Host plant pubescence: effect on silverleaf whitefly, Bemisia argentifolii, fourth instar and pharate adult dimensions and ecdysteroid titer fluctuations.
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The ability to generate physiologically synchronous groups of insects is vital to the performance of investigations designed to test insect responses to intrinsic and extrinsic stimuli. During a given instar, the silverleaf whitefly, Bemisia argentifolii, increase in depth but not in length or width. A staging system to identify physiologically synchronous 4th instar and pharate adult silverleaf whiteflies based on increasing body depth and the development of the adult eye has been described previously. This study determined the effect of host plant identity on ecdysteroid fluctuations during the 4th instar and pharate adult stages, and on the depth, length and width dimensions of 4th instar/pharate adult whiteflies. When grown on the pubescent-leafed green bean, tomato and poinsettia plants, these stages were significantly shorter and narrower, but attained greater depth than when grown on the glabrous-leafed cotton, collard and sweet potato plants. Thus, leaf pubescence is associated with reduced length and width dimensions, but increased depth dimensions in 4(th) instars and pharate adults. For all host plants, nymphal ecdysteroid titers peaked just prior to the initiation of adult development. However, when reared on pubescent-leafed plants, the initiation of adult development typically occurred in nymphs that had attained a depth of 0.2 to 0.25 mm (Stage 3 - 4). When reared on glabrous-leafed plants, the initiation of adult development typically occurred earlier, in nymphs that had attained a depth of only 0.15-0.18 mm (Stage 2 Old - early 3). Therefore, based on ecdysteroid concentration, it appears that Stage-2, -3 and -4/5 nymphs reared on pubescent-leafed plants are physiologically equivalent to Stage-1, -2 Young and -2 Old/3, respectively, nymphs reared on glabrous-leafed plants. The host plant affected the width but not the height of the nymphal-adult premolt ecdysteroid peak. However, leaf pubescence was not the determining factor. Thus, host plant identity affects physiological events as well as structural characteristics during whitefly nymphal and adult development. (+info)
Neotenic formation in laboratory colonies of the termite Coptotermes gestroi after orphaning.
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The termite Coptotermes gestroi (Wasmann 1896) (Rhinotermitidae: Coptotermitinae) is an exotic species in Brazil and information concerning its reproductive developmental biology is scarce. We induced the formation of neotenics in laboratory colonies through orphaning experiments. Orphaning experiments were conducted in three-year old colonies of C. gestroi kept under laboratory conditions. After three months, eight nymphoid neotenics were observed in one colony after queen removal. Histological analysis showed that these neotenics were non-functional. The results suggest that these individuals may have arisen from the first nymphal instar (N1) or from an early N1 instar after one or two larval moults. Neotenics also were recorded on two incipient colonies of C. gestroi that lost the queen naturally. (+info)
Effect of different photoperiods on the growth, infectivity and colonization of Trinidadian strains of Paecilomyces fumosoroseus on the greenhouse whitefly, Trialeurodes vaporariorum, using a glass slide bioassay.
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Growth, infectivity and colonization rates for blastospores and conidia of Trinidadian strains T, T10, and T11 of Paecilomyces fumosoroseus (Wize) Brown and Smith were assessed for activity against late fourth-instar nymphs of Trialeurodes vaporariorum (Westwood) (Homoptera:Aleyrodidae) under two different photoperiods (24 and 16 hour photophase). A glass-slide bioassay and a fungal development index, modified for both blastospores and conidia, were used to compare the development rates of the fungal strains on the insect hosts. Fewer adult whiteflies emerged from nymphs treated with blastospores and reared under a 16:8 hour light:dark photoperiod than a 24:0 hour photoperiod. Eclosion times of whitefly adults that emerged from nymphs treated with the different strains of conidia were similar over the 8 day experimental period at both light regimes. The percent eclosion of adult whiteflies seems to be directly correlated with the speed of infection of the blastospore or conidial treatment and the photoperiod regime. The longer photophase had a significant positive effect on development index for blastospores; however, a lesser effect was observed for the conidia at either light regime. Blastospore strain T11 offered the most potential of the three Trinidadian strains against T. vaporariorum fourth-instar nymphs, especially under constant light. The glass-slide bioassay was successfully used to compare both blastospores and conidia of P. fumosoroseus. It can be used to determine the pathogenicity and the efficacy of various fungal preparations against aleyrodid pests. (+info)
Biological effect of 1-dodecanol in teneral and post-teneral Rhodnius prolixus and Triatoma infestans (Hemiptera: Reduviidae).
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Topical application of 1-dodecanol was significantly more toxic against teneral first nymphs (1-3 h old) than post-teneral first nymphs (24 h old). The lethal dose ratios were 711,500 for Rhodnius prolixus and 3613 for Triatoma infestans. No significative difference between LD50 was found when 1-dodecanol was injected in recently hatched adult R. prolixus (1-4 h old) nor in older adults (24 h old). These values were similar to those calculated for deltamethrin (an effective triatomicide), showing that 1-dodecanol had no insecticidal properties when it was applied by injection. Topical application of high dose of 1-dodecanol (1 microg/i) on teneral first nymphs of R. prolixus, produced an interruption of the darkening process of the cuticle, and probably in the development of its physiological properties. (+info)
Juvenile immune system activation induces a costly upregulation of adult immunity in field crickets Gryllus campestris.
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Inducible immune defence may allow organisms a state-dependent upregulation of costly immunity in order to minimize the risk of anticipated future parasitism. The basic costs of elevated immune activity might involve a reduction in other fitness-related traits as well as an increased risk of immunopathology. In male field crickets Gryllus campestris we experimentally investigated the condition-dependent effects of immune system activation in nymphs on immunity and physiological condition during adulthood. Following a nymphal injection of bacterial lipopolysaccharides, adult males showed significantly elevated levels of two major immune parameters, i.e. haemolymph antibacterial activity and the concentration of prophenoloxidase (proPO). By contrast, the active enzyme, phenoloxidase (PO), did not increase, suggesting a strategic long-term upregulation of the inactive proenzyme proPO only. This may help avoid the cytotoxic effects associated with high standing levels of the active enzyme. The nymphal immune insult further caused a reduction in adult haemolymph protein load, suggesting a long-term decline in overall metabolic condition. Nymphal food availability positively affected adult lysozyme activity, while PO and proPO concentrations were not affected. Our data thus suggest the long-term upregulation of immunity in response to antigenic cues as an adaptive, yet costly, invertebrate strategy to improve resistance to future parasitism. (+info)
Role of Borrelia burgdorferi linear plasmid 25 in infection of Ixodes scapularis ticks.
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The tick-borne bacterium Borrelia burgdorferi has over 20 different circular and linear plasmids. Some B. burgdorferi plasmids are readily lost during in vitro culture or genetic manipulation. Linear plasmid 25, which is often lost in laboratory strains, is required for the infection of mice. Strains missing linear plasmid 25 (lp25(-)) are able to infect mice if the BBE22 gene on lp25 is provided on a shuttle vector. In this study, we examined the role of lp25 and BBE22 in tick infections. We tested the hypothesis that complementation with BBE22 in spirochetes lacking lp25 would restore the ability of spirochetes to infect ticks. A natural tick infection cycle was performed by feeding larvae on mice injected with the parental, lp25(-), or lp25(-) BBE22-complemented spirochete strains. In addition, larvae and nymphs were artificially infected with different strains to study tick infections independent of mouse infections. B. burgdorferi missing lp25 was significantly impaired in its ability to infect larval and nymphal ticks. When an lp25(-) strain was complemented with BBE22, the ability to infect ticks was partially restored. Complementation with BBE22 allowed spirochetes lacking lp25 to establish short-term infections in ticks, but in most cases the infection prevalence was lower than that of the wild-type strain. In addition, the number of infected ticks decreased over time, suggesting that another gene(s) on lp25 is required for long-term persistence in ticks and completion of a natural infection cycle. (+info)
Effect of sub-lethal concentrations of permethrin on ovary activation in the predator Supputius cincticeps (Heteroptera: Pentatomidae).
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Insecticides may cause mortality and deleterious effects on predatory stinkbugs. For this reason, the effect of five concentrations of permethrin applied on third instar nymphs of Supputius cincticeps (Stal) (Heteroptera: Pentatomidae) was investigated on ovary activation in this predator. The nymphs received topical application of permethrin in the following concentrations (mg a.i./ml): 10(-7), 10(-6), 10(-5), 10(-4), and 10(-3). Ovary lengths and oocyte numbers were quantified following first egg mass. Ovary length of S. cincticeps varied from 5.7 mm with 10(-4) mg a.i./ml, to 6.4 mm with 10(-7) mg a.i./ml, with similar values for the other permethrin concentrations and for the control. The number of oocytes per female varied from 13.5 with 10(-3) mg a.i./ml, to 29.2 for the control, with significant differences. The number of oocytes per female of nymphs exposed to a permethrin concentration of 10(-5) mg a.i./ml was similar to that of the control. However, the lower number of oocytes per female from nymphs exposed to other concentrations of permethrin suggests that this insecticide may affect the reproductive capacity of this predator. The results obtained are discussed in relation to tolerance of Heteroptera predators to insecticides and possible hormesis occurrence. (+info)
Triatoma rubrovaria (Blanchard, 1843) (Hemiptera-Reduviidae-Triatominae) IV: bionomic aspects on the vector capacity of nymphs.
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Triatoma rubrovaria has become the most frequently captured triatomine species since the control of T. infestans in the state of Rio Grande do Sul (RS), Brazil. The aim of this study was to evaluate aspects of the vectorial competence of T. rubrovaria using nymphs raised in laboratory under environmental conditions of temperature and humidity and fed on mice. The average developmental period of T. rubrovaria was 180.1 days. The percentage of defecation shortly after feeding was still higher than previous studies in which samples of T. rubrovaria subjected to a slight starvation period before the blood meal were used. The obtained results support former indication that T. rubrovaria presents bionomic characteristics propitious to be a good vector of Trypanosoma cruzi to man. Therefore its domiciliary invasion process must be continuously monitored. (+info)