Resistance against spider mites in cotton induced by mechanical abrasion

Mechanical abrasion of cotyledons induced resistance to spider mites (Tetranychus urticae Koch) in cotton plants in four of six replicates. Mite population grwoth was reduced on plants that had either been abraded or had been previously exposed to mite feeding, compared to undamaged controls. Populations of mites were not different for plants that were abraded and for those that had been exposed previously to mites. In two of the six replicates, mite populations were not different for abraded, previously exposed and control plants. In these two replicates, densities of mites were greater than in the four replicates in which abrasion and previous exposure were effective, although the reasons for this discrepancy are not known.Induction of resistance by mechanical abrasion indicates that the response is not caused only by some factor specific to mites but can be caused by general wounding.

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Résumé L'abrasion mécanique des cotylédons a induit la résistance aux acariens (Tetranychus urticae) sur des pieds de coton dans 4 répétitions sur 6. La croissance des populations d'acariens sur plantes abrasées ou précédemment exposées à l'alimentation des acariens, était plus faible que celle des témoins. Les populations d'acariens sur plantes abrasées et sur plantes exposées précédemment aux acariens ne différaient pas. Dans 2 des 6 lots, les populations d'acariens ne différaient pas sur plantes abrasées, précédemment exposées ou témoin. Dans ces 2 lots, les densités d'acariens étainet plus élevées que dans les 4 autres, où l'abrasion et l'exposition antérieure étaient efficaces, bien ce que les raisons de cette discordance soient inconnues. L'induction de la résistance par une abrasion mécanique montre que la réaction n'est pas provoquée seulement par quelque facteur spécifique pour les acariens, mais par une réponse générale aux blessures.

     

Leaf drop affects herbivory in oaks

Leaf phenology is important to herbivores, but the timing and extent of leaf drop has not played an important role in our understanding of herbivore interactions with deciduous plants. Using phylogenetic general least squares regression, we compared the phenology of leaves of 55 oak species in a common garden with the abundance of leaf miners on those trees. Mine abundance was highest on trees with an intermediate leaf retention index, i.e. trees that lost most, but not all, of their leaves for 2–3 months. The leaves of more evergreen species were more heavily sclerotized, and sclerotized leaves accumulated fewer mines in the summer. Leaves of more deciduous species also accumulated fewer mines in the summer, and this was consistent with the idea that trees reduce overwintering herbivores by shedding leaves. Trees with a later leaf set and slower leaf maturation accumulated fewer herbivores. We propose that both leaf drop and early leaf phenology strongly affect herbivore abundance and select for differences in plant defense. Leaf drop may allow trees to dispose of their herbivores so that the herbivores must recolonize in spring, but trees with the longest leaf retention also have the greatest direct defenses against herbivores.     

Induced resistance against spider mites in cotton: Field verification

Cotton plants that had been damaged by spider mites (Tetranychus spp.) or by mechanical abrasion at the cotyledon stage were less likely to develop infestations of spider mites compared to controls early in the season. These are the first field results to demonstrate that induced resistance can reduce pest populations in an agricultural system. Differences in mite populations early in the season caused by induced resistance did not translate into differences in plant growth or cotton yield at harvest.

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Vérification au champ de la résistance du coton induite par les acariens

Résumé Les plants de coton qui ont été endommagées, au stade cotylédons, par des acariens ou par une abrasion mécanique, ont moins de chance que les témoins, de présenter ultérieurement des dégats dus aux acariens. C'est la première fois que des résultats montrent qu'une résistance induite peut réduire les populations dans un agrosystème. Les différences ultérieures dans les populations d'acariens, ne transparaissent pas au niveau de la croissance du coton ou de la production au moment de la récolte.

     

Cross-talk between jasmonate and salicylate plant defense pathways: effects on several plant parasites

Plants are often attacked by many herbivorous insects and pathogens at the same time. Two important suites of responses to attack are mediated by plant hormones, jasmonate and salicylate, which independently provide resistance to herbivorous insects and pathogens, respectively. Several lines of evidence suggest that there is negative cross-talk between the jasmonate and salicylate response pathways. This biochemical link between general plant defense strategies means that deploying defenses against one attacker can positively or negatively affect other attackers. In this study, we tested for cross-talk in the jasmonate and salicylate signaling pathways in a wild tomato and examined the effects of cross-talk on an array of herbivores of cultivated tomato plants. In the wild cultivar, induction of defenses signaled by salicylate reduced biochemical expression of the jasmonate pathway but did not influence performance of S. exigua caterpillars. This indicates that the signal interaction is not a result of agricultural selection. In cultivated tomato, biochemical attenuation of the activity of a defense protein (polyphenol oxidase) in dual-elicited plants resulted in increased of performance of cabbage looper caterpillars, but not thrips, spider mites, hornworm caterpillars or the bacteria Pseudomonas syringae pv. tomato. In addition, we tested the effects of jasmonate-induced resistance on the ability of thrips to vector tomato spotted wilt virus. Although thrips fed less on induced plants, this did not affect the level of disease. Thus, the negative interaction between jasmonate and salicylate signaling had biological consequences for two lepidopteran larvae but not for several other herbivores tested or on the spread of a disease.     

Volatile communication among sagebrush branches affects herbivory: timing of active cues

Airborne communication can affect systemic induced resistance to herbivory on neighboring branches and individual plants. Sagebrush is the best known example of this phenomenon although the mechanisms of this communication system remain unidentified. We do not know the timing of emission or the chemical nature of the active cue. We investigated the timing of this phenomenon by using plastic bags to prevent propagation of volatile compounds and experimentally manipulated the timing of removal of these bags. We found that blocking the volatiles prevented systemic induced resistance. Experimentally allowing clipped branches to release cues for up to 3 days after clipping caused a reduction in damage in neighboring branches on the clipped plants. This indicates that active cues are released from the time we clipped for the next 3 days or that cues released immediately remained active over this time period. As we continue to evaluate potential chemicals as active cues in plant communication, this prolonged effectiveness may provide an important screen against which to evaluate any putative signals. Handling editor: Robert Glinwood     

Effects of an early-season folivorous moth on the success of a later-season species,mediated by a change in the quality of the shared host,Lupinus arboreus Sims

Summary Larvae of Platyprepia virginalis (Lep.: Arctiidae) and Orgyia vetusta (Lep.: Lymantriidae) feed on the foliage of bush lupine (Lupinus arboreus Sims) at Bodega Bay, California, USA, in February–April and May–July, respectively. Female O. vetusta attained lower pupal weights and produced fewer eggs on branches of L. arboreus which had experimentally received P. virginalis damage earlier in the same year, compared to those reared on control branches.Growth rates of first-instar O. vetusta were lower on undamaged leaves of previously damaged L. arboreus than on leaves of undamaged controls. This was true for lupine bushes damaged by P. virginalis in the field; and also for greenhouse-grown lupine plants damaged by Estigmene acrea (Lep.: Arctiidae) when excised foliage was used in the assay. However, fifth (last) instar female O. vetusta larvae showed no preference for damaged versus undamaged greenhouse-grown L. arboreus in their feeding or choice of a site for pupation.These experiments demonstrate the potential for competition-like interactions between herbivores mediated by changes in quality of the shared host.     

Preparation of N-nosyl-3,4-epimines derived from levoglucosan by sodium borohydride reduction

Starting from 1,6-anhydro-beta-d-glucopyranose 1 (levoglucosan), N-o-nitrobenzenesulfonyl (nosyl) 3,4-epimino derivatives with d-allo, d-galacto, and d-talo configurations have been prepared via NaBH(4) reduction of suitably substituted azido tosylates. The benefits and limitations of this method over the classical LiAlH(4) reduction method are discussed.     

Sequence of a cDNA for mouse thymidylate synthase reveals striking similarity with the prokaryotic enzyme

We report the nucleotide sequence of a cloned cDNA, pMTS-3, that contains a 1-kb insert corresponding to mouse thymidylate synthase (E.C. 2.1.1.45). The open reading frame of 921 nucleotides from the first AUG to the termination codon specifies a protein with a molecular mass of 34,962 daltons. The predicted amino acid sequence is 90% identical with that of the human enzyme. The mouse sequence also has an extremely high degree of similarity (as much as 55% identity) with prokaryotic thymidylate synthase sequences, indicating that thymidylate synthase is among the most highly conserved proteins studied to date. The similarity is especially pronounced (as much as 80% identity) in the 44-amino-acid region encompassing the binding site for deoxyuridylic acid. The cDNA sequence also suggests that mouse thymidylate synthase mRNA lacks a 3' untranslated region, since the termination codon, UAA, is followed immediately by a poly(A) segment.