Toxicities of acetogenin-based bioacaricides against two-spotted spider mite and selectivity to its phytoseiid predators.

Tetranychus urticae is the main pest of strawberry crops and can cause up to 80% of productivity losses under high infestations. Aiming to search T. urticae management alternatives compatible with eco-friendly or organic-based food production systems, this study evaluated the lethal and sublethal toxicities of formulated derivatives from Annonaceae (rich in acetogenins) against this pest species. In addition, it also evaluated the selectivity of the most promising formulation to the predatory mites Neoseiulus californicus and Phytoseiulus macropilis, which are largely applied in biological control in Brazil. Among the derivatives tested, the emulsion from the ethanolic seed extract of Annona mucosa-ESEAm (major component: acetogenin bis-tetrahydrofuran rolliniastatin-1) caused pronounced mortality of T. urticae after 120 h of exposure (LC50 = 465.5 mg L-1), in a comparable or superior manner to an abamectin-based synthetic acaricide used as positive control (LC50 = 1243.4 mg L-1). Moreover, ESEAm exposure resulted in a significant decrease in the number of eggs laid by females and caused the most pronounced ovicidal action for T. urticae, with only 5% embryonic viability. However, ESEAm also showed high toxicity to the predatory mites tested, causing 100% mortality for both species after 120 h exposure, similar to abamectin. The interaction between these bioacaricides and biological control agents should be tested under field conditions to further assess the potential ecological selectivity of these derivatives.

Antipredator behaviours of a spider mite in response to cues of dangerous and harmless predators.

Prey are known to invest in costly antipredator behaviour when perceiving cues of dangerous, but not of relatively harmless predators. Whereas most studies investigate one type of antipredator behaviour, we studied several types (changes in oviposition, in escape and avoidance behaviour) in the spider mite Tetranychus evansi in response to cues from two predatory mites. The predator Phytoseiulus longipes is considered a dangerous predator for T. evansi, whereas Phytoseiulus macropilis has a low predation rate on this prey, thus is a much less dangerous predator. Spider mite females oviposited less on leaf disc halves with predator cues than on clean disc halves, independent of the predator species. On entire leaf discs, they laid fewer eggs in the presence of cues of the dangerous predator than on clean discs, but not in the presence of cues of the harmless predator. Furthermore, the spider mites escaped more often from discs with cues of the dangerous predator than from discs without predator cues, but they did not escape more from discs with cues of the harmless predator. The spider mites did not avoid plants with conspecifics and predators. We conclude that the spider mites displayed several different antipredator responses to the same predator species, and that some of these antipredator responses were stronger with cues of dangerous predators than with cues of harmless predators.

Physicochemical and nutritional alterations induced by two-spotted spider mite infestation on strawberry plants

Background Strawberry is a pseudofruit mainly cultivated in temperate climate regions. Considering its high levels of ascorbic acid and phenolic compounds, the consumption of strawberry fruit can be beneficial to health. The Brazilian strawberry production revolves around 3000 tons per year, significantly influencing the food market and generating income to farmers. However, this production can be partially impaired by two-spotted spider mite (TSSM) Tetranychus urticae Koch infestations, due to decreases in the quality and quantity of fruit. Since there are no data in the literature about alterations caused by TSSM infestation in strawberry plants, our work aimed towards evaluating nutritional and physicochemical parameters of TSSM-infested strawberry plants, along with the related chemical treatment (CT) (acaricide) or biological treatment (predatory mite Phytoseiulus macropilis Banks). Results Strawberry fruit from TSSM-infested plants present the highest levels of acidity and exhibit low levels of anthocyanin and phenolic compounds, while fruit from TSSM-infested plants + biological control using predatory mite shows high levels of soluble solids, phenolic compounds and ascorbic acid, along with a high soluble solid content/titratable (SSC/TA) acidity ratio, which indicates high quality fruit. Conclusions Our results suggest that TSSM infestation decreases fruit quality and that the biological control of TSSM using a predatory mite is a suitable alternative to organic production, since the presence of predatory mite does not affect fruit quality and development.

Ácaros predadores (Acari) associados à cultura do morango (Fragaria sp., Rosaceae) e plantas próximas no Estado do Rio Grande do Sul / Predatory mites (Acari) associated with strawberry and neighboring plants in the State of Rio Grande do Sul

O objetivo deste estudo foi determinar as espécies de ácaros predadores associados à cultura do morango e em plantas associadas, no estado do Rio Grande do Sul. Este estudo foi conduzido nos municípios de Bom Princípio, Capitão e Lajeado em plantações de morango da variedade Oso Grande em túnel baixo. As avaliações foram feitas mensalmente entre agosto de 2002 e março de 2004. Nas plantas de morango, as amostras foram constituídas de três folhas coletadas em cada uma das 15 plantas escolhidas ao acaso, totalizando 45 folhas/campo. Nas plantas associadas, o esforço de amostragem foi de uma hora para cada planta avaliada. Ácaros das famílias Ascidae, Parasitidae, Phytoseiidae, Cunaxidae, Erythraeidae, Stigmaeidae e Tydeidae foram observados associados com o ácaro rajado, Tetranychus urticae Koch, 1836, praga importante na região onde este estudo foi conduzido. Vinte espécies foram identificadas, 14 das quais pertencem à família Phytoseiidae. Phytoseiulus macropilis (Banks, 1905) e Neoseiulus californicus (McGregor, 1954) foram as espécies mais comuns. Nas plantas asssociadas, a maior diversidade foi observada em Richardia sp. (seis espécies), Agerantum conyzoides L.(quatro espécies) e Sonchus oleraceus L., Bidens pilosa L.e Rumex sp. (três espécies). Uma chave docotômica é apresentada para a identificação das espécies.

The aim of this study was to determine the species predatory mites on strawberry crop and associated plants in the State of Rio Grande do Sul. It was conducted in Bom Princípio, Capitão and Lajeado counties, in crops of strawberry Oso Grande variety in low tunnels. The evaluations were done monthly between August 2002 and March 2004. In the plants of strawberry, the samples were constituted of three leaves collected in each of 15 plants taken randomly, totaling 45 leaves/field. In the associated plants, the sampling effort was of one hour for each plant evaluated. Mites of the families Ascidae, Parasitidae, Phytoseiidae, Cunaxidae, Erythraeidae, Stigmaeidae and Tydeidae were observed associated with the two-spotted spider mite, Tetranychus urticae Koch, 1836, important pest of this crop in the region where the study was conducted. Twenty species were identified, 14 of which belong to the family Phytoseiidae. Phytoseiulus macropilis (Banks, 1905) and Neoseiulus californicus (McGregor, 1954) were the most common species. On associated plants, the highest diversity of predatory mites was found on Richardia sp. (six mite species), Agerantum conyzoides L. (four mite species) and Sonchus oleraceus L., Bidens pilosa L. and Rumex sp. (three mite species). A dichotomous key is presented for the separation of the species collected.