Suppression of female melon fly, Zeugodacus cucurbitae, with cue‐lure and fipronil bait stations through horizontal insecticide transfer

Abstract

Melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), is an important quarantine tephritid fruit fly with resident populations established in Hawai'i, USA. In the male‐annihilation approach, male flies are targeted using dispensers with cue‐lure (C‐L) and insecticides, typically organophosphates. The efficacy of the male annihilation approach is thought to be limited to individual male flies, contacting the lure and the pesticide, after which they die. Alternative classes of insecticides, such as fipronil, have been investigated for use in male‐annihilation. We hypothesized that ingestion of fipronil by male flies could lead to horizontal transfer and mortality in female flies. Horizontal insecticide transfer extends pesticide control beyond the individual contacting the toxicant through indirect contact via food sharing or other mechanisms. We tested the possibility for horizontal transfer of fipronil from male to female Z. cucurbitae through field and laboratory studies. Two repeated field trials were conducted to compare the numbers of female flies collected in fields treated with Amulet C‐L (0.34% fipronil active ingredient) bait stations, sanitation, and spot treatments of GF‐120 Fruit Fly Bait to numbers collected in fields where sanitation and spot‐treatments were used without Amulet C‐L. In fields with Amulet C‐L bait stations in conjunction with sanitation and weekly protein bait spot treatments of GF‐120 Fruit Fly Bait, female captures were significantly lower than those in field plots treated with weekly protein bait spot treatments and sanitation. In subsequent laboratory studies, all females died within 6 h after direct exposure to male flies that had access to Amulet C‐L for 1–4 min. The possibility that male regurgitant could be a mechanism for horizontal transfer and subsequent female mortality was determined by collecting regurgitated droplets from fipronil‐fed male flies and feeding them to males and females. Both male and female flies exposed to regurgitant from fipronil‐fed male flies or droplets containing fipronil had higher mortality than the male and female flies that were exposed to regurgitant or droplets with only the C‐L compound or sugar solution. Thus, female flies do experience mortality from exposure to regurgitant from males that have fed on fipronil laced solutions. This provides evidence of at least one mechanism of horizontal transfer of insecticide in tephritid fruit flies. These findings are discussed in the context of Z. cucurbitae integrated pest management programs in Hawai'i.

Comparative efficacy of a spider knottin insecticide, GS‐omega/kappa‐Hxtx‐Hv1a, against four species of invasive tropical tephritids

“…This was more pronounced following oral ingestion, where the full effects were not observed until 72 h post‐exposure. In comparison, Spafford et al, 2018 reported that male mortality approached 100% only 3 h following exposure, with female receivers following at 100% mortality by 6 h. In comparison, GS‐Hv1a‐dosed females directly treated in our study, only reached similar levels of mortality after nearly 72 h. After 24 h, mortality was only 25%, even at a concentration of 3.86%, the highest rate we tested. Additional research may be needed to determine an optimal dose of GS‐Hv1a to target females during this window while maintaining palatability.…”

“…Both lure and toxicant are impregnated in a small rectangular piece of fibreboard. Because fipronil is slow acting, the males are able to then transfer the insecticide to females they later contact (Spafford et al, 2018). This is advantageous, as female management is otherwise limited to on‐crop applications of less attractive protein‐based lures and broad‐spectrum insecticides, which require greater volume of product and can lead to non‐target effects on beneficial species (Vargas et al 2005).…”

“…This is commonly exploited for the management of urban pests such as cockroaches or ants; in many instances insect that have contact with a gustatory bait go on to spread it to conspecifics (Buczkowski et al, 2001; Buczkowski & Schal, 2001; Jordan et al, 2013). For males of many species of tephritids, a similar management approach focuses on courtship behaviours involving sex pheromones and regurgitant exchange between mating pairs (Drew & Lloyd, 1987; Spafford et al, 2018). Males of many species of tephritids are strongly attracted to compounds known as ‘male lures’, which include parapheromones and semiochemicals (Shelly et al, 2014).…”

“…The biological basis of the attraction varies and may include lekking signals (Whittier et al, 1994) or the compound may be a precursor for males to produce a mating pheromone (Tan et al, 2014). For many species, management is based on these male lures, and regurgitant exchange between mating pairs can occur (Drew & Lloyd, 1987; Spafford et al, 2018).…”

Interactions between integrated pest management, pollinator supplementation, and normalized difference vegetation index in pumpkin, Cucurbita maxima (Cucurbitales: Cucurbitaceae), production

“…Male annihilation technique consists of the deployment of high-density trapping stations with male-specific lures combined with an insecticide. The use of cuelure (the pheromone 4-(p-acetoxyphenyl)-2-butanone, which is highly attractive to male Z. cucurbitae ) laced with fipronil, has been used successfully against Z. cucurbitae and fruit fly species in genera Bactrocera (Spafford et al 2018). Among the biopesticides used in sub-Saharan Africa, Metarhizium anisopliae (Mechnikoff) Sorokin (Hypocreales: Clavicipitaceae) isolate ICIPE 69 (Real IPM, Thika, Kenya) is widely used as a fungal biopesticide (Akutse et al 2020) and has been found to be highly potent against Z. cucurbitae (Onsongo et al 2019).…”