On a habitat structure-based approach to evaluating species occurrence: cavity-nesting Hymenoptera in a secondary tropical forest remnant

Measuring bee and wasp community habitat preferences in natural systems may provide insights for biodiversity management and conservation as habitat heterogeneity can be the major factor affecting species diversity in a community. Here, we present evidence that supports the use of a vegetation structure-based approach in order to predict the occurrence of common Brazilian-remnant solitary bee and wasp species. Using trap nests, we sampled Aculeate bees and wasps in a forest remnant within an urban area of southeast Brazil. We also measured eight habitat structure components in the area. Tree trunk circumference, shrub and wood log abundance were good predictors of presence or absence of the commonest solitary bee and wasp species in the study area. We demonstrated that even on a small scale it is possible to detect significant influences of habitat structural features on species occurrences and that some of them are effective as surrogates for predicting trap-nesting Hymenoptera occurrence in a given area. Our data present evidence on the potential application of a habitat structure-based approach in conservation assessments concerning cavity-nesting Hymenoptera. We caution, however, that this habitat structure-based approach must to be taken with prudence as a detailed survey of an area’s biodiversity is always preferable.     

Predators mediate the effects of a fungal pathogen on prey: an experiment with grasshoppers,wolf spiders,and fungal pathogens

1. Prey interact with multiple kinds of enemies such as predators, parasites, and pathogens. Interactions among enemies can alter prey dynamics but they are often studied separately. 2. During the summers of 2005–2006, we conducted a field experiment to examine interactions among grasshoppers, spider predators, and a lethal fungal pathogen of grasshoppers. Grasshopper nymphs were stocked into field enclosures. Predation was manipulated by adding spiders to enclosures on day 1, day 5, or day 10 of the experiment, or no spiders were added. We monitored grasshopper survival and grasshopper mortality from fungal pathogens for 4 weeks. 3. Fungal pathogens were abundant in 2005 but not in 2006, probably because of favourable weather conditions in 2005. When fungal pathogens were abundant, spider presence reduced grasshopper mortality from fungal pathogens, but only when spiders were present early in the experiment (added on day 1 or day 5). 4. The outcome of predator–prey interactions varied between years, probably as a result of differences in pathogen prevalence. In 2005, spider presence reduced the number of deaths from the pathogen, leading to a slight trend of increased grasshopper density. However, in 2006, when pathogens were not an important source of mortality, spider predation was compensatory.     

悦目金蛛3种蛛丝超微结构和理化特性的初步研究

利用扫描电镜、氨基酸分析仪、X-衍射仪和单纤维电子强力仪分别对悦目金蛛Argiopeamoena拖丝、网框丝和卵袋丝的超微结构和理化特性进行了测试和观察。结果表明,悦目金蛛卵袋不是由一种结构均一的丝纤维构成,而是由直径相差悬殊的Ⅰ型卵袋丝和Ⅱ型卵袋丝2种丝纤维共同组成,该结果对卵袋丝仅由管状腺产生的观点提出了疑问。在氨基酸组成上悦目金蛛拖丝和网框丝相似,但其卵袋丝的氨基酸组成与拖丝和网框丝相比差别明显。另外还发现卵袋丝的强度、结晶度大于拖丝和网框丝,而它的延伸性能却不及拖丝和网框丝。     

甘肃子午岭天然次生林区三种植被类型中土壤蜘蛛群落的组成及多样性

2004年4—10月,在甘肃子午岭天然次生林区采用巴氏诱罐法采集土壤蜘蛛2164头,隶属于19科43种。研究表明辽东栎林(Quercusliaotungensis)、油松林(Pinustabulaeformis)和杨树林(Populusdavidiana)3种森林植被类型中土壤蜘蛛群落组成有明显的差异;不同生境蜘蛛群落的组成成分和多样性指数各异;从各生境中捕获的蜘蛛个体数量分析,皿蛛科、平腹蛛科和科狼蛛科的数量最多,优势类群的组成相似;各生境类型中蜘蛛功能集团的组成及多样性也有明显差异。同时,分析了影响蜘蛛群落组成和多样性的主要因子是生境的植被类型和生境异质性。     

Intragroup lethal aggression in wild spider monkeys

We report the first evidence of intragroup coalitionary aggression leading to the death of a wild young adult male spider monkey. During a long-term study of a well-habituated community at the Otoch Ma'ax Yetel Kooh reserve in Yucatan, Mexico, a young adult male sustained severe injuries repeatedly between January and March 2002. On 1 April 2002 the same male was the victim of an intragroup attack by at least one adult male that resulted in his death. We highlight several causes of intragroup aggression that may account for the killing.     

Lethal intragroup aggression by adult male spider monkeys (Ateles geoffroyi)

I report three cases of coalitionary aggression by adult male black-handed spider monkeys (Ateles geoffroyi) against subadult males within their community on Barro Colorado Island (BCI), Panama. Two of these cases were followed by the disappearance and presumed death of the victim. Similar behavior was recently reported by Valero et al. [in press], who suggested that this behavior may be the result of intense male reproductive competition. Like the single instance they reported, the cases I report all occurred when the operational sex ratio was approximately 1:1, which suggests that intense competition among males for access to reproductively viable females may be a contributing factor. Additionally the very low density of spider monkeys on BCI may play a significant role in the occurrence of this lethal aggression. Large numbers of adult males are not necessary to protect a territorial boundary against neighboring groups, and additional males may act merely as mating competition.     

Movement of the twospotted spider mite, Tetranychus urticae, among hosts in a corn-peanut agroecosystem

A 3 year study of spider mites in a corn-peanut agroecosystem indicated that the persistance and pest status of mite populations depended on dispersal among a succession of temporarily suitable cultivated and non-cultivated hosts. In the spring, mites crawled from overwintering sites in vegetation along field margins into both peanut and corn fields, but became established only in corn. Initiation of aerial dispersal from corn was coincident with and appeared dependent upon mites moving to the top of the corn canopy, where they were exposed to the wind. Mites were first observed in peanut immediately following the onset of aerial dispersal from corn, and these aerial dispersers were the primary source of subsequent mite infestations in peanut. As populations grew in peanut, mites dispersed into vegetation along peanut field margins and became the nucleus of populations which persisted over the winter. This pattern of host utilization was reinitiated in the spring if corn was planted adjacent to infested field borders. This pattern commonly occurs since corn is planted following peanut in the predominant crop rotation sequence in this area.

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Résumé Des populations d'acariens ont été étudiées pendant 3 ans sur maïs, arachide et végétation spontanée, dans 7 fermes commerciales de Chowan Co., Caroline du Nord. Les déplacements d'acariens parmi ces plantes ont été notés en fonction de la croissance de la population et de la phénologie des hôtes. Un schéma cohérent de croissance de la population d'acariens et de leurs mouvements en découle, dont seule la taille change suivant les fermes et les années. Les acariens provenant de populations hivernantes sur la végétation spontanée bordant les champs migrèrent dans les champs cultivés adjacents quelle qu'en soit la nature de la culture. Cependant, à cette époque, les populations d'acariens ne s'établissaient que dans le maïs. Dans le maïs, les acariens se répandirent à travers le champ et se multiplièrent sur des pieds particuliers jusqu'à ce qu'ils eussent atteint le sommet de la canopée du maïs. Les premiers acariens transportés par le vent ont été capturés la semaine suivant la première apparition d'acariens au sommet de la canopée du maïs et aussitôt après la découverte des premiers acariens dans les arachides voisines. Ceci suggère que les acariens dispersés par le vent sont à l'origine des contaminations ultérieures des arachides voisines. Plus tard dans la saison, les acariens se dispersèrent à partir de l'arachide vers les sites d'hibernation dans la végétation spontanée poussant autour du champ d'arachide. Puisque des champs semés en arachides sont généralement semés en maïs l'année suivante, les acariens se dispersant au printemps depuis les sites d'hibernation rencontrèrent souvent du maïs qu'ils colonisèrent. Ce cycle répétitif d'utilisation de l'hôte et de dispersion est considéré comme fortement responsable de la pérennité des acariens et de leur danger potentiel dans les agroécosystèmes à maïs-arachide, caractéristiques du canton de Chowan (N.C.).Les problèmes potentiels posés par les acariens sur arachide ont paru être liés à l'intensité de l'attaque d'acariens sur le maïs voisin, qui sert de réservoir pour les populations d'acariens. Ceci suggère que le contrôle des populations d'acariens sur maïs peut être une stratégie viable pour limiter les infestations ultérieures sur arachide et, en dernier lieu, les populations hivernantes.

     

Role of the entomogenous fungus, Neozygites floridana, in population declines of the twospotted spider mite, Tetranychus urticae, on field corn

In field plots in which populations of predaceous species were suppressed using carbaryl, populations of the twospotted spider mite, Tetranychus urticae Koch, on field corn declined in association with aerial dispersal of the mites or with epizootics of the entomogenous fungus, Neozygites floridana Weiser & Muma. The relative importance of these two factors varied from year to year depending on environmental conditions. When moist weather conditions induced epizootics of N. floridana before corn plants became heavily infested with mites, the pathogen appeared to be the major factor causing mite population declines. When dry weather conditions allowed mite populations to expand unchecked until corn plants became entirely infested, mite aerial dispersal was the major factor associated with mite population declines. In every field in which there was an epizootic of N. floridana, routine applications of the fungicide maneb delayed epizootics and reduced or delayed the impact of the pathogen on mite populations. The total number of Neozygites-infected mites produced in maneb-treated plots throughout the test period was significantly greater than that in untreated plots when epizootics were initiated during periods of mite population growth. Fewer total infected mites were produced in maneb-treated plots compared to untreated plots when epizootics were initiated during periods of mite population decline.

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Résumé Dans des parcelles de maïs dont les populations d'espèces prédatrices avaient été éliminées par du carbaryl, des populations de T. urticae ont régressé en fonction de la dispersion aérienne des acariens ou d'épizooties provoquées par N. floridana. L'importance relative de ces deux causes varie d'année suivant les conditions écologiques. Le pathogène paraissait la principale cause de déclin des populations quand le temps humide a induit les épizooties par N. floridana avant que le maïs n'ait été largement contaminé par les acariens. Quand le temps sec a permis aux populations d'acariens de se développer sans frein jusqu'à contamination totale du maïs, la dispersion aérienne des acariens était la principale cause de déclin des populations d'acariens. Dans tous les champs où il y avait eu épizootie de N. floridana, des traitements de routine avec le fongicide meneb ont retardé les épizooties et réduit ou retardé l'impact du pathogène sur les populations d'acariens. Pendant toute la période d'étude, le nombre total d'acariens infestés par Neozygites était significativement plus élevé dans les parcelles traitées au maneb que dans les parcelles non traitées, lorsque les épizooties étaient provoquées pendant la période de croissance des populations d'acariens. Quand les épizooties ont été déclenchées pendant la période de déclin des populations d'acariens, un nombre plus faible d'acariens infestés était observé dans les parcelles traitées au maneb que dans les parcelles sans traitement.