates to wingbeat frequency; and descriptions of B. tabaci and Eretmoceru
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have distances traveled by the Sweet Potato Whitefly been underestimated
Vegetable Report, 2008Co-Authors: David N. Byrne, Jesse A HardinAbstract:The importance of the Sweet Potato Whitefly to Arizona vegetable continues to ebb and flow from year to year. Over the last 25 years much of this likely is tied to the invasion by different strains. As we continue to study this insect, an aspect of importance to their management is their ability to disperse. In past studies we have determined how far they are capable of flying in a day’s time, 95% migrate 1.6 miles. We are now investigating their ability to fly multiple days. If they do migrate on more than 1 day, we must readjust our estimates of their influence on surrounding fields. Introduction The Sweet Potato Whitefly, Bemisia tabaci, has been a significant pest of vegetable crops and cotton since populations greatly expanded in the early 1980s. Some attribute this to the extensive use of pyrethroid insecticides. A more likely explanation, however, given our current understanding of the extreme differences in subsets of the Sweet Potato Whitefly species, is that there was an introduction of a new strain, strain A, into our production system. A similar occurrence likely took place in the late 1980s with the arrival of strain B, and now we face the possibility of a reoccurrence with the arrival on nursery stock of a third strain, strain Q. Strain Q has not been reported in the field in Arizona, but has been seen there in Florida. The fact that these invasions are responsible for increased numbers of Sweet Potato whiteflies is likely, but unproven. Regardless of cause, it is undeniable that the Sweet Potato Whitefly is often present in large numbers and needs to be better understood from a pest management perspective. One the most impressive aspects of Sweet Potato Whitefly behavior, a phenomenon that could be of consequence to growers (see below), is the ability of these insects to migrate between crops in southwestern agricultural systems. Past experiments show that Sweet Potato whiteflies are capable of sustained flight in the laboratory for at least 3 hours. This was learned by examining Whitefly flight behavior in a laboratory setting using a vertical chamber (Fig. 1). The operation of the chamber remains simple. The Arizona chamber consists of a large, 18 ft, open-fronted box with a central opening in the roof into which fits a smaller open box containing a sodium vapor light (sky cue). Mounted on the side of the chamber is a blue/green light source that simulates a plant cue. Muslin screens dampen air turbulence. The draft is regulated not by changing the fan speed, but by adjusting the chamber aperture. This is done manually using a handle. The setting of the aperture is constantly adjusted to keep the flying insect 7 inches below the screen of the light box. Digital readings from an anemometer measure wind flow generated by the overhead fan and are recorded by a computer. Vegetable Report (P-152), January 2008 51 These data are an indirect measure of insect rate of ascent. Insects ignoring the plant cue while flying towards the sky cue for an extended period are identified as being migratory. This behavior fits accepted definitions of migratory behavior. These laboratory data concerning sustained flight were corroborated in field studies conducted in Yuma. Sweet Potato whiteflies were marked and their distribution following dispersal across an 8-mile grid was noted. A significant portion of the Whitefly population dispersed farther than 1.6 miles in a 4-hr period. This could easily carry them into a new crop. We did not ask if this insect flew a similar distance the following day. We now find that we may have been underestimating the distances traveled by these whiteflies when migrating. This is because we now have preliminary information indicating these insects fly on more than one day. We are often asked questions such as, “How far away must an unplowed watermelon field be before I do not have to worry about those Whitefly populations affecting my crops? – or – How far is this plant disease going to spread in a season?” Answers that we were comfortable providing in the past may not be correct. We may have to adjust our response based on new results. There is currently disagreement between the relative importance of long-range migration from Mexico and Central America as opposed to local intercrop migration by whiteflies across the growing season as a contributor to Whitefly populations. We currently believe that there are large resident Sweet Potato Whitefly populations in Arizona that simply move into crops as new sites become available. We also believe such long-range flight was not within the capabilities of the Sweet Potato Whitefly. We need better empirical evidence, however. Materials and Methods To determine whether the Sweet Potato Whitefly flies on multiple days we returned to the flight chamber. Whiteflies were reared on cowpeas. Leaf punches with large nymphal populations were taken from leaves and placed in Petri dishes containing agar-filled bottoms. The next day, newly emerged whiteflies were placed individually in similar dishes. The following day, these insects were transferred to small vials and placed in the flight chamber. They were given 3 minutes to fly toward the sky cue. We counted as having flown any insect that initiated any flight, regardless of whether it simply flitted from the vial or flew for as long as 18 minutes. Additional analyses are necessary. The proportion initiating flight, their rate of ascent, and number that continued to fly toward the sky cue were recorded. After being in the chamber, insects were returned to new Petri dishes with new leaves. This process was repeated for up to 10 consecutive days (8 were more usual) or until the individual whiteflies were either lost or died. Results and Discussion To date were have observed a total of 98 individual whiteflies. We did find that certain of these whiteflies flew on multiple days (Fig. 2). This figure indicates that 50% of observed whiteflies flew on Day 1. Of 1 If they continued to fly toward the sky cue and ignored the plant cue, they were identified as being migratory. 2 In the beginning, most insects are lost, squashed, or disappeared into the ethers. As techniques improved, our sample size has increased. Vegetable Report (P-152), January 2008 52 those that flew on Day 1, 47% flew on Day 2. These data are shown to Day 10. Although we present our data on consecutive day flights above, we do not know the importance of multiple day flights toward total lifetime movement by individual insects. What we have not yet determined, for example, is whether or not insects that flew on Day 5 also on Day 2. This information is available, but data have not yet been analyzed. We also have information that shows that some females had flights as many as 10 days following emergence. No male flew after Day 5. We also know on which day whiteflies flew the longest (Fig. 3). The most flights and the longest flights took place on Day 1. This figure is somewhat deceiving since very few whiteflies were available to fly on Day 7; many were lost by that time. On that day there we have information on 15 only insects. Of the seven that flew, one flew for 5 min., 12 sec., greatly biasing the data. Of the 98 insects that we observed, only two engaged in migratory flight, i.e., they flew toward the sky cue for an extended period while ignoring the plant cue. Neither of these flew a second day. From previous studies, we know that it is the migratory individuals that fly between crops. Of the others that flew, even those flying as long as 18 minutes were engaged in foraging flight. This would keep them in the fields where they originated. We are confident we will be able to answer questions about Sweet Potato whiteflies migrate on several days once our data is all collected. This will provide a clearer picture of how whiteflies can travel as adults. We have learned the following in our laboratory studies. • Our longest male flight was 30 min., 38 sec. • Our longest female flight was 17 min., 35 sec. Of those flying for > 100 sec, none flew again • One female flew 5 of 7 days • We have egg deposition data that are yet to be explored • We know how fast they were flying and for how long, so we can estimate distance traveled. These data need to be explored more fully. Our future objectives include adding to our laboratory data set. We also realize that our conclusions on distances traveled will have to be corroborated with field data. Can these insects survive for a second day of a flight having experienced the stress of being airborne under field conditions? What is the effect of wind on movement? We hope to begin these experiments in the field in Yuma next summer.
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Field Evaluation of Eretmocerus eremicus Efficacy in the Control of Sweet Potato Whiteflies Infesting Melons
Vegetable Report, 2002Co-Authors: David E. Bellamy, Mark K Asplen, David N. ByrneAbstract:The effect of three different release rates (1x, 10x, and 20x the recommended rate of 10,000/acre) of Eretmocerus eremicus, a Whitefly parasitoid, on Sweet Potato Whitefly populations in cantaloupe were evaluated against populations in untreated control plots. Parasitoids were released from a point source in the center of each of nine treatment plots. All stages of Whitefly development were monitored within a 10-m annulus surrounding each release point in all 12 plots, as were rates of parasitism. This occurred over a 52-d period from July 21 through September 11, 2001. The rates of Sweet Potato Whitefly population increase during this time were equivalent and independent of the parasitoid release rate. Whitefly densities were not controlled in any of our treatment plots, nor in the controls. Moreover, rates of parasitism did not increase with time in any of the treatment plots and did not differ among the three release rates (22.0 ± 16.2%). Hence, Eretmocerus eremicus, by itself, is not efficient as a means to control Whitefly populations in melon crops in the Southwest US. The ineffectiveness of E. eremicus to control Whitefly populations in the field may be due to its propensity to dispersal at low host densities.
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migration and dispersal by the Sweet Potato Whitefly bemisia tabaci
Agricultural and Forest Meteorology, 1999Co-Authors: David N. ByrneAbstract:Abstract Research on short-range dispersal (less than 10 km) by supposedly weakly flying insects, e.g., whiteflies, has not enjoyed the attention paid to dispersal by strong flying insects that are capable of migrating more than 100 km, such as some leafhoppers. Possible exceptions are studies concerning dispersal by the Sweet Potato Whitefly, Bemisia tabaci . We wanted to determine to what extent Whitefly flight is truly weak and if it meets some of the criteria historically used to define migration. In a flight chamber the majority of whiteflies landed quickly. A portion (6%) flew for more than 15 min (some more than 2 h). In doing so whiteflies ignored vegetative cues and focused on artificial skylight. This was against a downwardly directed airstream exceeding 4.0 cm/s. Attempts to associate wing morphological characteristics with their flight were mostly successful. The shapes of the wings of whiteflies that flew for some time in the chamber, or for some distance in the field, were different than those that did not. In the field B. tabaci was found dispersing more than 5 km. In these experiments whiteflies in a cantaloupe field were marked with fluorescent dust. Large portions of the marked population landed in close proximity to the field and another large group was trapped at 2.2 km. We hypothesized that this conformed to flight behavior observed in the laboratory, i.e., individuals captured near the field quickly responded to vegetative cues and landed, while others dispersed down range, initially ignoring these plant cues. This behavior was thought to be persistent. Additionally, flight in the field was not entirely wind-directed. Whiteflies were sometimes captured in areas away from prevailing winds. These are indicative of strong flight and migration. We found, however, that whiteflies did not possess all the characteristics commonly associated with stronger flyers. Whiteflies do not increase wingbeat frequency to compensate for high wing loading. Whiteflies do not possess an oogenesis-flight syndrome. In spite of these findings, Whitefly flight cannot be characterized as weak. Whiteflies flew in a flight chamber against a strong airstream. They also dispersed in field experiments for a considerable distance. There is also information that whiteflies have a migratory form, in the manner of some strong flying insects. Whitefly flight seems to meet many criteria associated with migration in insects. As a final note, although most Whitefly flight occurs over short distances, it is no less important biologically and cannot be ignored when developing pest management programs.
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does dispersal affect the reproductive physiology of the Sweet Potato Whitefly bemisia tabaci
Physiological Entomology, 1999Co-Authors: Klaas H Veenstra, David N. ByrneAbstract:.The reproductive physiology of Sweet Potato whiteflies, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was examined after their dispersal from cotton fields. Of particular interest was the synthesis of vitellogenins and the production of mature eggs. Whiteflies that dispersed out of fields, and were flying at ≈ 0.1 m above the soil surface, exhibited a reproductive physiology that was not significantly different from whiteflies that remained in cotton fields. However, B. tabaci caught at 2.1 m above the ground matured eggs at a significantly lower rate. It appears these latter whiteflies exhibit a physiology that indicates a reallocation of nutrient and energy resources in support of movement.
Garry N Hannan - One of the best experts on this subject based on the ideXlab platform.
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the x ray structure of a hemipteran ecdysone receptor ligand binding domain comparison with a lepidopteran ecdysone receptor ligand binding domain and implications for insecticide design
Journal of Biological Chemistry, 2005Co-Authors: Jennifer A Carmichael, Lloyd D Graham, Michael C Lawrence, Patricia A Pilling, Leonie Noyce, George O Lovrecz, David A Winkler, Anna Pawlakskrzecz, Ruth E Eaton, Garry N HannanAbstract:Abstract The ecdysone receptor is a hormone-dependent transcription factor that plays a central role in regulating the expression of vast networks of genes during development and reproduction in the phylum Arthropoda. The functional receptor is a heterodimer of the two nuclear receptor proteins ecdysone receptor (EcR) and ultraspiracle protein. The receptor is the target of the environmentally friendly bisacylhydrazine insecticides, which are effective against Lepidoptera but not against Hemiptera or several other insect orders. Here we present evidence indicating that much of the selectivity of the bisacylhydrazine insecticides can be studied at the level of their binding to purified ecdysone receptor ligand-binding domain (LBD) heterodimers. We report the crystal structure of the ecdysone receptor LBD heterodimer of the hemipteran Bemisia tabaci (Bt, Sweet Potato Whitefly) in complex with the ecdysone analogue ponasterone A. Although comparison with the corresponding known LBD structure from the lepidopteran Heliothis virescens (Hv) ecdysone receptor revealed the overall mode of ponasterone A binding to be very similar in the two cases, we observed that the BtEcR ecdysteroid-binding pocket is structured differently to that of HvEcR in those parts that are not in contact with ponasterone A. We suggest that these differences in the ligand-binding pocket may provide a molecular basis for the taxonomic order selectivity of bisacylhydrazine insecticides.
Murad Ghanim - One of the best experts on this subject based on the ideXlab platform.
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the presence of rickettsia is associated with increased susceptibility of bemisia tabaci homoptera aleyrodidae to insecticides
Pest Management Science, 2008Co-Authors: Svetlana Kontsedalov, Elad Chiel, Einat Zchorifein, Yuval Gottlieb, Moshe Inbar, Murad GhanimAbstract:BACKGROUND: The presence of certain symbiotic microorganisms may be associated with insecticide resistance in insects. The authors compared the susceptibility of two isofemale lines, Rickettsia-plus and Rickettsia-free, of the Sweet Potato Whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) to major insecticides from different chemical groups, including imidacloprid, acetamiprid, thiamethoxam, pyriproxyfen, spiromesifen and diafenthiuron. RESULTS: While the Rickettsia-plus and Rickettsia-free lines showed no differences in their susceptibility to imidacloprid and diafenthiuron, higher susceptibility of the Rickettsia-plus line to acetamiprid, thiamethoxam, spiromesifen and especially pyriproxyfen was observed. LC90 values indicated that the Rickettsia-free line was 15-fold more resistant to pyriproxyfen than the Rickettsia-plus line. CONCLUSION: Findings indicate that the infection status of B. tabaci populations by Rickettsia is an important consideration that should be taken into account when performing resistance monitoring studies, and may help in understanding the dynamics of B. tabaci resistance, symbiont-pest associations in agricultural systems and the biological impact of Rickettsia on Whitefly biology. 2008 Society of Chemical Industry
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Inherited intracellular ecosystem: symbiotic bacteria share bacteriocytes in whiteflies.
FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 2008Co-Authors: Yuval Gottlieb, Murad Ghanim, Gwenaelle Gueguen, Svetlana Kontsedalov, Fabrice Vavre, Frédéric Fleury, Einat Zchori-feinAbstract:Symbiotic relationships with bacteria are common within the Arthropoda, with interactions that substantially influence the biology of both partners. The symbionts' spatial distribution is essential for understanding key aspects of this relationship, such as bacterial transmission, phenotype, and dynamics. In this study, fluorescence in situ hybridization was used to localize five secondary symbionts from various populations and biotypes of the Sweet Potato Whitefly Bemisia tabaci: Hamiltonella, Arsenophonus, Cardinium, Wolbachia, and Rickettsia. All five symbionts were found to be located with the primary symbiont Portiera inside the bacteriocytes--cells specifically modified to house bacteria--but within these cells, they occupied various niches. The intrabacteriocyte distribution pattern of Rickettsia differed from what has been described previously. Cardinium and Wolbachia were found in other host tissues as well. Because all symbionts share the same cell, bacteriocytes in B. tabaci represent a unique intracellular ecosystem. This phenomenon may be a result of the direct enclosure of the bacteriocyte in the egg during oogenesis, providing a useful mechanism for efficient vertical transmission by "hitching a ride" with Portiera. On the other hand, cohabitation in the same cell provides ample opportunities for interactions among symbionts that can either facilitate (cooperation) or limit (warfare) symbiotic existence.
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biotype dependent secondary symbiont communities in sympatric populations of bemisia tabaci
Bulletin of Entomological Research, 2007Co-Authors: Elad Chiel, Netta Mozesdaube, Einat Zchorifein, Nurit Katzir, Yuval Gottlieb, Moshe Inbar, Murad GhanimAbstract:The Sweet Potato Whitefly, Bemisia tabaci, harbors Portiera aleyrodidarum , an obligatory symbiotic bacterium, as well as several secondary symbionts including Rickettsia , Hamiltonella , Wolbachia, Arsenophonus , Cardinium and Fritschea , the function of which is unknown. Bemisia tabaci is a species complex composed of numerous biotypes, which may differ from each other both genetically and biologically. Only the B and Q biotypes have been reported from Israel. Secondary symbiont infection frequencies of Israeli laboratory and field populations of B. tabaci from various host plants were determined by PCR, in order to test for correlation between bacterial composition to biotype and host plant. Hamiltonella was detected only in populations of the B biotype, while Wolbachia and Arsenophonus were found only in the Q biotype (33% and 87% infection, respectively). Rickettsia was abundant in both biotypes. Cardinium and Fritschea were not found in any of the populations. No differences in secondary symbionts were found among host plants within the B biotype; but within the Q biotype, all whiteflies collected from sage harboured both Rickettsia and Arsenophonus , an infection frequency which was significantly higher than those found in association with all other host plants. The association found between Whitefly biotypes and secondary symbionts suggests a possible contribution of these bacteria to host characteristics such as insecticide resistance, host range, virus transmission and speciation.
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identification and localization of a rickettsia sp in bemisia tabaci homoptera aleyrodidae
Applied and Environmental Microbiology, 2006Co-Authors: Yuval Gottlieb, Elad Chiel, Dan Gerling, Shimon Steinberg, Murad Ghanim, Vitaly Portnoy, Galil Tzuri, Rami A Horowitz, Eduard Belausov, Netta MozesdaubeAbstract:Whiteflies (Homoptera: Aleyrodidae) are sap-sucking insects that harbor “Candidatus Portiera aleyrodidarum,” an obligatory symbiotic bacterium which is housed in a special organ called the bacteriome. These insects are also home for a diverse facultative microbial community which may include Hamiltonella, Arsenophonus, Fritchea, Wolbachia, and Cardinium spp. In this study, the bacteria associated with a B biotype of the Sweet Potato Whitefly Bemisia tabaci were characterized using molecular fingerprinting techniques, and a Rickettsia sp. was detected for the first time in this insect family. Rickettsia sp. distribution, transmission and localization were studied using PCR and fluorescence in situ hybridizations (FISH). Rickettsia was found in all 20 Israeli B. tabaci populations screened but not in all individuals within each population. A FISH analysis of B. tabaci eggs, nymphs, and adults revealed a unique concentration of Rickettsia around the gut and follicle cells, as well as a random distribution in the hemolymph. We postulate that the Rickettsia enters the oocyte together with the bacteriocytes, leaves these symbiont-housing cells when the egg is laid, multiplies and spreads throughout the egg during embryogenesis and, subsequently, disperses throughout the body of the hatching nymph, excluding the bacteriomes. Although the role Rickettsia plays in the biology of the Whitefly is currently unknown, the vertical transmission on the one hand and the partial within-population infection on the other suggest a phenotype that is advantageous under certain conditions but may be deleterious enough to prevent fixation under others.
Jennifer A Carmichael - One of the best experts on this subject based on the ideXlab platform.
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the x ray structure of a hemipteran ecdysone receptor ligand binding domain comparison with a lepidopteran ecdysone receptor ligand binding domain and implications for insecticide design
Journal of Biological Chemistry, 2005Co-Authors: Jennifer A Carmichael, Lloyd D Graham, Michael C Lawrence, Patricia A Pilling, Leonie Noyce, George O Lovrecz, David A Winkler, Anna Pawlakskrzecz, Ruth E Eaton, Garry N HannanAbstract:Abstract The ecdysone receptor is a hormone-dependent transcription factor that plays a central role in regulating the expression of vast networks of genes during development and reproduction in the phylum Arthropoda. The functional receptor is a heterodimer of the two nuclear receptor proteins ecdysone receptor (EcR) and ultraspiracle protein. The receptor is the target of the environmentally friendly bisacylhydrazine insecticides, which are effective against Lepidoptera but not against Hemiptera or several other insect orders. Here we present evidence indicating that much of the selectivity of the bisacylhydrazine insecticides can be studied at the level of their binding to purified ecdysone receptor ligand-binding domain (LBD) heterodimers. We report the crystal structure of the ecdysone receptor LBD heterodimer of the hemipteran Bemisia tabaci (Bt, Sweet Potato Whitefly) in complex with the ecdysone analogue ponasterone A. Although comparison with the corresponding known LBD structure from the lepidopteran Heliothis virescens (Hv) ecdysone receptor revealed the overall mode of ponasterone A binding to be very similar in the two cases, we observed that the BtEcR ecdysteroid-binding pocket is structured differently to that of HvEcR in those parts that are not in contact with ponasterone A. We suggest that these differences in the ligand-binding pocket may provide a molecular basis for the taxonomic order selectivity of bisacylhydrazine insecticides.
Dale B. Gelman - One of the best experts on this subject based on the ideXlab platform.
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The broadly insecticidal Photorhabdus luminescens toxin complex a (Tca): Activity against the Colorado Potato beetle, Leptinotarsa decemlineata, and Sweet Potato Whitefly, Bemisia tabaci
2016Co-Authors: Michael B. Blackburn, John M. Domek, Dale B. GelmanAbstract:toxin complex a (Tca): Activity against the Colorado Potato beetle, Leptinotarsa decemlineata, and Sweet Potato Whitefly, Bemisia tabac
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insecticidal activity of some reducing sugars against the Sweet Potato Whitefly bemisia tabaci biotype b
Journal of Insect Science, 2010Co-Authors: Dale B. Gelman, Michael E Salvucci, Yan P Chen, Michael B. BlackburnAbstract:The effects of 16 sugars (arabinose, cellobiose, fructose, galactose, gentiobiose, glucose, inositol, lactose, maltose, mannitol (a sugar alcohol), mannose, melibiose, ribose, sorbitol, trehalose, and xylose) on Sweet Potato Whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) survival were determined using in vitro bioassays. Of these sugars, arabinose, mannose, ribose, and xylose were strongly inhibitory to both nymphal and adult survival. When 10% mannose was added to the nymphal diet, 10.5%, 1.0%, and 0% developed to the 2nd, 3rd, and 4th instars, respectively. When 10% arabinose was added, 10.8% and 0% of the nymphs molted to the 2nd and 3rd instars, respectively. Addition of 10% xylose or ribose completely terminated B. tabaci development, preventing the molt to the 2nd instar. With decreasing sugar concentrations the inhibitory effect was significantly reduced. In tests using adults, arabinose, galactose, inositol, lactose, maltose, mannitol, mannose, melibiose, ribose, sorbitol, trehalose, and xylose significantly reduced mean day survival. Mortality rates were highest when arabinose, mannitol, mannose, ribose, or xylose was added to the diet. Mean day survival was less than 2 days when adults were fed on diet containing 10% of any one of these five sugars. When lower concentrations of sugars were used there was a decrease in mortality. Mode of action studies revealed that toxicity was not due to the inhibition of alpha glucosidase (converts sucrose to glucose and fructose) and/or trehalulose synthase (converts sucrose to trehalulose) activity. The result of agarose gel electrophoresis of RT-PCR products of bacterial endosymbionts amplified from RNA isolated from whiteflies fed with 10% arabinose, mannose, or xylose indicated that the concentration of endosymbionts in mycetomes was not affected by the toxic sugars. Experiments in which B. tabaci were fed on diets that contained radio-labeled sucrose, methionine or inulin and one or none (control) of the highly toxic sugars showed that radioactivity (expressed in DPM) in the body, in excreted honeydew and/or carbon dioxide, was significantly reduced as compared to controls. Thus, it appears that the ability of insecticidal sugars to act as antifeedants is responsible for their toxicity to B. tabaci.
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the broadly insecticidal photorhabdus luminescens toxin complex a tca activity against the colorado Potato beetle leptinotarsa decemlineata and Sweet Potato Whitefly bemisia tabaci
Journal of Insect Science, 2005Co-Authors: Michael B. Blackburn, John M. Domek, Dale B. GelmanAbstract:Toxin complex a (Tca), a high molecular weight insecticidal protein complex produced by the entomopathogenic bacterium Photorhabdus luminescens, has been found to be orally toxic to both the Colorado Potato beetle, Leptinotarsa decemlineata, and the Sweet Potato Whitefly, Bemisia tabaci biotype B. The 48 hour LC50 for Tca against neonate L. decemlineata was found to be 2.7 ppm, and the growth of 2nd instar L. decemlineata exposed to Tca for 72 hours was almost entirely inhibited at concentrations above 0.5 ppm. B. tabaci was highly susceptible to Tca as well; newly emerged nymphs that were artificially fed Tca developed poorly, or not at all. Tca concentrations between 0.1 and 0.2 ppm reduced the number of nymphs reaching the second instar by 50%. In addition, a preparation of Tca missing two prominent subunits, TcaAii and TcaAiii, was found to be at least as toxic to L. decemlineata and B. tabaci as Tca itself, indicating that the activity of Tca is not dependant on the presence of these subunits at the time of ingestion.
