Contribución al manejo integrado de ácaros tetraníquidos (Acari: Tetranychidae) que afectan a frutales de clima templado

Abstract

Tetranychus urticae is a cosmopolitan and polyphagous spider mite pest that causes problems in more than 150 economically important crops. This species is a key pest in many of these hosts. On the other hand, Panonychus ulmi is also a widespread and polyphagous species important as pest of fruit trees and, specially, of the apple tree. The importance of spider mites as pests species have recently increased. The massive use of no selective pesticides has been one of the reasons, because these compounds have dramatically reduced the populations of its natural enemies. This fact, combined with the development of resistances against many acaricides, is the reason why the spider mites are currently one of the most important phytosanitary problems. Taking into account the importance to implement Integrated Pest Management (IPM) programs, developing researches to optimize its implementation in the case of spider mite pest has a special interest. In regard with T. urticae, the effect of two biorational pesticides (the inhibitor of chitin synthesis, flufenoxuron, and the ecdysone antagonist, azadirachtin) has been deeply analysed in this work. On the other hand, the compatibility of both compounds and the entomopathogenic fungus Beauveria bassiana has also been researched. Flufenoxuron showed an important acaricidal effect on eggs, protonymphs, deutonymphs and adults of T. urticae, being especially effective on protonymphs. Meanwhile, azadirachtin also showed an interesting effect on the same spider mite developmental stages (more important on protonymphs and deutonymphs), although lower than in the case of flufenoxuron. When both acaricides were applied on adult females of the pest, the effect was different; flufenoxuron did not affect to the longevity and fecundity, but it has a negative effect on fertility and on the percentage of the progeny survival; on the contrary, azadirachtin only affected the female longevity and fecundity. To know the effect that the pesticides have on the life table parameters of the pest populations, at specific physical conditions, is very interesting in IPM programs. The current work shows that, under the bioassay conditions, flufenoxuron significantly reduced the intrinsic rate of increase (rm) of T. urticae at 2 mg/l. Therefore, at this concentration, mite population increases extremely slowly, with a doubling time (DT) of more than 2,200 days. Similarly, azadirachtin caused a dramatic reduction of the rm when applied at the concentration of 80 mg/l. In fact, the value of the rm was negative, indicating that the treated population tended to disappear (halving every 21 days). Researches about the joint use of pesticides and natural enemies have an obvious relevance in IPM programs. In this study, it was shown that flufenoxuron did not affect the mycelial growth of B. bassiana and, when used with the entomopathogenic fungus on T. urticae larvae, a synergistic effect was observed. Meanwhile, although azadirachtin did reduce the growth of the mycelium of the fungus, when applied together on the mite, a synergistic effect was also observed, although less pronounced than in the case of flufenoxuron. In regard with P. ulmi, the researches were, first, focused on improving their laboratory mass rearing. Secondly, the possibility to obtain individuals from the field was analysed. Finally, the determination of the end of diapause and the modellization of the embryonic development, to predict the hatching date of the P. ulmi eggs in the field, was also researched. The fitness of 12 plant species as P. ulmi hosts was evaluated. The host used to feed the spider mite significantly influenced on biological and life table parameters of the females. So, important differences between hosts were observed with respect to female longevity and fecundity, (fertility, however, was not affected). Hosts also influenced the developmental time and survival of the immature stages of the mite. The higher value of rm was obtained on apple tree, while a dramatically decreasing was observed in rose, cherry and chaenomeles (with positive values close to zero), becoming negative in the case of pear tree. On this host, and under the conditions of the bioassay, the spider mite population tends to disappear over time. Researches to improve the establishment of laboratory colonies of P. ulmi from field overwintering eggs were developed. The factors "temperature" and "period keeping cold" applied in laboratory to collected eggs did not affect the percentage of hatching when the collection was late. On the contrary, when the collection is earlier, both factors had influence on this parameter. The "period keeping cold" is the factor that affects more significantly on the percentage of hatching finally achieved. This percentage is higher as the number of cold days increases (reaching 60% for 100 days, compared to 10% for 10). Moreover, this factor (in the case of eggs collected at early date) is the only one that affects to the required time to get the 50% of egg hatching (T50%). In fact, the T50% value decreases as the number of days in cold increases (T50% reaches a value of about 15 days when the eggs were in cold 100 days and about 40- 50, when they were in cold 10 days). Finally, the date to which the beginning of the postdiapausa of field overwintering P. ulmi eggs happened was estimated (18 and 20 February in 2005 and 2007, respectively). The Lower Developmental Thresholds (LDT) and the Degree Days values (DD) in the same years (5.47 ° C and 6.13 ° C, respectively, for LDT and 55.3 and 276.4, respectively, for DD) were also obtained. These data could become in a valuable tool for decision making in the integrated management of the spider mite.