Biological control of twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), using Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseidae) on impatiens

The effectiveness of the predatory mite, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae), as a suppressive agent of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), was evaluated on impatiens plants at predator:prey release ratios of 1:3 (high), 1:15 (medium) and 1:30 (low). Releases at each ratio were made at low and high initial T. urticae densities to determine if initial pest population size influenced the suppressive ability of the predator. After only one week, P. persimilis was reduced both the higher and lower T. urticae populations to negligible levels and kept damage to 5% or less, but only at the 1:3 ratio. At the medium predator:prey ratio, predators prevented spider mite numbers and damage from increasing, but did not reduce either. At the lowest ratio (1:30) spider mite populations and plant damage continued to increase. Both the medium and low ratios allowed unacceptably high levels of plant damage. A regression model indicated that a release ratio of 1:10 or higher should consistently reduce the pest population and associated damage to acceptable levels. However, if spider mites establish at high levels of infestation similar to those we tested experimentally, even releasing predators at a 1:3 ratio will not provide certain control. To reliably control damage from spider mites on impatiens, predators must be released as soon as spider mites are detected in order to reduce spider mite populations to non-detectable levels within one or two weeks of predator release

Maternal effects shape dynamic trajectories of reproductive allocation in the ladybird<i>Coleomegilla maculata</i>

AbstractWe followed lifetime trajectories of reproductive allocation inColeomegilla maculatafemales of three different size classes produced by rearing beetles on three different daily larval feeding regimes (30 min, 6 h orad libitumaccess to eggs ofEphestia kuehniella). We hypothesized that small females would produce fewer and smaller eggs than larger females and that reproductive effort would decline with female age. Females were mated with a male from the same treatment and then isolated withad libitumfood for their entire adult lives. Egg size increased over time in all treatments; small females started off laying the smallest eggs, but increased egg size more rapidly than larger females, until all treatments converged on a similar egg size around the 20th day of oviposition. Large females realized a larger proportion of their fecundity early in life, but smaller females increased daily fecundity over time. Reproductive effort (egg mass/body mass) did not decline over 30 oviposition days; it remained constant in large females, but increased among small and medium females, suggesting gradual compensation for larval food deprivation. An increase in egg size with maternal age may be an adaptive strategy to maximize fitness on ephemeral patches of aphid prey, assuming females reproduce in a single aphid outbreak and that offspring produced later in the aphid cycle experience greater competition and risk of mortality compared to those produced earlier. We demonstrate for the first time in Coleoptera that dynamic changes in both egg size and number occur as a function of female age and illustrate that such changes are constrained by larval feeding histories via their effects on maternal body size.</jats:p

Variação sazonal das condições internas de colônias de Melipona marginata obscurior Moure, no Rio Grande do Sul, Brasil Seasonal variations in the internal condictions of colonies the Melipona marginata obscurior Moure, at Rio Grande do Sul, Brazil

O conhecimento das condições internas das colônias de Melipona marginata obscurior Moure, 1971, ao longo do ano, é importante para a compreensão do comportamento das abelhas sem ferrão e seu manejo. Visa-se o estudo da biologia de M. marginata obscurior em ambiente natural, com ênfase na variação sazonal das condições internas das colônias. Quatro colônias foram estudadas no Centro de Pesquisas e Conservação da Natureza Pró-Mata, em São Francisco de Paula, RS. Avaliou-se o volume dos ninhos, a ocorrência e duração da diapausa e o número total de favos e de células de cria nos dois últimos favos. O volume do invólucro inicial das quatro colônias foi semelhante, variando de 2,26 a 2,69 litros. Ao final da avaliação observou-se que o volume do invólucro da colônia A reduziu 5%, enquanto as demais cresceram 61% (colônia B), 84% (C) e 71% (D). A partir do monitoramento mensal dos favos de cria constatou-se a ocorrência de diapausa em três colônias (B, C e D) enquanto a colônia A permaneceu com postura ininterruptamente. As colônias cessaram a construção de células de cria e postura da rainha durante o outono e reiniciaram esta atividade no final do inverno. Sugere-se que a variação do período de diapausa (8 a 23 semanas) seja determinada por fatores internos das colônias. O número máximo de favos registrado durante a primavera e o verão variou de 6 a 8, enquanto que o número estimado de células de cria dos dois últimos favos variou de 116 a 1190. Foi possível reconhecer padrões, bem como variações sazonais, relacionados ao volume do invólucro dos ninhos, à ocorrência de diapausa e ao número de favos e de células de cria nos dois últimos favos. Variações sazonais das condições internas entre as colônias mostraram-se evidentes e podem ser creditadas a características intrínsecas das colônias.<br>The knowledge of the internal conditions of Melipona marginata obscurior Moure, 1971 colonies, through the year, is important for the understanding of the behavior and handling of the stingless bees. This work aims the biological study of the M. marginata obscurior in its natural environment, whith emphasis on the seasonal variation of the internal conditions of colonies. Four colonies were studied at Centro de Pesquisas e Conservação da Natureza Pró-Mata, in São Francisco de Paula, Rio Grande do Sul. It was valuated the nest volume, the diapause occurrence and duration, and the total number of combs and brood cells in the two last combs. For the four colonies the initial involucrum volume was similar, varying from 2.26 to 2.69 liter. In the final of the valuation, it was observed that the colony A volume was reduced to 5%, while the others grow up 61% (colony B), 84% (C) e 71% (D). From the monthly monitoring of the brood combs it was shown that diapause occurred in three colonies (B, C e D), while the colony A remained ininterruptly with posture. The colonies ceased the construction of brood cells and posture of the queen during the autumn and restarted this activity on the final of the winter. It's suggested that diapause period variation (8 to 23 weeks) is determined by internal factors of the colonies. The maximal number of combs, registered during the spring and the summer, varied from 6 to 8, while the number of the brood cells of the two last combs varied from 116 to 1190 cells. It was possible to recognize patterns, as well seasonal variations related to involucrum volume of the nest covering, to diapause occurrence and to number of the combs and brood cells on the two last combs. The seasonal variations of the internal conditions among the colonies were obvious and can be credited to intrinsic characteristics of the colonies