No abstract

The pathogenicity of Beauveria bassiana to one of the major pests of citrus crops, Phyllocoptruta oleivora, was assessed by inoculating mites with different concentrations of conidia (1 x 10(6), 5 x 10(6), 1 x 10(7), 5 x 10(7) and 1 x 10(8)). Treated mites were kept at controlled conditions (25 +/- 0.5 degrees C, 12 h photoperiod and 98% relative humidity) and mite survivorship was evaluated daily. Mortality was found to increase in time and was dependent on the conidia concentration, with values ranging from 24 to 91% for the lowest and highest conidia concentration, respectively. The calculated LC50 on the fifth day was 4.23 x 10(6) conidia/ml. Mean lethal time was 3.98, 9.79, 3.09 and 2.74 days for 5 x 10(6), 1 x 10(7), 5 x 10(7) and 1 x 10(8) conidia/ml, respectively. Conidia were found to adhere all over the mite body surface, especially at the anal region, where vegetative mycelium was found entering the mite body. We noticed the formation of small crystals inside the mite's body that were produced during colonization of the body cavity by the fungus. This is the first report of B. bassiana pathogenicity for this species.

O estudo da patogenicidade de Beauveria bassiana (Bals.) Vuill. ao ácaro Tetranychus urticae Koch foi desenvolvido a 25 ± 2°C, 70 ± 5% UR e 12 horas de fotofase, utilizando-se fêmeas recém-emergidas. Os ácaros foram mantidos durante seis dias em discos de folha de Canavalia ensiformis (L.) DC. inoculadas com B. bassiana, isolado 447, nas concentrações: 5x106, 1x107, 5x107, 1x108, 5x108 e 1x109 conídios/ml. Este isolado mostrou-se patogênico a T. urticae, apresentando aumento nos valores das mortalidades acumuladas (total, corrigida e confirmada) à medida que a suspensão de conídios se tornou mais concentrada. Nas seis concentrações testadas, os valores de mortalidade corrigida ao sexto dia, foram inferiores a 50%, sendo observada apenas na concentração de 1x109 conídios/ml, mortalidade total superior a 50%.

No abstract

The cassava green mite, Mononychellus tanajoa (Bondar), is an exotic pest in Africa and is the target of a classical biological control programme. Field data from the Neotropics, where it is indigenous, are presented for the first time, charting the variation in abundance of M. tanajoa over several seasons. This was highly variable, with a characteristic trough mid-year and a peak at the turn of the year. This pattern corresponded positively with rainfall levels, appearing to fit a phenology also characteristic of African studies, where rainfall at the start of the wet season promotes a leaf flush and so growth in M. tanajoa populations. Analyses implied some impact of leaf-inhabiting predatory mites (predominantly Neoseiulus idaeus Denmark & Muma) and a considerable impact of the fungal pathogen Neozygites floridana Fisher on M. tanajoa populations. This pathogen was not observed in the host population for several (generally dry) periods implying survival outside the host, perhaps as resting spores. This is a particularly desirable characteristic of a biological control agent. It is therefore proposed that N. floridana might be of particular use in drier cassava-growing areas where rainfall at the outset of the wet season is not sufficiently intense to cause heavy M. tanajoa mortality but may be sufficient to stimulate epizootics of the fungal pathogen, protecting the flush of new cassava growth.