Response of the predatory mite Phytoseiulus macropilis (Banks) to volatiles produced by strawberry plants in response to attack by Tetranychid mites (Acari: Phytoseiidae: Tetranychidae)

The attack of phytophagous mites may induce plants to produce volatiles, which in turn may attract predators. The occurrence of multiple phytophagous infestations on plants may influence predator response. In this paper, we investigated whether the attraction of the predatory mite Phytoseiulus macropilis (Banks) to phytophagous-infested plants would change with the simultaneous presence of two tetranichid mites Oligonychus ilicis (McGregor) and Tetranychus urticae Koch. While the former species is rarely found on strawberry plants and is only occasionally found in association with P. macropilis, the latter is commonly found on strawberry plants and is frequently found in association with P. macropilis. Y-tube olfactometer test assays demonstrated that the predator preferred plants infested with T. urticae, avoided plants infested with O. ilicis, and had no preference for plants infested with both phytophagous mite species. These results indicated that the presence of a non-prey species (O. ilicis) on a given plant can alter the response of the predator to one of its prey (T. urticae). The consequences of the predatory behavior determined in this study on the predator ability to control T. urticae population on strawberry plants are discussed.

Distribuição espacial de ácaros fitófagos (Acari: Tetranychidae) em morangueiro / Spatial distribution of phytophagous mites (Acari: Tetranychidae) on strawberry plants

O morangueiro, Fragaria x ananassa, pode ser atacado por diferentes espécies de ácaros fitófagos, dentre elas o ácaro-vermelho, Oligonychus ilicis McGregor, e o ácaro-rajado, Tetranychus urticae Kock. Essas espécies são encontradas juntas, alimentando-se, com maior freqüência, sobre a epiderme adaxial e abaxial das folhas, respectivamente. Neste trabalho estudou-se o padrão de escolha de O. ilicis e T. urticae por sítio de alimentação em plantas de morangueiro. Duas hipóteses foram formuladas: a primeira, que a escolha por sítios de alimentação estaria relacionada à aptidão das espécies; a segunda, que esta escolha seria determinada pela presença do heteroespecífico. Com o objetivo de testar tais hipóteses, avaliou-se a preferência, biologia e sucesso reprodutivo de O. ilicis e T. urticae sobre a face abaxial e adaxial de folhas de morangueiro infestadas ou não pelo heteroespecífico. O. ilicis preferiu permanecer sobre a face adaxial enquanto T. urticae preferiu permanecer sobre a face abaxial de folhas de morangueiro. A preferência pelas faces foliares correlacionou-se com o sucesso reprodutivo das espécies, avaliado pela taxa intrínseca de crescimento populacional (r m). O padrão de escolha não se alterou quando as espécies foram submetidas ao teste de escolha entre as faces foliares previamente infestadas pelo heteroespecífico. É discutida a possibilidade de T. urticae induzir defesas da planta capazes de reduzir a aptidão de O. ilicis e vice-versa. A possibilidade dessas espécies permanecerem juntas sobre plantas de morangueiro aumenta a capacidade de dano à cultura.

Many phytophagous mites can attack strawberry plants, Fragaria x ananassa, among them the southern red mite, Oligonychus ilicis McGregor, and the two-spotted spider mite, Tetranychus urticae Koch. They are found together feeding on the same plant on the upper and underside of the leaves, respectively. Here we studied the choice for feeding sites of O. ilicis and T. urticae on strawberry plants. The first hypothesis tested whether the feeding site choice would be related to the fitness of the species. The second hypothesis dealt whether the feeding site would be determined by the presence of a heterospecific mite. We evaluated the preference, biology and reproductive success of O. ilicis and T. urticae on the under and upper side surface of strawberry leaves infested or not by the heterospecific. O. ilicis preferred to stay on the upper side surface while T. urticae preferred the underside. The preference for the leaf surface correlated with the reproductive success of the species (measured by the intrinsic growth rate). The choice pattern of feeding sites did not alter when the choice test was applied using sites previously infested by heterospecific. Although O. ilicis and T. urticae, apparently, do not interact directly for feeding sites, there is a chance that the first species induces defenses in strawberry plant enabling to reduce the fitness of the second species. The possibility of those species stay together on strawberry plant increases the damage capacity to the culture.

Seletividade de extratos de nim (Azadirachta indica A. Juss.) ao ácaro predador Iphiseiodes zuluagai (Denmark & Muma) (Acari: Phytoseiidae) / Selectivity of neem extracts (Azadirachta indica A. Juss.) to the predatory Mite Iphiseiodes zuluagai (Denmark & Muma) (Acari: Phytoseiidae)

The relative toxicity of the leaf, seed and oil neem cake extracts of Azadirachta indica A. Juss (neem) to the predatory mite Iphiseiodes zuluagai (Denmark & Muma) (Acari: Phytoseiidae) was evaluated. To verify the relative toxicity of these extracts on the predatory mite, discriminatingconcentrations of the extracts were determined for adult females of the Oligonychus ilicis (McGregor) (Acari: Tetranychidae), through the method of concentration-mortality. Coffee leaf disks with 3.5 cm of the diameter were put floating on water and impregnated with dry residue of the extracts. Concentrations of neem extracts which caused mortality (99%) of O. ilicis, after 72h of exposition, were 277.4; 520.9 e 10.9 mg/ml for leaf, seed and oil neem cake, respectively. The discriminating concentration of extract ofoil neem cake for O. ilicis females was highly toxic to I. zuluagai; while extract of leaf and seed were selective to the predatory mite.

A toxicidade relativa dos extratos de folha, semente e óleo de torta de Azadirachta indica A. Juss (nim) ao ácaro predador Iphiseiodes zuluagai (Denmark & Muma) (Acari: Phytoseiidae) foi estudada em laboratório. Foram determinadas concentrações discriminatórias (CLs99) dos extratos de folha, semente e óleo de torta de nim para fêmeas adultas de Oligonychus ilicis (McGregor) (Acari:Tetranychidae), através de bioensaios de concentração-mortalidade. Arenas com 3,5 cm de diâmetro, confeccionadas com folhas de cafeeiro flutuando em água, foram impregnadas com resíduo seco dos extratos e usadas para se estimar a seletividade ao ácaro I. zuluagai. As concentrações dos extratos de nim que mataram 99% de O. ilicis, após 72h de exposição foram: 277,4; 520,9 e 10,9 mg/ml, para folha, semente e óleo de torta, respectivamente. A concentração discriminatória do extrato de óleo de torta de nim para fêmeas adultas de O. ilicis foi altamente tóxica ao ácaro I. zuluagai, as dos extratos de folha e de semente foram seletivos.