Neotropical Entomology 34(6): 991-998 (2005) Resistência de PALAVRAS-CHAVE: Ácaro rajado, manejo da resistência, controle químico ABSTRACT -Studies on artificial laboratory selections with abamectin, cross-resistance relationships, and stability of resistance were carried out with Tetranychus urticae Koch to provide basic information for an abamectin resistance management program. Selections for resistance and susceptibility to abamectin were performed in a population of T. urticae, collected from a commercial strawberry field in the State of São Paulo, Brazil. After five selections for resistance and five selections for susceptibility, susceptible (S) and resistant (R) strains of T. urticae to abamectin were obtained. The resistance ratio (R/S) at the LC 50 reached 342-fold values. The toxicity of eight acaricides was evaluated in the R and S strains, observing significant differences (at LC 50 ) between R and S strains for milbemectin, fenpropathrin and chlorfenapyr. Significant correlation was detected between the LC 50 s of abamectin and milbemectin, indicating cross-resistance between these acaricides. No crossresistance was detected for the acaricides fenpyroximate, cyhexatin, propargite and dimethoate. The stability of abamectin resistance was also studied under laboratory conditions. Abamectin resistance was unstable in the absence of selection pressure. For all studied populations (with 75, 50 and 25% of initial frequency of resistant mites), the percentage of resistant mites decreased to levels equal or lower than 15% in six months. The results indicate that milbemectin should be avoided for managing abamectin resistance in T. urticae.

The two-spotted spider mite, Tetranychus urticae Koch (green-form) (Acari: Tetranychidae), is a worldwide pest of many plant species, including several agricultural crops (Flechtmann, 1985; Tomczyk and Kropczyńska, 1985). This tetranychid mite is one of the most important pests of strawberry (Chiavegato and Mischan, 1981) and causes significant damage to various other crops, such as apple, peach, papaya, kidney bean, cotton and ornamental plants in Brazil (Flechtmann, 1985). The ability of T. urticae to develop resistance to several acaricides has caused problems in many countries involved in agricultural production during the past 40 years (

This work was carried out in orchards of guava progenies, and loquat and peach cultivars, in Monte Alegre do Sul, SP, Brazil, in 2002 and. Guavas and loquats were bagged and unbagged bi-weekly and weekly, respectively, for assessment of the infestation period. Peach was only bagged weekly. The assays started when the fruits were at the beginning of development, but still green. Ripe fruits were taken to the laboratory and placed individually into plastic cups. McPhail plastic traps containing torula yeast were hung from January 2002 to January 2004 to assess the fruit fly population in each orchard, but only the Ceratitis capitata population is here discussed. Five tephritid species were reared from the fruits: Anastrepha bistrigata Bezzi, A. fraterculus (Wiedemann), A. obliqua (Macquart), A. sororcula Zucchi, and C. capitata, in addition to six lonchaeid species: Neosilba certa (Walker), N. glaberrima (Wiedemann), N. pendula (Bezzi), N. zadolicha McAlpine and Steyskal, Neosilba sp. 4, and Neosilba sp. 10 (both species are in the process of being described by P. C. Strikis), as well as some unidentified Neosilba species. Ten parasitoid species were obtained from fruit fly puparia, of which five were braconids: Asobara anastrephae (Muesebeck), Doryctobracon areolatus (Szépligeti), D. brasiliensis (Szépligeti), Opius bellus Gahan, and Utetes anastrephae (Viereck), and five figitids: Aganaspis pelleranoi (Brèthes), Dicerataspis grenadensis Ashmead, Lopheucoila anastrephae (Rhower), Leptopilina boulardi (Barbotin, Carlton and Kelner-Pillaut), and Trybliographa infuscata Diaz, Gallardo and Uchôa. Ceratitis capitata showed a seasonal behavior with population density peaking at the second semester of each year. Anastrepha and Neosilba species remained in the orchards throughout both years.

This work aimed to evaluate the differential toxicity of pesticides to populations of the mite species Neoseiulus californicus (McGregor) and Tetranychus urticae Koch collected from commercial crops of strawberry (Fragaria sp.) in Atibaia county, State of São Paulo, Brazil. In the test of acute toxicity of pesticides, adult females of N. californicus received the pesticide treatment under Potter spray tower. The predaceous mite N. californicus showed the same or higher tolerance than T. urticae to various pesticides in laboratory. The highest difference was observed to the acaricide propargite, for which the predaceous mite was 25.1 times more tolerant than the two-spotted spider mite. This phytoseiid was also 4.7, 2.9 and 2.5 times more tolerant than T. urticae to chlorfenapyr, fenpyroximate, and cyhexatin, respectively. In the test of residual toxicity of pesticides, the chemicals were sprayed on plants of strawberry in the field. Leaves were collected after different periods from the treatment and artificially infested with adult females of N. californicus. The mortality was assessed 48h or 72h after treatment. Fenpyroximate, fenpropathrin, dimethoate, propargite, sulphur, and benomyl were innocuous to N. californicus. Chlorfenapyr, cyhexatin, and abamectin were significantly harmful to the predaceous mite causing initial mortality rates between 37.5% and 57.5%. The use of predaceous mites like of this population of N. californicus, which presents low susceptibility to various pesticides can be very useful for programs of management of T. urticae on strawberry in Brazil.

The purpose of this study was to evaluate the performance of Neoseiulus californicus (McGregor) for the control of Tetranychus urticae Koch in commercial strawberry fields, under greenhouse conditions, in association or not with the use of acaricides. The N. californicus strain used in this study was tolerant or resistant to several pesticides. Three experiments were carried out in the State of São Paulo, Brazil. For the first experiment, the initial infestation of T. urticae was 87.1 active stages per leaflet. Two applications of propargite were made on the first and the 14th day of the experiment. Approximately 2 h after each propargite application, N. californicus was released at a rate of 3.0 and 1.9 adult mites per plant, respectively, for each application. The population of T. urticae decreased from 87.1 to 2.8 mites per leaflet in the first three weeks. After this period, the population of T. urticae was maintained at low levels (

Neotropical Entomology 34(5): 815-822 (2005) Efeito de Isca Tóxica à Base de Spinosad Contra Ceratitis capitata (Wied.) PALAVRAS-CHAVE: Insecta, mosca-das-frutas, inseticida, mortalidadeABSTRACT -Laboratory studies were conducted to determine the mortalities caused by spinosad in Ceratitis capitata (Wied.) and Anastrepha fraterculus (Wied.). Spinosad formulated bait, diluted in water, was compared with baits of malathion, trichlorfon, fenthion and deltamethrin. The lethal time increased for C. capitata (medfly) adults fed in lower concentrations of spinosad. The LT50 values for C. capitata were estimated in 106, 126 and 154 min for 80, 8 and 4 ppm, respectively. No differences at LT50 were observed for different ages, 2-3d, 3-5d and 5-7d old C. capitata exposed to 80 ppm. Both fruit fly species presented similar pattern of survival when treated with spinosad at 80 ppm. In general, fenthion and trichlorfon showed LT50 values lower than spinosad for different ages of medfly. After 180 min from initial exposure to spinosad bait, the mortality rates of 2-3d and 3-5d old C. capitata were similar to that by fenthion. The LT50 for A. fraterculus was estimated in 85.9 min, slightly shorter than for C. capitata when both species were exposed to 8 ppm of spinosad. Medfly adults exposed to concentrations equal or inferior to 0.4 ppm of spinosad showed LT50s longer than 12 h. Leaves treated and kept in the field with baits of spinosad, malathion, fenthion and deltamethrin, caused high mortalities of medfly adults until two days after treatment.

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