Evidence of density-dependent oviposition behaviour byListronotus bonariensis(Coleoptera: Curculionidae) in Canterbury pasture

Abstract

Argentine stem weevil (Listronotus bonariensis) (Kuschel) is a pasture pest of Lolium spp. in New Zealand and is the target of a classical biological control programme using the parasitoid Microctonus hyperodae Loan. However, laboratory experiments have indicated a strong density-dependent egg laying response which may have important implications for the biological control effort. Two field experiments were conducted using a manipulated range of weevil densities within 2.0-2.4 m~2 field enclosures and oviposition activity measured by weekly sampling of grass tillers within the enclosures. In both experiments, density had no effect on general oviposition behaviour although the percentage of tillers found to be infested with eggs increased significantly at higher densities. In experiment 1, L. bonariensis exhibited strong density-dependent oviposition with a significant decline in eggs/tiller/female with increasing adult density. An initial population of five L. bonariensis m~2 oviposited 32 times more eggs/tiller/female than 200 L. bonariensis m 2 . By comparison, density-dependent oviposition was absent in experiment 2 with eggs/tiller/female comparable for all densities. The dramatic difference between the two experiments in the expression of density-dependent oviposition was attributed to prevailing spring temperatures during the sampling interval, which in the second experiment were much cooler and delayed the onset of egg laying. It is probable that in experiment 2, oviposition was not regulated by density-dependent cues but limited by temperature and age related mortality in the adult population. The mechanism for density-dependent oviposition, its occurrence in the field and impact on the effectiveness of the parasitoid M. hyperodae are discussed.

Population Regulation of Argentine Stem WeevilListronotus bonariensis(Kuschel) (Coleoptera: Curculionidae) in Dryland New Zealand Pastures: a Multitrophic Interaction

“…Diffusive dispersal between sites of initially varying density can give temporal density dependence locally through its averaging effect (Kean and Barlow 2000). Density dependence detected in this study concurs with the evidence for density-dependent oviposition (McNeill et al 1998) and for density-dependent changes in North Island weevil populations (Barker et al 1989a).…”

“…These observations were made in dairy pastures in which tiller densities of Lolium perenne L. (cultivar Grasslands Nui) ryegrass averaged Ϸ4,200 m Ϫ2 (Barker et al 1984(Barker et al , 1986. In Canterbury, South Island, considerable research has been conducted on Lolium multiflorum ϫ perenne L. and L. perenne ryegrass species with densities Ϸ7,000 Ð 12,000 tillers m Ϫ2 , with or without irrigation, but under conditions of high soil fertility (Pottinger 1961, Fletcher 1986, Francis and Baird 1989, McNeill et al 1998). Density-dependent egg laying has been demonstrated in small experimental Þeld plots in Canterbury (McNeill et al 1998), but has not been detected in Þeld data .…”

Multitrophic interaction between the ryegrassLolium perenne,its endophyteNeotyphodium lolii,the weevil pestListronotus bonariensis,and its parasitoidMicroctonus hyperodae

“…Listronotus bonariensis is one of New Zealand's most severe pests of Gramineae and, because of this, its biology and ecology are now reasonably well understood (e.g., Pottinger 1961;Goldson 1981;Barker et al 1989;Goldson et al 1998;McNeill et al 1998). The mining habit of the weevil's larval stages kills both vegetative and flowering tillers (Pottinger 1961), while the adults chew off emerging cotyledons in newly-sown stands (Goldson & Penman 1979).…”

Caging overrides effects of density in laboratory‐based physiological estimates of reproductivity in Listronotus bonariensis (Coleoptera: Curculionidae)

“…In effect, and consistent with the findings of Goldson (1981b), caging was found to cause serious disruption to ASW reproductive activity. Moreover, although some density-dependent effects in the field are known (Barker et al 1989b;McNeill et al 1998McNeill et al , 2003Goldson et al 2011), these were never apparent among caged weevils. Kalvelage (1999), who conducted experiments in laboratory-reared weevils, also found few significant treatment effects and concluded that only weak density-dependent effects were to be found.…”