154 research outputs found
Self-compensation in semiconductors: The Zn vacancy in Ga-doped ZnO
Self-compensation, the tendency of a crystal to lower its energy by forming point defects to counter the effects of a dopant, is here quantitatively proven. Based on a new theoretical formalism and several different experimental techniques, we demonstrate that the addition of 1.4 × 10 exp 21-cm exp −3 Ga donors in ZnO causes the lattice to form 1.7 × 10 exp 20-cm exp −3 Zn-vacancy acceptors. The calculated VZn formation energy of 0.2 eV is consistent with predictions from density functional theory. Our formalism is of general validity and can be used to investigate self-compensation in any degenerate semiconductor material.Peer reviewe
Nonhost diversity and density reduce the strength of parasitoid-host interactions
This is the final version of the article. Available from Wiley via the DOI in this record.The presence of nonprey or nonhosts is known to reduce the strength of consumer- resource interactions by increasing the consumer's effort needed to find its resource. These interference effects can have a stabilizing effect on consumer-resource dynamics, but have also been invoked to explain parasitoid extinctions. To understand how nonhosts affect parasitoids, we manipulated the density and diversity of nonhost aphids using experimental host-parasitoid communities and tested how this affects parasitation efficiency of two aphid parasitoid species. To further study the behavioral response of parasitoids to nonhosts, we tested for changes in parasitoid time allocation in relation to their host-finding strategies. The proportion of successful attacks (attack rate) in both parasitoid species was reduced by the presence of nonhosts. The parasitoid Aphidius megourae was strongly affected by increasing nonhost diversity with the attack rate dropping from 0.39 without nonhosts to 0.05 with high diversity of nonhosts, while Lysiphlebus fabarum responded less strongly, but in a more pronounced way to an increase in nonhost density. Our experiments further showed that increasing nonhost diversity caused host searching and attacking activity levels to fall in A. megourae, but not in L. fabarum, and that A. megourae changed its behavior after a period of time in the presence of nonhosts by increasing its time spent resting. This study shows that nonhost density and diversity in the environment are crucial determinants for the strength of consumer-resource interactions. Their impact upon a consumer's efficiency strongly depends on its host/prey finding strategy as demonstrated by the different responses for the two parasitoid species. We discuss that these trait-mediated indirect interactions between host and nonhost species are important for community stability, acting either stabilizing or destabilizing depending on the level of nonhost density or diversity present.This research was funded by NERC (grant no. NE/K005650/1) to F. J. F. van Veen. E. Frago was funded by Marie Curie Intra-European Fellowship within the 7th European Community Framework Programme (FP7-PEOPLE-2012-IEF #329648), and by CIRAD
Relationship between number of ovipositions of Cotesia flavipes (Cam.) and number of descendants emerged from its host Diatraea saccharalis (Fabr.)
Genetic diversity and host alternation of the egg parasitoid Oencyrtus pityocampae between the pine processionary moth and caper bug
Research ArticleThe increased use of molecular tools for species identification in recent decades revealed
that each of many apparently generalist parasitoids are actually a complex of morphologically
similar congeners, most of which have a rather narrow host range. Ooencyrtus pityocampae
(OP), an important egg parasitoid of the pine processionary moth (PPM), is
considered a generalist parasitoid. OP emerges from PPM eggs after winter hibernation,
mainly in spring and early summer, long before the eggs of the next PPM generation occurs.
The occurrence of OP in eggs of the variegated caper bug (CB) Stenozygum coloratum in
spring and summer suggests that OP populations alternate seasonally between PPM and
CB. However, the identity of OP population on CB eggs seemed uncertain; unlike OP-PPM
populations, the former displayed apparently high male/female ratios and lack of attraction
to the PPM sex pheromone. We studied the molecular identities of the two populations
since the morphological identification of the genus Ooencyrtus, and OP in particular, is difficult.
Sequencing of COI and ITS2 DNA fragments and AFLP analysis of individuals from
both hosts revealed no apparent differences between the OP-PPM and the OP-CB populations
for both the Israeli and the Turkish OPs, which therefore supported the possibility of
host alternation. Sequencing data extended our knowledge of the genetic structure of OP
populations in the Mediterranean area, and revealed clear separation between East and
West Mediterranean populations. The overall level of genetic diversity was rather small,
with the Israeli population much less diverse than all others; possible explanations for this
finding are discussed. The findings support the possibility of utilizing the CB and other hosts
for enhancing biological control of the PPMinfo:eu-repo/semantics/publishedVersio
Alternative food and biological control by generalist predatory mites: the case of Amblyseius swirskii
The genus Brachygrammatella Girault (Hymenoptera: Trichogrammatidae)
Volume: 44Start Page: 289End Page: 29
Dahmsia, a new genus of Mymaridae. (Hymenoptera: Chalcidoidea)
Volume: 51Start Page: 254End Page: 25
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