Listronotus bonariensis

The Argentine stem weevil is a small grey insect up to long, with a waxy covering. Soil particles adhere to this wax, and while the insect remains stationary, which it often does, this makes it well-camouflaged and difficult to spot. The larvae are cream-coloured grubs with brownish heads. ==Distribution==

The Argentine stem weevil is native to South America where it is present in Brazil, Uruguay, Argentina, Bolivia and Chile. In these countries it is not considered to be economically important. ==Ecology==

This weevil feeds on a number of crop plants including perennial ryegrass, on which it is a major pest, Italian ryegrass, other grasses, wheat, barley, oats and maize. It is usual for only one larva to be present in each tiller. Attempts have been made in New Zealand to biologically control the Argentine stem weevil. The braconid wasp Microctonus hyperodae is a parasitoid of the pest in South America and has been introduced to control it. The wasp has become established in the North Island and appears to be reducing populations of the weevil. Another wasp Microctonus aethiopoides had previously been introduced in order to control the clover root weevil (Sitona lepidus), and it has also been found to parasitize L. bonariensis. Several species of endophytic fungi, especially Acremonium spp., have also been studied with a view to biological control in New Zealand. Their presence inside the crop plant deters egg-laying by the weevil and reduces the damage done by the larvae, however Acremonium lolii renders perennial ryegrass toxic to livestock at some stages of growth, putting them at risk of developing the disease perennial ryegrass staggers. ==References==