Effect of clover root weevil larval feeding on growth of clover progenies from parents selected for tolerance in field trials

Abstract

The effects of larval herbivory by clover root weevil (CRW, Sitona lepidus) on seven white clover (Trifolium repens) and two red clover (Trifolium pratense) progenies from plants showing tolerance of CRW in field trials were tested in two controlled glasshouse experiments. CRW larvae recovered from red clover plants were, on average, fewer (6.3 larvae/g root dry weight) and shorter (5.7 mm/g root dry weight) than those from white clover (16.7 larvae, 7.1 mm length).This confirmed previous findings that red clover is an inferior host for this pest. In the first experiment, progeny of four of the white clover selections for CRW tolerance showed high tolerance (shoot dry weights (2.9% to '3.1% different from their respective weevil-free controls) compared with a 13Á24% shoot weight loss for two white clover cultivars. These results confirm field trial observations that there is variation for CRW tolerance in white clover and also that CRW tolerance is hereditable in at least some populations. The second experiment, on a smaller subset of white clovers, showed little effect of CRW on either the tolerant clover selections or the cultivar controls. An index of larval feeding pressure (larval numbers)larval projected areas/root dry weight) gave much lower values for the second experiment (12Á78 mm 2 / g) than for the first (69Á102 mm 2 /g). The absence of negative effects of CRW on the cultivar controls in experiment 2 was assumed to result from low CRW feeding pressure, allowing compensatory growth responses. A small but consistent increase in shoot: root ratio in the 'CRW treatment in experiment 1 provided supporting evidence for increased allocation to shoots as a mechanism for plants to reduce the impact of root herbivory. IntroductionEvaluations of white clover (Trifolium repens) and red clover (T. pratense) cultivars and experimental lines in on-farm trials in Northland (Cooper et al. 2003) and the Waikato (Crush et al. 2004 in the presence of clover root weevil (CRW, Sitona lepidus) showed differences among plant types. Vigorous, well-adapted white clovers are more tolerant of CRW than are less vigorous or poorly adapted white clovers, and red clover is more tolerant of

Clover root weevil tolerance of clover cultivars

“…Observations in New Zealand pastures have also suggested that white is the preferred type (Eerens et al 2001;Gerard & Crush 2003) but the latter also reported that CRW appeared able to habituate to red clover. Preferences by CRW adults for some white clover cultivars over others have been reported (Murray 1996b;Crush et al 2010) and, in field investigations, some lines of both white and red have shown increased tolerance of CRW feeding relative to others (Eerens et al 2001;Cooper et al 2003). also detected some resistance within two selections of red clover resulting from levels of formononetin that increased in response to CRW adult feeding.…”

“…This was more pronounced in May than October but indicates that a general statement of white clover being more favourable than red clover, based predominantly on adult feeding assays, is misleading. This investigation did not examine if CRW larvae perform less well on red clover than white (Crush et al 2010) and this should be further investigated particularly given reported habituation to red clover (Gerard & Crush 2003).…”

Comparison of New Zealand perennial clovers for resilience against common pasture pests

“…This cultivar was shown to be tolerant to clover root weevil soon after the pest established in New Zealand and as a consequence, has been included in later clover comparison research (e.g. Crush et al 2010;Ferguson et al 2016). The invertebrates had been and control leaves, either leaflets were removed from trifoliates of large leaved test cultivars or additional leaves added for small leaved cultivars.…”

Olfactory Receptor Neurons for Plant Volatiles and Pheromone Compounds in the Lucerne Weevil, Sitona discoideus

“…Of Palearctic origin, S. obsoletus is usually univoltine in northern hemisphere countries (Levesque and Levesque 1994;Markkula 1959), but because of New Zealand's temperate maritime climate it has two generations a year (Gerard et al 2010). It has a strong preference for white clover (Trifolium repens L.) (Crush et al 2010;Murray and Clements 1994), but elsewhere has also been reported as a pest of red clover (T. pratense L.) (Murray et al 2007). The weevil is now widely established across New Zealand (Hardwick et al 2016).…”