Effect of simulated herbivory on bellyache bush (Jatropha gossypiifolia L.) growth and implications for biological control

Abstract

Understanding the ability of invasive plants to compensate for herbivory damage is crucial for their management, but this has been poorly studied in weed biological control. Bellyache bush (Jatropha gossypiifolia L.) is an invasive weed and a target for biological control in Australia. To understand the response of bellyache bush to herbivory, we simulated herbivory damage, under field conditions, at a site in north Queensland. Two size classes, that is, seedlings and mature plants were subjected to either defoliation, shoot damage or a combination of both, and the damage was inflicted once, twice or thrice at 6–7 weeks interval. All herbivory types significantly reduced growth and biomass when herbivory was inflicted twice or thrice, whereas the single application had limited impact. Shoot damage alone and defoliation + shoot damage had a greater negative impact than defoliation treatment on plant height, basal stem diameter, the number of leaves, root length and the number of shoot tips produced while increasing the number of dead shoot tips. Defoliation alone and defoliation + shoot damage had a greater negative impact on the number of flowers and fruit pods produced than shoot damage. The greater negative effects noticed when herbivory was inflicted twice or thrice suggest that multivoltine biological control agents that can inflict shoot damage and defoliation should be sought for the biological control of bellyache bush.

Post-release evaluation of a combination of biocontrol agents on Crofton weed: testing extrapolation of greenhouse results to field conditions

“…By removing the flies after one galling event per release, exposure of the plants to the flies was limited for strict comparison with the greenhouse trials. This may not completely represent true field conditions and as a multivoltine agent, the fly's impact might be greater than measured here (Kumaran et al 2018). In Hawaii, Crofton weed has been successfully controlled by the gall fly alone, where Crofton weed has been eliminated over large tracks of land, in low rainfall areas (Bess andHaramoto 1959, 1972;Muniappan et al 2009).…”

“…However, there is an increasing call not to release agents which are unlikely to be very effective (Paynter et al 2018;Raghu et al 2006) because of the risks associated with non-target effects. Therefore in addition to host specificity, the effectiveness of biocontrol agents is often assessed under controlled conditions in laboratory or greenhouse studies (Cowie et al 2017;Kumaran et al 2018;Morin et al 2009). However, under such controlled conditions the impact of the agents can be either under-or over-estimated, as these are not always representative of conditions in the field (Morin et al 2006(Morin et al , 2009Rosskopf et al 1999).…”

Prodiplosis hirsuta Kolesik sp. nov., a new species of gall midge (Diptera: Cecidomyiidae) feeding on shoot tips of Jatropha (Euphorbiaceae) in South America

“…Jatropha gossypiifolia is subject to herbivory and a suitable target for biological control in Australia (Kumaran et al . 2018). Simulated herbivory studies have indicated that J. gossypiifolia is susceptible to both defoliation and shoot damage.…”