Influence of abiotic factors on diapause termination and temperature requirements for postdiapause development in the European red mite, Panonychus ulmi (Acari: Tetranychidae).

The European red mite Panonychus ulmi (Koch) is widely distributed and it can severely affect pome fruit crops, particularly apple. Pest outbreaks are related to an overuse of non-selective pesticide treatments that lead to the development of resistance and the absence of natural enemies in the orchard. A key aspect to optimize the use of pesticide treatments in the context of IPM is to increase the knowledge on the biology and ecology of the pest to better predict population dynamics and outbreaks. For the European red mite, knowledge on the conditions that lead to diapause breaking by winter eggs is essential to model population dynamics. To increase this knowledge, winter eggs were collected during field surveys in northen Spain during three years and egg hatching was monitored under controlled temperature and photoperiod conditions in the laboratory. The "number of days exposed to cold temperatures" was the most significant factor that positively affected hatching of overwintering eggs. The time required for 50% of the egg population to hatch (T50%) was also negatively modulated by the duration of exposure to cold temperature. The temperature threshold for postdiapause eggs development collected from the field was estimated between 5 and 6 ºC in 2005 and 2007, respectively. Moreover, the degree-days required for post diapause development were estimated between 263.2 and 270.3, depending on the year of collection. Collectively, we provide additional information on the diapause termination and postdiapause development of the European red mite that may effectively contribute to optimize pest population models.

Compatibility of the entomopathogenic fungus Beauveria bassiana with flufenoxuron and azadirachtin against Tetranychus urticae.

Laboratory studies were developed to evaluate the compatibility of flufenoxuron and azadirachtin with Beauveria bassiana against Tetranychus urticae larvae along with the required Probit analysis of the involved chemicals on all of the life stages of this mite. Flufenoxuron displayed parallel regression lines for the mortality of eggs, deutonymphs and adults. Larvae and protonymphs were the most susceptible life stages. Protonymphs were 35 times more sensitive than eggs and adults. Azadirachtin gave equal mortality on proto- and deutonymphs. The response of eggs and adults was equivalent when treated with azadirachtin. The regression lines for proto- and deutonymphs were parallel to those of adults and eggs yet three times more sensitive. The effects of separate combinations of the entomopathogenic fungus Beauveria bassiana at its LC(20) with flufenoxuron and azadirachtin at their corresponding LC(40) were evaluated on mite larvae. The application of flufenoxuron with B. bassiana revealed a clear synergy. While the combination of azadirachtin and B. bassiana had an additive effect. These combinations with B. bassiana could improve mite control by contributing to a decline in the likelihood of resistance so often described in the literature.

Laboratory rearing and life history of an emerging grape pest, Xylotrechus arvicola (Coleoptera: Cerambycidae).

Several aspects of the biology of Xylotrechus arvicola (Olivier), an emerging grape pest, were studied under laboratory conditions. Four diets were tested to rear this species in the laboratory. Among them, only one made rearing from larva to adult possible. The highest mortality, in all cases, was recorded during the first days of larval development. Larvae were kept 45 days at 8°C to break diapause in order to reduce the normal field larval developmental time. The species' developmental time was similar between sexes, while pupal developmental time and weight were significantly greater for females than for males. As part of a complementary study, life table parameters of females obtained from the larvae reared on the artificial diet were compared to those of females emerged from field-infested grape root wood. Both laid the majority of eggs in the first two weeks after emergence, and they had a similar pre-laying period. Nevertheless, the females from the diet-reared larvae lived significantly longer, laid eggs over a longer period of time and showed higher fertility than those emerging from infested grape root, suggesting that diet fulfils larval nutritional needs. The species' laboratory-reared population exhibited a low intrinsic growth rate value (rm=0.01) as a result of its long egg-to-adult developmental time and its high larval mortality.

Effects of variable and constant temperatures on the embryonic development and survival of a new grape pest, Xylotrechus arvicola (Coleoptera: Cerambycidae).

Xylotrechus arvicola Olivier (Coleoptera: Cerambycidae) has become a new expanding pest in grape (Vitis spp.) crops. To better improve control tactics, the consequences of 11 constant (12, 15, 18, 21, 24, 27, 30, 32, 34, 35 and 36°C) and nine variable temperatures (with equal mean temperatures at each of the nine constant rates ranging from 15 to 35°C) on survival and embryonic development were studied. The eggs were able to complete development at constant temperatures between 15 and 35°C, with mortality rates at the extremes of the range of two and 81.5%, respectively. Using variable temperatures a mortality rate of 38.9% at a mean temperature of 15°C and 99% at 35°C was observed. The range of time for embryonic development was 29.5 d at 15°C to 6 d at 32°C at constant temperatures, and from 29.6 d at 15°C to 7.2 d at 32°C at variable temperatures. The goodness-of-fit of different development models was evaluated for the relationship between the development rate and temperature. The models that gave the best fit were the Logan type III for constant temperatures and the Brière for variable temperatures. Optimum temperatures were estimated to be from 31.7 to 32.9°C. The models that best described embryo development under natural field conditions were the Logan type III model for constant temperatures (98.7% adjustment) and the Lactin model for variable temperatures (99.2% adjustment). Nonlinear models predicted faster development at constant temperatures and slower development at variable ones when compared with real field development, whereas the linear model always predicted faster development than what actually took place.

Effects of lufenuron on Lobesia botrana (Lepidoptera: Tortricidae) egg, larval, and adult stages.

The effect of the chitin synthesis inhibitor lufenuron was evaluated against different developmental stages of Lobesia botrana Den. & Schiff. (Lepidoptera: Tortricidae). Lufenuron fed to adults at 10 ppm reduced their fecundity and fertility, but it did not affect adult longevity. High activity was observed against L. botrana eggs with greater effect on 1-d-old eggs than on the other age classes and on eggs treated by direct contact rather than those laid on a previously treated surface. Eggs laid by treated adults showed the same effects during development as eggs treated by contact or those laid on a treated surface. Larvae that emerged from treated eggs could not perforate grape berries. Administered into the diet, lufenuron had a larvicidal effect, resulting in similar LC50 values for different instars: 0.07 ppm for first instars, 0.08 ppm for third instars, and 0.11 ppm for fifth instars. None of the larvae treated with sublethal concentrations throughout their life emerged as adults at the highest concentration (0.08 ppm), and only 70% emerged at the lowest concentration (0.0025 ppm).

Effects of triflumuron on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranichydae).

The effects of triflumuron on the mortality, fecundity, and fertility of the two-spotted spider mite, Tetranychus urticae, were evaluated in the laboratory. No differences in toxicity for larvae, protonymphs and deutonymphs were observed, but immature stages were 3.8-times more susceptible than adults at the LC50. The compound exhibited a direct contact ovicidal activity influenced by eggs age. 48-72 h old eggs were significantly more sensitive than eggs of the other age classes. No hatch inhibition was observed in eggs laid by treated adult females using a sublethal dose at two physiological times (<12 and 48-72 h old). However. fecundity decreased in younger treated females, but it increased in the older-ones. The toxicity for immatures and eggs, and the sublethal effects described suggest that triflumuron could be an interesting incorporation in integrated pest programs of T. urticae.