Infochemical use by predatory mites of the cassava green mite in a multitrophic context

Abstract

This thesis describes research on multitrophic interactions in a system consisting of (1) cassava plants ( Manihot esculenta ), (2) three herbivorous mites, i.e. the cassava green mite Mononychellus tanajoa, the red spider mite Oligonychus gossypii and the two-spotted spider mite Tetranychus urticae and (3) two exotic predatory mites Typhlodromalus manihoti and T. aripo , in Africa. The objectives are to understand how the two exotic predators (i) exploit chemical information to locate the target prey in pure and mixed odors conditions with the alternative prey mites, (ii) perform when feeding on different prey mite species and (iii) interact with each other.The predatory mites, T. manihoti and T. aripo were attracted to cassava leaves infested by M. tanajoa compared with non-infested leaves, when the predators were starved for 2, 6 or 10 hours. They were not attracted to 400 female M. tanajoa removed from infested plants nor to mechanically wounded leaves. In a choice situation, T. manihoti and T. aripo preferred odors from leaves infested by M. tanajoa to odors from leaves infested by O. gossypii regardless of the ratio M. tanajoa : O. gossypii . When M. tanajoa -infested leaves and T. urticae -infested leaves were offered in a choice situation, the response of the two predator species depended on the density of T. urticae . Typhlodromalus manihoti and T. aripo were attracted to odors from cassava leaves infested with both M. tanajoa and O. gossypii or to a mixture of odors from leaves infested with M. tanajoa and odors from leaves infested with O. gossypii, when compared to odors from non-infested leaves. In contrast, mixed odors from M. tanajoa -infested leaves and T. urticae -infested leaves did not yield a preference over odors from non-infested leaves.Typhlodromalus manihoti and T. aripo had a higher intrinsic rate of population increase (rm) and net reproduction (Ro), and a shorter generation time and doubling time on when they were feeding on M. tanajoa than on O. gossypii or T. urticae . Prey-related odor preference matched predator performance if the key prey is compared to the two inferior prey mite species.Typhlodromalus aripo displayed a marked preference for odors emitted from either infested cassava apices or infested young cassava leaves over infested old cassava leaves but showed equal preference for odors from apices and young leaves both infested with M. tanajoa . Typhlodromalus manihoti did not discriminate between volatiles from the three infested cassava plant parts. This mirrors the differential distribution of the two predators on cassava plant foliage.Carnivorous arthropods when searching for adequate food and habitat for themselves and their progeny should in the meantime avoid becoming food for other organisms. Intraguild interactions have been investigated for the predatory mite species T. manihoti , T. aripo and the native species Euseius fustis . Typhlodromalus manihoti is able to discriminate between odors from patches with con- and heterospecific competitors and prefers to visit patches with heterospecifics. Typhlodromalus aripo preferred to move away from patches with heterospecifics or conspecifics. Euseius fustis avoided odors from patches with conspecifics as well as odors from patches with the heterospecifics T. manihoti and T. aripo .In conclusion, this thesis shows that the distribution and diversity of prey species, intraguild predation and competition are likely to play an important role in infochemical use by T. manihoti and T. aripo . In addition to predator-prey interactions, interactions between predators can also be considered as important factors affecting population dynamics of both prey and predators.</p