Less is more: Fewer attract-and-kill sites improve the male annihilation technique against Bactrocera dorsalis (Diptera: Tephritidae)

Authors: FEZZA, T - Animal And Plant Health Inspection Service (APHIS); SHELLY, T - Animal And Plant Health Inspection Service (APHIS); FOX, ABBIE - Animal And Plant Health Inspection Service (APHIS); BEUCKE, KYLE - California Department Of Food And Agriculture; ROHRIG, ERIC - Florida Department Of Agriculture And Consumer Services; Aldebron, Charlotte; Manoukis, Nicholas

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2024
Publication Date: 3/21/2024
Citation: Fezza, T., Shelly, T., Fox, A., Beucke, K., Rohrig, E., Aldebron, C., Manoukis, N. 2024. Less is more: Fewer attract-and-kill sites improve the male annihilation technique against Bactrocera dorsalis (Diptera: Tephritidae). PLOS ONE. 19(3). Article e0300866. https://doi.org/10.1371/journal.pone.0300866.
DOI: https://doi.org/10.1371/journal.pone.0300866

Interpretive Summary: Male Annihilation Technique (MAT) is a critical tool against certain invasive fruit flies that can attack many commodities by laying their eggs in fruit. MAT involves applying spots with a powerful male attractant and an insecticide at a high density across an area to be treated. This can kill such a high proportion of the males in a population that female's can't mate and the population is eliminated. The exact application density is examined here via "Mark-Release-Recapture" experiments in California and Florida with sterile oriental fruit fly (Bactrocera dorsalis) responding to MAT using methyl eugenol as an attractant. By counting the number of males brought to a subset of the spots that were placed in traps withing plots of varying MAT application density (spots per unit area) we were able to estimate the overall proportion killed. Results show that the customary application density of 230 spots per sq km (600 spots per sq mi) was not the most effective at killing male Bactrocera dorsalis; rather, reducing the application density by about 1/2 (to 110 spots per sq km) led to a much higher proportion killed. We believe this occurs because at the higher density there is too much attractant in the air, confusing the flies as they try to find a point source ("interference"). These results suggest that reducing the application density of MAT using methyl eugenol against oriental fruit fly would not only save labor and materials cost but would also increase the effectiveness of the technique.

Technical Abstract: The Male Annihilation Technique (also termed the Male Attraction Technique; “MAT”) is often used to eradicate pestiferous tephritid fruit flies, such as Bactrocera dorsalis (Hendel). MAT involves the application of male-specific attractants combined with an insecticide in spots or stations across an area to reduce the male population to such a low level that suppression or eradication is achieved. Currently, implementations of MAT in California and Florida targeting B. dorsalis utilize the male attractant methyl eugenol (ME) accompanied with a toxicant, such as spinosad, mixed into a waxy, inert emulsion STATIC ME (termed here “SPLAT-MAT-ME”). While highly effective against ME-responding species, such applications are expensive owing largely to the high cost of the carrier matrix and labor for application. Until recently the accepted protocol called for the application of approximately 230 SPLAT-MAT-ME spots per km2; however, findings from Hawaii suggest a lower density may be more effective. The present study adopted the methods of that earlier work and estimated kill rates of released B. dorsalis under varying spot densities in areas of California and Florida that have had recent incursions of this invasive species. Specifically, we directly compared trap captures of sterilized marked B. dorsalis males released in different plots under three experimental SPLAT-MAT-ME densities (50, 110, and 230 per km2) in Huntington Beach, CA; Anaheim, CA; and Sarasota-Bradenton, FL. The plots with a density of 110 sites per km2 had a significantly higher recapture proportion than plots with 50 or 230 sites per km2. This result suggests that large amounts of male attractant may reduce the ability of males to locate the source of the odor, thus lowering kill rates and the effectiveness of eradication efforts. Eradication programs would directly benefit from reduced costs and improved eradication effectiveness by reducing the application density of SPLAT-MAT-ME.