Trichoribates trimaculatus, (Koch)

Desurmont, Gaylord A., Kerdellant, Elven, Pfingstl, Tobias, Auger, Phillipe, Tixier, Marie-Stéphane & Kreiter, Serge, 2019, Mites associated with egg masses of the viburnum leaf beetle Pyrrhalta viburni (Paykull) on Viburnum tinus L., Acarologia 59 (1), pp. 57-72 : 66

Impact of T. trimaculatus on overwintering success of P. viburni eggs

The infestation of V. tinus twigs by P. viburni inside cages in August 2017 was highly successful. A total number of 463 egg masses were laid on the 54 twigs selected for the study: the 26 twigs selected for the mite treatment contained in average 9.4 ± 1.0 egg masses / twig, and the 28 twigs selected for the control treatment contained in average 7.8 ± 0.9 egg masses / twig. On October 10 2017, five weeks after the addition of 20 T. trimaculatus inside the sleeve nets, the five twigs from the mite treatment that were cut and inspected for mite presence contained an average of 7.6 ± 3.4 T. trimaculatus individuals, showing that some mites had successfully established inside the nets. At the end of the experiment in April 2018, both adult and immature nymphs of T. trimaculatus were found inside the sleeve nets, indicating that the mites had produced a new generation. Some of the mites were found on the netting material (anecdotal observation), but most of them were found on the twigs, inside the egg mass cavities. An average of 5.3 ± 1.2 live T. trimaculatus individuals (adults + nymphs) per twig was found in twigs from the mite treatment, and an average of 1.3 ± 0.6 individuals was found in twigs from the control treatment. This difference was highly significant (χ² = 13.9, P <0.001). Egg hatch of P. viburni occurred in the petri dishes between mid-March and early April 2018. The mean number of larvae that emerged per egg mass was 2.8 ± 0.3 for twigs from the mite treatment (N = 21) and 2.9 ± 0.5 for twigs from the control treatment (N = 23). Considering that there is an average of 8 eggs per egg mass ( Weston et al. 2008), these numbers represent 35% and 36% of egg survivorship, respectively. The variables included in the model explained a significant amount of variation in larval emergence (full model: F 10,31 = 3.1, P <0.01, R² = 0.34), but neither the presence of mites inside sleeve nets (F 1,31 = 0.6 P = 0.5), the number of egg masses on twigs (F 1,31 = 0.1, P = 0.7), nor the interaction between these two terms (F 1,31 = 0.4 P = 0.5) had an effect on larval emergence per egg mass. In other words, the presence of mites did not impact P. viburni egg overwintering success. Shrub was the only factor that had a significant effect on larval emergence (F 7,31 = 4.3, P <0.01), indicating a plant-related effect on egg survivorship. This effect could have been twig wounding response, which was not measured during this experiment. These results remained consistent after excluding the twigs from the control treatment that contained live mites at the end of the experiment (7 twigs out of 23) and twigs from the mite treatment that did not contain any live mites at the end of the experiment (3 twigs out of 21).