Spinosad resistance in field populations of melon fly, Zeugodacus cucurbitae (Coquillett), in Hawaii

Abstract

BACKGROUND: Control of Zeugodacus cucurbitae, a serious agricultural pest worldwide, often includes or is dependent on the use of spinosad-based insecticides. This is especially the case in Hawaii, where GF-120, a protein bait containing spinosad as the active ingredient, has been in use as a key integrated pest management (IPM) tool against this Tephritid for the last two decades. Here, we report on resistance to spinosad [resistance ratios (RRs) and median lethal concentration (LC 50 )] in Hawaii's populations of Z. cucurbitae.RESULTS: High resistance was found in populations from three farms on Oahu (RR = 102-303; LC 50 = 191-567 mg L -1 ) and in a population from Maui (RR = 8.50; LC 50 = 15.9 mg L -1 ). These will be problematic for control given that the most concentrated dilution ratio on the GF-120 label is 96 mg L -1 of spinosad (1 part GF-120 to 1.5 parts water). Background resistance in a naïve wild population from the Island of Hawaii (RR = 2.73; LC 50 = 5.1 mg L -1 ) was relatively low compared with a spinosadsusceptible laboratory colony (LC 50 = 1.87 mg L -1 ). Resistance in the three Oahu and one Maui populations declined over generations in the absence of spinosad but remained elevated in some cases. Moreover, melon flies collected from one of the Oahu farms 1 year after the cessation of spinosad use revealed high persistence of resistance.CONCLUSION: Compared with a 2008 survey of spinosad resistance, our findings indicate a 34-fold increase in resistance on one of the Oahu farms over 9 years. The evolution and persistence of high levels of resistance to spinosad in Z. cucurbitae in Hawaii highlights the need for alternative control tactics, particularly rotation of active ingredients.

Knockdown of a Nicotinic Acetylcholine Receptor Subunit Gene Bdorβ1 Decreases Susceptibility to Oxa-Bridged trans- instead of cis-Nitromethylene Neonicotinoid Insecticides in Bactrocera dorsalis

“…32,33 Hence, alternatives such as spinosad-targeted nAChRs have recently been used to control Tephritidae pests including B. dorsalis worldwide. 34,35 Identification and characterization of nAChRs subunit is crucial for acknowledging their interaction with insecticides targeting nAChRs and eventually providing support for resistance management of B. dorsalis. In the present study, full-length nAChRs β1 cDNA (named Bdorβ1) from B. dorsalis was isolated and characterized based on the transcriptome data.…”

Field Tests of Three Alternative Insecticides with Protein Bait for the Development of an Insecticide Rotation Program to Control Melon Flies, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae)

“…However, lab-selected spinosad-resistant Z. cucurbitae (RR = 35.79) exhibited resistance to beta-cypermethrin (RR = 11) and low level resistance to avermectin (RR = 5.45) and no cross-resistance to trichlorfon and fipronil [ 48 ]. Our field sites on Maui was in very close proximity to where spinosad resistance (RR = 8.5) was detected in 2017 [ 17 ]. Resistance in that Maui population reverted to susceptibility within 6 generations in the absence of spinosad exposure in the lab.…”

“…Continuous year-round use of GF-120 has placed high selection pressure on Z. cucurbitae populations. A survey of spinosad resistance conducted in Hawaii in 2017 revealed up to 300-fold higher resistance to spinosad in melon fly populations collected from commercial farms on Oahu compared to a susceptible lab population [ 17 ]. The resampling of one of the Oahu populations one year after cessation of GF-120 use revealed that resistance persisted, albeit at a lower level (25-fold) [ 17 ].…”

“…A survey of spinosad resistance conducted in Hawaii in 2017 revealed up to 300-fold higher resistance to spinosad in melon fly populations collected from commercial farms on Oahu compared to a susceptible lab population [ 17 ]. The resampling of one of the Oahu populations one year after cessation of GF-120 use revealed that resistance persisted, albeit at a lower level (25-fold) [ 17 ]. A lower level of spinosad resistance was also found in a Maui population (8.5-fold) [ 17 ].…”

“…The resampling of one of the Oahu populations one year after cessation of GF-120 use revealed that resistance persisted, albeit at a lower level (25-fold) [ 17 ]. A lower level of spinosad resistance was also found in a Maui population (8.5-fold) [ 17 ]. The evolution and persistence of high levels of resistance to spinosad in melon flies highlights the need for alternative control tactics.…”