Construction of Synthetic Genes for Analogs of Spider Silk Spidroin 1 and Their Expression in Tobacco Plants

To obtain transgenic tobacco plants expressing recombinant analogs of spider dragline silk spidroin 1, artificial 1f5 and 1f9 coding for spidroin 1 analogs were 3"-fused in-frame with the reporter lichenase gene. The Tr2" weak constitutive promoter of Agrobacterium tumefaciens T-DNA and the strong constitutive promoter of the cauliflower mosaic virus 35S RNA gene were used as regulatory elements. The expression cassettes were used to transform agrobacteria and then introduced in tobacco leaf disks. On evidence of Southern hybridization, transgenic plants each carried a single copy of a hybrid gene, which corresponded in size to the constructed one. Zymography and Western blotting revealed full-length hybrid proteins in leaf extracts of transgenic plants. The results testified that plants can maintain and express synthetic genes for spider silks and, consequently, may be used as a convenient producer of recombinant silk analogs.     

Host-plant acceptance and performance of Tetranychus urticae (Acari, Tetranychidae)

Abstract: Tetranychus urticae is a serious pest of several crops worldwide. It performs differentially on diverse host‐plant species. Because dispersion is mainly passive, the process of host‐plant selection should be viewed in terms of host‐plant acceptance and not in terms of host finding. The objectives of this study were to investigate: (1) the acceptance of strawberry (S) in comparison with onion (O), leek (L) and parsley (P) by T. urticae; and (2) the suitability of these host plants for the performance of T. urticae, in terms of fecundity and survival. Host‐plant acceptance was measured through females that settled on a test plant or females that left for another host plant. In another experiment, for a duration of 5 days, individual newly mated females were assigned to discs of each host plant and the fecundity, the maximum number of offspring obtained from one female that settled on the disc, the survival and the percentage of females that oviposited at least one egg were analysed. A choice test to measure the preference of females for different host plants was performed. Movements took place towards (S) from the three plants: (O), (L) and (P). Mites significantly moved to other places in the Petri dishes from leek‐origin discs. Dispersal of T. urticae from (S) to other host‐plant discs was similar for all plants. Mean fecundity was higher on (S) than on the other plants. The maximum number of offspring per female was highest on (S), lowest on (L) and (O), and intermediate on (P). Survival of females and percentage of females that laid at least one egg were independent of the host plant. The choice test showed that oviposition was higher on (S) and (P) and very poor on (L) and (O) and that more females settled on (S) and (P). Although mites migrated from parsley to strawberry, the first host plant has a higher acceptance of T. urticae in terms of maximum number of offspring per female than onion and leek, and a lower performance in terms of fecundity than strawberry. Parsley could be a good candidate for an associate plant in a strawberry crop; however, it needs more research under field conditions.     

Physiological resistance and behavioral avoidance responses to residues of four pesticides by six spider mite populations

Six twospotted spider mite populations were assayed for their levels of physiological resistance and behavioral avoidance to residues of four synthetic pesticides. Mortality could not be estimated for bifenthrin and fenvalerate (synthetic pyrethroids) as mites effectively avoided treated surfaces, however significant between-population differences in mortality were detected for chlordimeform and cyhexatin. Considerable variation in walkoff and spindown behavioral response to sub-lethal doses of pesticides was observed among populations within compounds, and within populations among compounds. Within-compound walkoff and spindown behavioral response varied among all mite populations. Few significant between-compound correlations were significant, indicating that spider mites responded differently to the four pesticides. The hypothesis that physiological resistance is negatively correlated with behavioral avoidance was tested. Of the four possible negative correlations between physiological resistance and behavioral avoidance for chlordimeform and cyhexatin, only the correlation between cyhexatin-induced mortality and spindown response was significant. Comparisons of physiological resistance and behavioral avoidance of chlordimeform and cyhexatin by specific pairs of populations did not consistently find these two characters to be related. In a related experiment, the magnitude and direction of the correlation between physiological resistance and behavioral avoidance following selection for increased physiological tolerance to cyhexatin was compared in a highly resistant and a susceptible population of the twospotted spider mite. Mortality in the susceptible population at 2 ppm cyhexatin was similar to mortality in the resistant population at 250 ppm after 72h exposure (ca. 12%). However, at these concentrations, the resistant population exhibited much higher avoidance of the compound through walkoff response.     

Taste difference thresholds for sucrose in two species of nonhuman primates

The purpose of this study was to determine taste difference thresholds for sucrose in frugivorous spider monkeys and omnivorous baboons. Using a two‐bottle preference test of brief duration, we presented four Ateles geoffroyi and four Papio hamdryas anubis with six different reference concentrations (RCs) of 25, 50, 100, 200, 300, and 400 mM sucrose and tested their ability to discriminate these from lower concentrations of this carbohydrate. The just noticeable differences (JNDs), expressed as Weber ratios (Δ/I), were found to range from 0.075–0.25 in the spider monkeys, with a tendency for lower values with higher Rcs. In contrast, the baboons showed the reverse trend, with the lowest Weber ratio of 0.10 at the two lowest Rcs and higher values of up to 0.25 with the highest RC tested. Thus, the JNDs were found to be generally similar in both species and at least as low as in humans. The results support the assumption that both spider monkeys and baboons may use sweetness as a criterion for food selection. The different patterns of differential sensitivity for sucrose across the range of concentrations tested suggest a correlation between the ability to discriminate between different concentrations of sucrose and the dietary habits of the two species. Am. J. Primatol. 48:153–160, 1999. © 1999 Wiley‐Liss, Inc.     

Relationships among food and contact signals in experimental group‐living young of Tegenaria atrica

Relationships between the quantity of diet, and group vs. individual rearing toward ontogenesis on degree of cannibalism and cuticular lipid profile of young Tegenaria atrica Araneae, Agelenidae were studied. Ad libitum diet increases the development rate and decreases cannibalism between conspecifics compared to a reduced diet. Individually reared young on the two diets showed no quantitative differences in cuticular lipid profile, but differences were observed in individual vs. group rearing modes. The ad libitum–fed grouped young spiders had notably increased quantities of palmitic acid, 13,17‐,11,17‐, and 9,17‐dimethylhentriacontane, methyl oleate, and n‐heptatriacontane over the reduced diet, cannibalistic group. Arch. Insect Biochem. Physiol. 42:188–197, 1999. © 1999 Wiley‐Liss, Inc.     

Genetically engineered syntheses of tandem repetitive polypeptides consisting of glycine-rich sequence of spider dragline silk

We described genetically engineered syntheses of tandem repetitive polypeptides consisting of glycine-rich sequence, GlyLeuGlyGlyGlnGlyGlyGlyAlaGlyGlnGlyGlyTyrGly, designated SCAP(1), in spidroin I of spider dragline silk from Nephila clavipes and the secondary conformational analyses in the solid state by Fourier transform ir measurements. The polypeptides composed of 4, 5, 6, 7, 11, 12, or 13 repeats of SCAP(1) were expressed in Escherichia coli, purified by nickel chelate affinity chromatography, and then cleaved with cyanogen bromide to release N- and C-terminal extensions. Typical yields were from 1.2 to 5.2 mg of lyophilized uncleaved polypeptides per liter of fermentation medium at an absorbance of 2.0 at 600 nm, and the production levels increased with decreasing the molecular weight of the expressed polypeptides. The lyophilized powder of cleaved SCAP(13) adopted the random coil, whereas the cast film from formic acid formed the β-sheet structure. The conformational results might indicate that the glycine-rich sequence formed β-sheet structure in spidroin I. Cleaved SCAP(13) started to decompose under nitrogen at ca. 230°C, which was in agreement with the decomposition temperature of the spider dragline silk from N. clavipes. © 1998 John Wiley & Sons, Inc. Biopoly 45: 269–279, 1998     

Prey capture in Dysdera crocata (Araneae: Dysderidae), a long fanged spider

Abstract

The manner in which Dysdera crocata used its large chelicerae was described. Previous claims that the chelicerae are adaptations enabling the spider to penetrate the dorsal carapace of its prey (woodlice) were not supported.     

Effects of Ocimum basilicum and Ruta chalepensis hydrosols on Aphis gossypii and Tetranychus urticae

Hydrosols are by‐products derived during the extraction of essential oils and are produced in a high amount and at very low cost. Their effects on crop pests have been little studied, although recent studies have shown their insecticidal properties. In this work, the effects of hydrosols derived from Ocimum basilicum (sweet basil) and Ruta chalepensis (rue) were investigated on the serious crop pests Aphis gossypii and Tetranychus urticae. The main compounds of basil hydrosol were linalool (66.5%), eugenol (18.9%) and eucalyptol (7.1%), while rue's were 2‐nonanone and 2‐undecanone at 77.0% and 8.9%, respectively. The mortality and fecundity of A. gossypii and T. urticae were recorded for 7 days after application of hydrosols. Apterous adult aphids and female mites were sprayed on cucumber leaves in special structures. Both hydrosols caused significant mortality rates, which fluctuated between 46.0% and 64.0%. The negative control (deionized water) caused no mortality, while for the positive controls (synthetic pesticides) was 100%. The fecundity of A. gossypii and T. urticae was significantly reduced after the application of the hydrosols (17.1 nymphs of A. gossypii and 22.8 eggs for T. urticae had been produced per female after treated with the hydrosol of R. chalepensis and O. basilicum, in comparison with 41.6 and 49.5 in the negative controls, respectively). In conclusion, the hydrosols from both plants presented an important effect on the mortality and fecundity of both pests.     

From the laboratory to the field: contrasting effects of multi-trophic interactions and agroforestry management on coffee pest densities

Only few factors influencing pest populations can be studied in the laboratory, but many population‐driving factors interact in the field. Therefore, complementary laboratory and field approaches are required for reliable predictions of real‐world patterns and processes. Laboratory and field experiments with the red spider mite, Oligonychus ilicis McGregor (Acari: Tetranychidae), and the coffee leaf miner, Leucoptera coffeella Guérin‐Méneville (Lepidoptera: Lyonetiidae), on coffee plants, Coffea arabica L. (Rubiaceae), were combined to study the relative importance of biotic interactions, including resource preferences and natural‐enemy impact, and habitat factors, such as agroforestry type and management intensity, on coffee pest densities. In the laboratory, leaf discs cut from undamaged coffee plants were significantly preferred by red spider mites over those from plants infested with conspecific mites, leaf rust pathogens [Hemileia vastatrix Berkeley & Broome (Uredinales)], or coffee leaf miners, resulting in higher reproductive success. Similarly, undamaged plants were preferred by coffee leaf miners over red spider mite‐infested plants. However, in the field, red spider mite densities were positively correlated with coffee leaf miner and leaf rust densities, thereby contrasting with laboratory predictions. Hence, our study suggests that the importance of resource preferences and fitness expected based on laboratory experiments was suppressed by environmental conditions in the field, though other unassessed biotic interactions could also have played a role. Furthermore, intensified agroforestry was characterized by higher red spider mite densities, whereas densities of its major natural enemy, the predatory mite Amblyseius herbicolus Chant (Acari: Phytoseiidae), were not related to agroforestry management. Densities of coffee leaf miner and its main natural enemy, a eulophid parasitoid (Hymenoptera), were not affected by management practices. In conclusion, patterns found in the laboratory did not hold for the field, emphasizing the difficulties of extrapolating small‐scale experiments to larger spatial scales and the need to combine both approaches.     

Predator Interference and the Establishment of Generalist Predator Populations for Biocontrol

We conducted a field experiment to determine the extent to which interference among generalist predators limits their effectiveness as biocontrol agents. We manipulated immigration of a guild of actively hunting generalist ground predators, carabid beetles and lycosid spiders, by intercepting them as they attempted to enter fenced 50-m² vegetable gardens. Immigration was blocked, allowed at the mean rate measured at our field site, or doubled. Altered immigration rates were maintained through a spring garden of cabbage, bean, eggplant, and cucumber, followed by a summer garden of squash. We monitored densities of carabids and lycosids to discover if altering their immigration rate changed their densities in the plots. We also measured densities of other predators on the ground and in plant foliage, pest numbers, and vegetable yields. Doubling the immigration rate of carabids and lycosids approximately doubled the densities of carabids inside the plots, but did not increase lycosid densities. Increasing the rate of immigration of carabids and lycosids depressed densities of nonlycosid ground spiders. In the spring gardens, manipulation of carabid and lycosid immigration did not influence numbers of predators or herbivores in the foliage and did not affect vegetable productivity. In contrast, in the summer gardens, foliage-dwelling predators were lower, pest densities were marginally lower, and squash productivity was higher in the carabid and lycosid immigration plots compared to the no-immigration treatment. Doubling carabid and lycosid immigration rate never increased the magnitude of their effects on other predators, pests, or plant productivity. Predator interference limited lycosid establishment, reduced densities of other predator taxa, and apparently prevented a doubling of carabid densities from having an increased impact on pest numbers. Nevertheless, despite widespread effects of predator interference, allowing immigration of lycosids and carabids increased squash productivity.