Date Published: March 8, 2019
Publisher: Public Library of Science
Author(s): Nicholas C. Manoukis, Roger I. Vargas, Lori Carvalho, Thomas Fezza, Shannon Wilson, Travis Collier, Todd E. Shelly, Nikos T. Papadopoulos.
Male Annihilation Technique (MAT) is a key tool to suppress or eradicate pestiferous tephritid fruit flies for which there exist powerful male lures. In the case of Bactrocera dorsalis (Hendel), a highly invasive and destructive species, current implementations of MAT utilize a combination of the male attractant methyl eugenol (ME) and a toxicant such as spinosad (“SPLAT-MAT-ME”) applied at a high density with the goal of attracting and killing an extremely high proportion of males. We conducted direct comparisons of trap captures of marked B. dorsalis males released under three experimental SPLAT-MAT-ME site densities (110, 220, and 440 per km2) near Hilo, Hawaii using both fresh and aged traps to evaluate the effectiveness of varying densities and how weathering of the SPLAT-MAT-ME formulation influenced any density effects observed. Counterintuitively, we observed decreasing effectiveness (percent kill) with increasing application density. We also estimated slightly higher average kill for any given density for weathered grids compared with fresh. Spatial analysis of the recapture patterns of the first trap service per replicate x treatment reveals similar positional effects for all grid densities despite differences in overall percent kill. This study suggests that benefits for control and eradication programs would result from reducing the application density of MAT against B. dorsalis through reduced material use, labor costs, and higher effectiveness. Additional research in areas where MAT programs are currently undertaken would be helpful to corroborate this study’s findings.
Males of many species of true fruit flies (Diptera: Tephritidae) are attracted to a small set of plant-derived secondary compounds termed male lures [1–3]. In the subfamily Dacini, males of the genera Bactrocera Macquart and Zeugodacus Hendel may be categorized broadly as responding either to methyl eugenol (ME) or raspberry ketone (RK) or its hydrolyzed form cue-lure (CL) [4,5] (but see [6,7] for recent data challenging this classification). It is widely believed , and limited field data support [8–10], that ME is a more powerful attractant than RK/CL. Why males respond to these lures was unknown until recently, but numerous studies (e.g., [11,12]) have now demonstrated that feeding on lures enhances male sexual behavior and signaling, which results in increased mating success.
The numbers of marked male B. dorsalis recaptured at the LPD traps for the 1d and 14 d old MAT grids and in the protein traps are given in Tables 2 and 3, respectively. The estimated male kill is also shown, calculated by multiplying the number captured in the LPD traps by 2 or 4 (for 220 and 440 spots/km2) to account for kills by the Jackson hats.
With the results of this study there is now increasing evidence supporting the hypothesis that the effectiveness of MAT with a powerful male lure, such as ME, is reduced when application density exceeds a relatively low threshold [31,32]. In the current study, the lowest application density (110 spots/km2) was the most effective as measured by estimated males killed, leaving the possibility that an even lower density might further increase effectiveness. The mechanism responsible for reduced catch in the higher application densities is not resolved, but the most likely hypothesis is interference: a large amount of lure in the air reduces the ability of individual males to follow odor plumes or gradients to point sources. This has been termed the “MAT-ME saturation hypothesis”, effected by the same principle at work in trap interference [43,44] and used for pest control via mating disruption (e.g. ).