Seasonal Variation in Foliar Mite Diversity and Abundance in Leaf Domatia of Three Native South African Forest Species

Abstract

Mite communities inhabiting plants are known to be affected by several environmental factors, including temperature and humidity. This pilot study aimed to assess seasonal variation in mite abundance and species richness in three Southern African woody species: Gardenia thunbergia, Rothmannia globosa (both Rubiaceae), and Tecomaria capensis (Bignoniaceae). Furthermore, we investigated the influence of rainfall, maximum and minimum temperature, and relative humidity on mite abundance and species richness. The study was conducted in 2014–2015 in Makhanda, formerly known as Grahamstown, in the Eastern Cape, South Africa. Twenty mature leaves were collected from all aspects of the plant fortnightly over 34 weeks. Following sampling, the leaves were viewed under a dissecting microscope, and mites were collected from inside the domatia and surrounding leaf surface area. Species diversity and abundance were calculated for each season and compared. A multiple linear regression analysis was performed in R Studio to test relationships between species richness and abundance, minimum and maximum daily temperatures, relative humidity, rainfall the day before, and accumulative rainfall over the preceding two-week period. We found that mites were present in the leaves of the sampled plants across all seasons, but that mite abundance and species richness changed with each season. None of the environmental variables were correlated with mite abundance, and only relative humidity influenced species richness. These results were not consistent across the three plant species studied, and we point to weaknesses in our sampling approach for the observed results. This pilot study, one of the first from southern Africa, provides a window into the complex interactions between plants and mites. We advocate for more studies on mite seasonality to better understand if it is specific to a region, vegetation type, or host species.