Host plant choice and location by larvae of the wheat bulb fly (Delia coarctata)

Abstract

Wheat bulb fly (Delia coarctata Fallen, Diptera: Anthomyiidae) is an important pest of winter wheat in the eastern half of the UK, and in northern and eastern Europe. The larvae must find a host plant and invade a tiller soon after hatching in late January. Chemical controls are costly and weather conditions may reduce their efficacy or prevent their application. Post‐emergence control relies on organophosphate insecticides, which may soon be withdrawn due to concerns about their negative health and environmental effects. Winter wheat (Triticum aestivum L.) is the preferred cereal host, but other winter cereals and related grasses may also be attacked, while oats (Avena spp.) are shunned. In choice test bioassays, neonate larvae chose couch grass (Elytrigia repens (L.) Nevski syn. Elymus repens (L.) Gould, Agropyearon repens (L.) Beauv.) seedlings and exudates over wheat seedlings and exudates, and exhibited geotaxis and negative phototaxis. Analysis of larval trails in choice test bioassays of seedling exudates showed that couch exudates are more attractive than wheat exudates, and that wheat exudates are more arrestant than couch exudates. This suggests that infochemicals isolated from couch, wheat, and oats could be used in wheat bulb fly control; possible delivery mechanisms are discussed. These findings, previous research, and a comparison of the phenologies and geographical distributions of D. coarctata and its hosts suggest that E. repens is the natural host of D. coarctata.

Wheat bulb fly, Delia coarctata, larval attraction to phenolic components of host‐plant root exudates

“…Arenas were the same as those used by Marriott & Evans () and Rogers & Evans (). In brief, they consisted of a black filter paper (Whatman 551; 90 mm diameter) placed in the centre of a glass Petri dish (140 mm diameter).…”

“…Larvae of WBF have been shown to locate host‐plant seedlings through chemotaxis (Scott, ; Greenway et al., ; Marriott & Evans, ), utilising Poaceae‐specific secondary plant metabolites, such as the hydroxamic acids DIMBOA (2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one) and MBOA (6‐methoxy‐benzoxazolin‐2‐one) (Rogers & Evans, ). Furthermore, when exposed to elevated levels of the primary plant metabolite CO 2 , WBF larvae are induced to intensively search an area (Rogers et al., ).…”

“…Adult female WBF do not oviposit in association with larval host plants, instead they oviposit in bare ground, in fallow or open canopy crops such as vegetables and potato (Petherbridge, 1921;Morris, 1925). This is thought to be because, in natural situations, bare earth is often colonised by couch grass (Elytrigia repens L.), the proposed natural host plant (Marriott & Evans, 2003), which is an aggressive coloniser of disturbed ground. In agricultural systems, these fields are often rotated into wheat and other cereal host plants, the eggs overwinter in the soil, hatching through January and February in the UK (Way, 1959), with the larvae infesting the seedlings of the new crop.…”

Wheat bulb fly (Delia coarctata, Fallén, Diptera: Anthomyiidae) larval response to hydroxamic acid constituents of host-plant root exudates

“…Seedlings for bioassays were prepared as follows, based on the methodology of Marriott & Evans (2003). Wheat seeds (cv.…”

Common volatiles are major attractants for neonate larvae of the specialist flea beetle Altica koreana (Coleoptera: Chrysomelidae)

“…At least five host-finding or host-selection strategies of holometabolous herbivorous insects can be identified based on the oviposition behaviour of adult females, feeding site selection and larval mobility: (1) females of some rooteating species lay eggs in the soil around the host plant (Jones and Coaker 1977;Ryan and Guerin 1982;Marriott and Evans 2003;Johnson and Gregory 2006); (2) females of the oligophagous chrysomelid Cassida denticollis Suffrian lay their eggs in the spring on dry plant material left over from annual plants of the previous year (Müller and Hilker 2000); (3) female codling moths lay their eggs predominantly on host foliage near fruit on which the neonate larvae feed (Geier 1963;Wearing et al 1973;Landolt et al 2000); (4) females of some polyphagous species do not distinguish host plants from non-host plants, but have highly mobile larvae (Janz and Nylin 1997;Foster and Howard 1999); and (5) some specialist species display high host fidelity in oviposition and always lay eggs on fresh host plant material (Larsen et al 1992;Keese 1998;Xue and Yang 2007).…”