Geotaxis and leaf-surface preferences mitigate negative effects of a predatory mite on an herbivorous mite

Abstract

Reproductive success and population growth of an herbivorous mite are limited by activities of phytoseiid predators. However, occurrences on upper versus lower leaf surfaces are sometimes mismatched between these prey and predators. The mismatch potentially mitigates predation risk for the prey species. We assessed factors that affect mite distributions on leaf surfaces, testing whether the presence of the phytoseiid mite Phytoseius nipponicus alters the leaf-surface distribution and reproductive success of the herbivorous false spider mite Brevipalpus obovatus. The host plant was Viburnum erosum var. punctatum (Adoxaceae). Leaves were set in natural (TRUE) and reversed (upside down; INVERTED) orientations using experimental devices. Both surfaces were accessible to mites. We detected lower and abaxial leaf-surface preferences in P. nipponicus. In contrast, upper and adaxial surfaces were preferred by B. obovatus. Thus, prey and predatory mites accumulated on different sides of leaves. Presence of the predator also indirectly decreased egg production in B. obovatus. Brevipalpus obovatus females actively avoided leaf surfaces with elevated predator numbers; these females shifted their distributions and changed oviposition sites to leaf surfaces with fewer predators. In consequence, B. obovatus eggs on the upper sides of leaves were less frequently preyed upon than were those on lower sides. We suggest that upper leaf-surface exploitation in this particular herbivorous mite species mitigates predation risk from phytoseiid mites, which prefer lower leaf surfaces.

An Insect with Selective Control of Egg Coloration

“…Additionally, for selective egg pigmentation to be evolutionarily stable, at least two conditions would have to be met: (1) the ability to deposit eggs in locations where pigmentation is needed, resulting in a net increase in offspring survival, and (2) laying non-pigmented eggs in locations where pigment is unneeded being advantageous in some situations. For P. maculiventris, the first condition could be met if predation pressure is higher on the undersides of leaves, as has been observed in other plant-dwelling arthropod systems [12,15]. The upper surface of leaves would then represent ''enemy free space'' [30,31], and applying the pigment when eggs are laid there would minimize the cost of the resulting tradeoff in terms of higher UV radiation exposure.…”

“…We reasoned that the response of egg pigmentation to laying location in the previous experiment could be the expression of an evolved response to plant structure, which can modulate exposure to biotic and abiotic mortality factors [12][13][14][15]. Furthermore, although black and white oviposition substrates are not present in nature, the direction and intensity of light could change the apparent reflectance of plant leaf surfaces and elicit differences in egg pigmentation.…”

Stellate hairs on leaves of a deciduous shrub Viburnum erosum var. punctatum (Adoxaceae) effectively protect Brevipalpus obovatus (Acari: Tenuipalpidae) eggs from the predator Phytoseius nipponicus (Acari: Phytoseiidae)

“…A proximal factor causing upper leaf surface use may be tolerance to UVB damage (Fukaya et al 2013). On the other hand, influence of a generalist phytoseiid predator Phytoseius nipponicus Ehara (Acari, Phytoseiidae) on oviposition site choice of B. obovatus females was indicated in our previous study (Sudo and Osakabe 2013). Therefore, an issue of the possibility of habitat differentiation in adaxial-abaxial leaf surface distribution in mite taxa and its cost and benefit, especially in relation with their predators and solar UVB radiation, attracts us.…”

“…If the stellate hairs and adverse environment of the adaxial (upper) leaf surfaces, such as solar ultraviolet radiation (Ohtsuka and Osakabe 2009;Onzo et al 2010), hinder predators from accessing prey eggs, B. obovatus eggs might be protected from predation via the mother's oviposition site choice. A recent study revealed a generalist phytoseiid predator Phytoseius nipponicus Ehara (Acari, Phytoseiidae) preferred to stay on the lower side of a VEP leaf and B. obovatus eggs laid on the leaf upper side were preyed by P. nipponicus less frequently than on the lower side (Sudo and Osakabe 2013). On the other hand, it is not clear whether ovipositing among hairs or on adaxial leaf surfaces is advantageous to B. obovatus from the perspective of decreasing predation risk.…”

“…The proportion of B. obovatus eggs consumed by P. of VEP leaves reduce the predation risk of surfaces accessible to the mites, the daily fecundity of B. obovatus on predator-present leaves was approximately 5/6 that on predator-free leaves(Sudo and Osakabe 2013). It is considered the spatial segregation reduced opportunities for encounters between the predator and the prey, and hence the indirect negative effect of predator presence on…”