Helical shoot-tip mines on three genera of Asteraceae in Jamaica are caused by different species of Melanagromyza – Implications for the biological control of Chromolaena odorata using Melanagromyza eupatoriella

Abstract

Field host-range surveys and fixed plot trials were undertaken in Jamaica to gain an understanding of the host range of the fly Melanagromyza eupatoriella (Diptera: Agromyzidae), a potential biological control agent of the neotropical shrub Chromolaena odorata in South Africa. The fly larvae form helical mines in growing, vegetative stem tips, causing them to wilt and die. Seventy-seven sites at which C. odorata was present along with 30 other species of Asteraceae were surveyed for the presence of damage similar to that caused by M. eupatoriella. Twelve of these sites, chosen for the high (>10) number of M. eupatoriella mines present on C. odorata, were used to determine the abundance of 19 Asteraceae species encountered and the proportion of shoot tips with helical mines on each of these species. Similar mines were found on six species other than C. odorata: Mikania micrantha, M. cordifolia, Bidens alba, B. pilosa, B. reptans and Calea jamaicensis. Damaged plant material was field-collected from M. micrantha, C. odorata and B. alba and the causative herbivores (all Agromyzidae) were preserved for identification. Mines on Mikania species were longer than those caused by M. eupatoriella, and the species collected from M. micrantha was tentatively identified as Melanagromyza vulgata. Helical shoot-tip mines on Bidens species continued internally to completion further down the stem, unlike those of M. eupatoriella, where pupation occurs near the base of the helical mine. Only adult females were reared out of B. alba, therefore the fly could only be identified as a Melanagromyza species. The proportion of shoot tips with helical mines was highest on the two Mikania species, intermediate on C. odorata, and lowest on B. alba. For the quantitative, 12-site survey, five plant species in addition to C. odorata were present at four or more sites, and were significantly less likely than C. odorata to host M. eupatoriella. A fixed-plot trial was undertaken using two forms of C. odorata (plants from Jamaica and the southern African biotype), six Asteraceae (all encountered in the host-range surveys) and two crop species. Over 19 months, both C. odorata forms were attacked by M. eupatoriella and one mine was encountered on B. alba. The surveys, trials and identification of insects indicate that shoot-tip mines caused by M. eupatoriella were encountered only on C. odorata, out of 31 Asteraceae and two other plant species. Further laboratory-based host-range trials are required, should there be a need for this insect as a biocontrol agent in future.