Browsing by Author "Zaviezo, T"

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    Aspects of the biology of Hyssopus pallidus (Hymenoptera : Eulophidae), a parasitoid of the codling moth (Lepidoptera : Olethreutidae)
    (ENTOMOL SOC AMER, 1999) Zaviezo, T; Mills, N
    Hyssopus pallidus (Askew) is a gregarious ectoparasitoid that attacks 2nd-instar to prepupal codling moth. Host attack includes initial probing, host paralysis, oviposition from 2 to 30 ears per host, nondestructive host feeding, and brood guarding. The development rate of the immature stages increased with temperature, with a life cycle minimum threshold of 10 degrees C and a maximum threshold between 30-35 degrees C. Female development time from oviposition to adult emergence decreased from 39 d at 15 degrees C to 12 d at 30 degrees C. Female longevity decreased from 115 d at 15 degrees C to 40 d at 30 degrees C, and was significantly increased by provision of honey, but not by host feeding. Lifetime fecundity was estimated to be lm eggs, with a female-biased progeny sex ratio of 0.58 males and 13.02 females per host. The presence of a Ist female guarding her brood did not prevent or influence the level of superparasitism by a 2nd female; experienced females were less likely to superparasitize than naive females, and superparasitism was most frequent among bloods 24 h old. The host specificity of H. pallidus was tested using no-choice tests with 5 common orchard Microlepidoptera. It successfully attacked and developed on 100% of codling moth larvae and 60% of orange tortrix larvae. It paralyzed but did not oviposit on 20% of Pandemis pyrusana Kearfott larvae. and it did not attack obliquebanded leafroller or navel orangeworm.
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    Factors influencing the evolution of clutch size in a gregarious insect parasitoid
    (WILEY-BLACKWELL, 2000) Zaviezo, T; Mills, N
    1. In this study we examined the clutch size of Hyssopus pallidus (Askew) (Hymenoptera, Eulophidae), a gregarious ectoparasitoid of codling moth (Lepidoptera, Tortricidae) larvae that is characterized by a host handling time of 2 days approximately.
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    Ladybird (Coleoptera : Coccinellidae) dispersal in experimental fragmented alfalfa landscapes
    (CZECH ACAD SCI, INST ENTOMOLOGY, 2005) Grez, AA; Zaviezo, T; Rios, M
    Habitat fragmentation may affect the dispersal behaviour of individuals across the landscape. If there is a high boundary contrast between the remaining fragments and the matrix, individuals should tend to stay inside the fragments, but the configuration of the landscape, i.e. the level of fragmentation and isolation distance between fragments, may modulate this. To test these ideas, we made several mark-recapture experiments with the ladybird Eriopis connexa (Germ.) in manipulated alfalfa model landscapes (30 x 30 m). Specifically we evaluated (i) ladybird movement and permanence in alfalfa and bare ground areas, (ii) how they move across fragment/matrix boundaries, (iii) how their movement between fragments within a landscape is affected by fragmentation level and isolation distance, and (iv) how their permanence in the landscape is affected by fragmentation Ievel and isolation distance. The fragmented alfalfa landscapes had a constant level of habitat loss (84%), but varied in the level of habitat fragmentation (4 or 16 fragments), and isolation distance between fragments (2 or 6 m). We also sampled aphid abundance in the different landscapes through time. We found that ladybirds stay longer and displace less in alfalfa than on bare ground, and that they move less from the alfalfa fragments to the neighbouring bare ground matrix than vice versa. At the landscape level, ladybirds had a higher inter-fragment movement when fragments were closer, they tended to remain in less fragmented landscapes, regardless of their isolation distance. Aphid abundance increased in time, but it was similar in all landscapes. Ladybird movement within fragments, in the matrix and in the boundary between both habitats explains why ladybirds concentrate within alfalfa fragments. However, their dispersal movements at the landscape level do not reflect the higher abundance sometimes found for several species of ladybirds in more fragmented landscapes. At this larger scale, other mechanisms may have a stronger influence in determining the abundance of ladybirds.
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    Mechanisms affecting population density in fragmented habitat
    (RESILIENCE ALLIANCE, 2005) Tischendorf, L; Grez, A; Zaviezo, T; Fahrig, L
    We conducted a factorial simulation experiment to analyze the relative importance of movement pattern, boundary-crossing probability, and mortality in habitat and matrix on population density, and its dependency on habitat fragmentation, as well as inter-patch distance. We also examined how the initial response of a species to a fragmentation event may affect our observations of population density in post-fragmentation experiments. We found that the boundary-crossing probability from habitat to matrix, which partly determines the emigration rate, is the most important determinant for population density within habitat patches. The probability of crossing a boundary from matrix to habitat had a weaker, but positive, effect on population density. Movement behavior in habitat had a stronger effect on population density than movement behavior in matrix. Habitat fragmentation and inter-patch distance may have a positive or negative effect on population density. The direction of both effects depends on two factors. First, when the boundary- crossing probability from habitat to matrix is high, population density may decline with increasing habitat fragmentation. Conversely, for species with a high matrix-to-habitat boundary- crossing probability, population density may increase with increasing habitat fragmentation. Second, the initial distribution of individuals across the landscape: we found that habitat fragmentation and inter-patch distance were positively correlated with population density when individuals were distributed across matrix and habitat at the beginning of our simulation experiments. The direction of these relationships changed to negative when individuals were initially distributed across habitat only. Our findings imply that the speed of the initial response of organisms to habitat fragmentation events may determine the direction of observed relationships between habitat fragmentation and population density. The time scale of post-fragmentation studies must, therefore, be adjusted to match the pace of post-fragmentation movement responses.
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    Short-term effects of habitat fragmentation on the abundance and species richness of beetles in experimental alfalfa microlandscapes
    (SOC BIOLGIA CHILE, 2004) Grez, AA; Zaviezo, T; Reyes, S
    Habitat loss and fragmentation are considered as the main causes of biodiversity depression. Habitat loss implies a reduction of suitable habitat for organisms, and habitat fragmentation is a change in the spatial configuration of the landscape, with the remaining fragments resulting more or less isolated. Recent theory indicates that the effects of habitat loss are more important than those of habitat fragmentation, however there are few experimental studies evaluating both processes separately. To test the effects of habitat fragmentation per se on the abundance, species richness and diversity of epigeal coleopterans, 15 (30 x 30 m) alfalfa microlandscapes, distributed in three blocks, were created. On twelve of them, 84 % of the habitat was removed, leaving in each landscape four or 16 fragments separated by 2 or 6 m of bare ground. From December 2002 to April 2003, before and after fragmentation, coleopterans were sampled using pitfall traps. In total, 8,074 coleopterans of 75 species belonging to 16 families were captured. Neither habitat fragmentation nor habitat loss affected the total abundance of coleopterans, with the exception of Anthicidae that was more abundant in the microlandscapes composed by four fragments separated by 2 m. This family was also more abundant in the matrix of fragmented microlandscapes, while most other beetle families were more abundant in the fragments, significantly Carabidae and Lathridiidae. Species richness (per trap and per landscape) was higher in microlandscapes with 16 fragments separated by 6 m. Contrary to what is described frequently in the literature, habitat fragmentation did not negatively affect the abundance or the species richness of epigeal coleopterans. Rather, smaller and more isolated alfalfa fragments seem to provide habitat to support greater biodiversity. These results agree with more recent findings where habitat fragmentation per se seems not to have deleterious effects on the fauna, instead, it could favor the biota, at least at short time scales.