Oviposition response of scarabaeids: Does 'mother knows best' about rainfall variability and soil moisture?

Abstract

The effect of soil moisture on ovipositional preference is studied for four melolonthine scarabaeids, Holotrichia reynaudi, Holotrichia serrata and Dermolepida albohirtum, which are endemic to the semiarid tropics of India (Holotrichia spp.) and Australia, and Heteronyx piceus, which is endemic to the temperate and subtropical regions of Australia. As predicted by the preference-performance hypothesis, the three tropically adapted species show little or no ovipositional preference for soil moistures between permanent wilting point (−1500 kPa) and field capacity (−10 kPa) under either choice or no-choice conditions in their endemic soils, whereas H. piceus shows a clear preference to oviposit in drier soils (−1500 to −200 kPa). The ovipositional soil-moisture preferences of D. albohirtum and H. serrata are much narrower in geographically adjacent non-endemic soils (between −1500 to −200 kPa) than in their endemic soils. An analysis of daily rainfall determined the rainfall variability within the endemic areas of each species. The semiarid tropics are highly variable, with rainfall at the time of oviposition being a poor predictor of the future rain required for successful larval development, whereas the rainfall in the subtropics is much more reliable. The absence of a clearly preferred soil moisture for oviposition in the tropically adapted species appears to be a life-history strategy that allows these species to live in environments where rainfall is highly variable, and soil moisture at time of oviposition is a poor predictor of future environmental suitability for plant growth, and thus larval survival.