Tatiana Pina

Aboveground plant performance is strongly influenced by belowground microorganisms, some of which are pathogenic and have negative effects, while others, such as nitrogen-fixing bacteria and arbuscular mycorrhizal fungi, usually have positive effects. Recent research revealed that belowground interactions between plants and functionally distinct groups of microorganisms cascade up to aboveground plant associates such as herbivores and their natural enemies. However, while functionally distinct belowground microorganisms commonly co-occur in the rhizosphere, their combined effects, and relative contributions, respectively, on performance of aboveground plant-associated organisms are virtually unexplored. Here, we scrutinized and disentangled the effects of free-living nitrogen-fixing (diazotrophic) bacteria Azotobacter chroococcum (DB) and arbuscular mycorrhizal fungi Glomus mosseae (AMF) on host plant choice and reproduction of the herbivorous two-spotted spider mite Tetranychus urticae on common bean plants Phaseolus vulgaris. Additionally, we assessed plant growth, and AMF and DB occurrence and density as affected by each other. Both AMF alone and DB alone increased spider mite reproduction to similar levels, as compared to the control, and exerted additive effects under co-occurrence. These effects were similarly apparent in host plant choice, that is, the mites preferred leaves from plants with both AMF and DB to plants with AMF or DB to plants grown without AMF and DB. DB, which also act as AMF helper bacteria, enhanced root colonization by AMF, whereas AMF did not affect DB abundance. AMF but not DB increased growth of reproductive plant tissue and seed production, respectively. Both AMF and DB increased the biomass of vegetative aboveground plant tissue. Our study breaks new ground in multitrophic belowground-aboveground research by providing first insights into the fitness implications of plant-mediated interactions between interrelated belowground fungi-bacteria and aboveground herbivores.

ABSTRACT Tetranychus urticae Koch (Acari: Tetranychidae) populations in citrus can be regulated through the management of the cover crop. A mono-specific cover of the grass Festuca arundinacea Schreber (Poaceae) enhanced the diversity and abundance of Phytoseiidae mites compared with a multifloral cover. This increase resulted in a better control of T. urticae. Pollen availability and quality could be behind this result. Whereas multifloral cover offers a long-term source of a wide variety of pollen, F. arundinacea offers one single type of pollen in spring only. As a consequence, the generalist pollen feeder Euseius stipulatus (Athias-Henriot), which is a superior intra-guild predator, is highly favored in multifloral covers. Therefore, poor quality pollen may prevent pollen feeders from reaching high numbers and indirectly benefit T. urticae control by specialist phytoseiids.

ABSTRACT Tetranychus urticae Koch (Acari: Tetranychidae) is a key pest of clementine mandarins, Citrus clementina Tanaka (Rutaceae), in Spain. This mite is highly polyphagous and can be easily found in clementine orchards, both in the trees and in the associated flora. In a previous study we found that the use of a cover of Festuca arundinacea Schreber (Poaceae) offered a better regulation of T. urticae populations than either bare soil or the traditional wild cover, which included a mix of weed species. We hypothesized that the selection of two host races of T. urticae, specialized in F. arundinacea and C. clementina, could partly explain the results obtained in field studies (bottom-up regulation). Reciprocal transplant experiments show that sympatric deme × host combinations had higher mean fitness values for most of the parameters evaluated than the allopatric combinations in clementine, but not in F. arundinacea. Because local adaptation implies mean deme fitness to be systematically higher for the sympatric deme × habitat combinations than for the allopatric ones, these results can be taken as indicative of occurrence of local adaptation in T. urticae. Molecular genetic analyses with microsatellite markers support this conclusion and indicate that host adaptation of T. urticae found in our system may indeed contribute to a better natural regulation of this mite.

ABSTRACT The highly polyphagous Tetranychus urticae Koch is a key pest of Spanish clementine mandarins. This mite may be effortlessly found in clementine orchards, on the trees and also on the associated flora. In this chapter we discuss the suitability of a cover of the grass Festuca arundinacea Schreber (Poaceae) to enhance biological control of T. urticae relative to bare soil or a wild soil cover in citrus orchards. On the one hand, we hypothesize that the natural selection of a local strain of this mite specialized in F. arundinacea could result in an unsuccessful colonization of the associated trees. On the other hand, phytoseiid predatory mites specialized in T. urticae are regularly found in that cover and this presence may account for the better regulation of T. urticae populations in citrus orchards grown using this grass as a cover crop. Contrarily, regular provision of highly nutritious pollen for omnivorous phytoseiid mites in a wild cover relative to a F. arundinacea cover (which produces low quality pollen for phytoseiids and only in the spring), could support the higher abundance of phytoseiids with generalist pollen feeding habits in orchards grown in association with a wild cover. As a consequence, increased competition and/or intraguild predation from these generalists on more efficient T. urticae-specialized phytoseiids could seriously reduce their numbers or even make them disappear from the system. This fact, in combination with periods of prey scarcity in the orchard, could result in the permanent disappearance of T. urticae-specialized phytoseiids, leading to a deficient control of tetranychids in orchards with a wild cover.

Resumen: Un tercio de las plagas que atacan a los cítricos se incluye en el orden Homoptera. El orden Homoptera constituye un tercio de las plagas que atacan a los cítricos. Destacan las cochinillas diaspinas, las cochinillas blandas, los margarodinos, los ...

Cover crops can serve as reservoir of natural enemies by supplying alternative food sources as pollen. Our group has recently shown that a more diverse and efficient phytoseiid community is found in clementine trees associated with a mono-specific cover of the ...

The presence of the endoparasitoid Comperiella lemniscata on red citrus scale (Chrysomphalus dictyospermi) is recorded from citrus trees in Moncada, Valencia, Spain. Some biological features of Comperiella lemniscata and a key to separate both ...

Petroleum-derived spray oils (PDSOs) offer an interesting alternative to acaricides to control the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), a key pest of clementine mandarins, Citrus reticulata Blanco. However, there is a lack of knowledge on how these products should be used. In this study, we evaluated the efficacy of four PDSOs (Sunspray Ultrafine, Volck Miscible, Texaco D-C-Tron Plus, and Agroaceite) at five concentrations (0.5, 1.0, 1.5, 2.0, and 3.0%) against eggs, protonymphs, and adults of T. urticae. We also characterized the PDSOs deposition pattern to find out the possible relationship between this factor and efficacy. In general, for all PDSO assayed, the higher the concentration, the higher the coverage, the mean area of impacts and efficacy on T. urticae. The biggest mean area of the impacts corresponded to Texaco D-C-Tron Plus. This PDSO was the most effective one and its efficacy was independent of concentration for concentrations higher than 1.0%. The same applied for concentrations higher than 1.5-2.0% for Agroaceite, Volck Miscible, and Sunspray Ultrafine, with high efficacies against eggs, protonymphs, and adults. PDSOs are highly effective against T. urticae, the use of these products should be encouraged in integrated citrus pest management programs in Spain. The next step will be to ascertain the efficacy under real field conditions.

Cover crops can serve as a reservoir of natural enemies by supplying alternative food sources as pollen. However, pollen quality and availability can modulate phytoseiid communities. In clementine trees associated with a cover crop of Festuca arundinacea ...