Maintenance of a narrow host range by Oxyops vitiosa; a biological control agent of Melaleuca quinquenervia

Abstract

Host range expansion in insect herbivores is often thought to be mediated by several factors, principal among them are secondary plant metabolites. In weed biological control, the host range of a prospective agent is one of the most important considerations in its implementation. Extensive host testing tests seek to determine the behavioral acceptance and nutritional value of different test plant species to the potential agent. A list of test plants is compiled that comprises species that are close taxonomic relatives of the target weed plus other species of economic or ecologic importance. The host testing of the Melaleuca quinquenervia biological control agent Oxyops vitiosa indicated that larvae would accept and complete development on the Australian target weed M. quinquenervia, two Australian ornamental species, Callistemon citrina, Callistemon viminalis (all Myrtaceae). However, the larvae did not complete development when fed a North American species Myrica cerifera (Myricaceae). The study reported here confirms these results and examines the nutritional and performance differences in O. vitiosa larvae fed leaves of these species. The leaf quality factors, percent moisture, percent nitrogen, toughness, and terpenoid content were related to larval survival, performance and digestive indices. The results indicate that plant quality among the Myrtaceae species was generally similar and correspondingly larval survival, performance and digestive indices differed little when larvae were fed leaves of these species. However, This article is a U.S. government work, and is not subject to copyright in the United States.significant differences occurred in the plant quality of the North American M. cerifera compared with the Australian species which had leaves with the lowest percent moisture, lowest leaf toughness, highest percent nitrogen. This species, however, is not a physiological host as none of the neonates survived to pupate. When third instars were switched to M. cerifera from their normal host M. quinquenervia reductions were found in survival, biomass gain, digestive efficiency, and conversion of digested food to insect biomass. The marginal acceptance of this North American native plant in laboratory bioassays appears related to the terpenoid chemistry that has similarities to the taxonomically unrelated host M. quinquenervia. However, the high larval mortality corresponds to several novel terpenoids that are not present in the host. For weed biological control host testing these results indicate that M. cerifera is a poor host for O. vitiosa. Additionally, future test plant lists should include plants with secondary metabolites similar to the target weed as these compounds may constitute behavioral cues that are relevant to these specialized herbivores.Published by Elsevier Ltd.

Physiological host range of Ceratapion basicorne, a prospective biological control agent of Centaurea solstitialis (Asteraceae)

“…The exceptions presumably are caused by evolutionary divergence of critical characters (e.g., allelochemics and plant morphology) in close relatives that cause them to be less suitable, and evolutionary convergence in more distant relatives that make them more suitable. Thus, selection of plant species to test should not rely only on phylogeny, as some have proposed (Briese, 2005(Briese, , 2006, lest we overlook a more distant relative that may be suitable because of similarity of critical characters (e.g., Wheeler, 2005;Haines et al, 2004).…”

New Combinations in Melaleuca for Australian Species of Callistemon (Myrtaceae)

“…The 15 test plant species are listed in Table 4. All were Myrtaceae except Morella cerifera (L.) Small (Myricales: Myricaceae), which was considered at risk (Wheeler 2005;Pratt et al 2009). Two specimens of Eugenia DC.…”

Characterising insect plant host relationships facilitates understanding multiple host use

“…Biological control practitioners now recognise, for example, the differences between the fundamental host range of a species (absolute limits to an insect's host range) and its realised host range (the set of hosts actually used in the field; Sheppard et al 2005;van Klinken 2000b). The potential causes of these differences are appreciated, but not yet fully understood, and include such processes as metabolic and sensory capabilities, prior experience, physiological status of the insect, time-dependent behavioural changes, host plant availability and differences in host plant quality (Barton Browne and Withers 2002;Marohasy 1998;Sheppard et al 2005;van Klinken 2000a;van Klinken and Heard 2000;Wheeler 2005). In practice, therefore, considerable room for improvement of testing methodology remains.…”