Eliminating the adult tephritid emergence from the soil can work side by side with other control measures such as chemical insecticides, bait sprays, soil moisture management, soil compaction, sterile insect release, and male annihilation in eradication programs (Ndlela et al. 2016; El-Gendy and AbdAllah 2019, 2020). In the present study, the tested insecticides were effective in PFF eradication, with different toxicity against PFF pupae and adult flies. Pupal mortality rates depended on the chemical sub-group of the insecticide, reflecting 90-99% of the variability, according to the determination coefficient. It also depended on the insecticidal concentration. For instance, the highest real mortality was obtained with the highest concentration of imidacloprid (99.0%), followed by diazinon (94.44%), and then abamectin (90.0%). Furthermore, diazinon and abamectin can eliminate adult flies at any of the tested concentrations. However, the highest concentrations of imidacloprid are needed to perform similarly.
Diazinon was the most toxic insecticide for the pupal stage, followed by the two biopesticides abamectin and then imidacloprid. These results are in agreement with the results of Stark et al. (2014) who mentioned that diazinon, as a soil treatment, was of the most toxic insecticides against Ceratitis capitata pupae, but neither B. dorsalis nor B. cucurbitae. In parallel, diazinon was the most toxic insecticide for PFF male and female flies with 0.20 and 0.26 ppm at 24 h post-treatment, followed by malathion, lufenuron, and methoxyfenozide insecticides (Mosleh et al. 2011). Also, Abdullahi et al. (2020) revealed that the diazinon was the most toxicity of the insecticides against B. invadens, followed by chlorpyrifos, cypermethrin + dimethoate, and deltamethrin, respectively. In the same line, Stark et al. (1992) found that puparium formation was pesticide concentration-dependent, affected by diazinon, not by cyromazine.
In many fruit fly studies, abamectin 1.8% EC exhibited a high efficiency against various fruit flies stages. According to Halawa et al. (2013), in sandy-soil treatments against 3 days old pupae of PFF and C. capitata, abamectin was the most effective treatment, compared to lufenuron or lufenuron + emamectin benzoate. Also, abamectin was of the most effective insecticides against B. dorsalis adults (Wang et al. 2013). However, imidacloprid obtained the lowest efficiency of the tested insecticides, emamectin benzoate, trichlorfon, and λ-cyhalothrin, against PFF (Khan and Naveed 2016).
PFF response to the tested insecticides varied significantly, which may be due to the insecticide type, mode of action, or residual activity. The present findings are consistent with El-Aw et al. (2008), who reported different toxicity rates of pesticides against PFF adults, where methomyl was the most effective insecticide, followed by thiamethoxam, spinosyn, and malathion. Stark et al. (2014) mentioned that the most effective insecticides as soil treatments for C. capitata, B. cucurbitae, and B. dorsalis pupae were spinosad, lambda-cyhalothrin, permethrin, tefluthrin, and diazinon with no significant difference. However, Raga et al. (2018) mentioned that Anastrepha fraterculus (Wied.) and A. grandis (Macquart) exhibited similar susceptibility to acetamiprid, deltamethrin, flypyradifurone, imidacloprid, phosmet, thiamethoxam, and zeta-cypermethrin.
Recently, the Agriculture Pesticides Committee in Egypt banned diazinon for agricultural uses. However, residues of diazinon have been found in some Egyptian areas. Diazinon was detected in water samples collected from Lake Qarun and drainage canal in Damietta, Egypt (Abdel-Halim et al. 2006). Its residual effect extended to crop fruits, where fruit samples in oranges and grapes contained 0.01 mg/kg of diazinon (Gad Alla et al. 2015). Hence, it is clear that the importance of finding effective bio-insecticides against immature stages of fruit flies other than diazinon as soil treatments, such as abamectin.
The present study also revealed a decrease in fly AChE activity of previously insecticide-treated pupae. The percentages of AChE activity inhibition were in ascending order for abamectin, diazinon, and imidacloprid. The activity of AChE in treated PFF with malathion, diazinon, methoxyfenozoide, and lufenuron decreased compared to the control (Mosleh et al. 2011), as well as variations among tested insecticides in AChE activities in PFF adult flies treated as pupae were reported (Halawa et al. 2013). The present findings of AChE inhibition by the tested insecticides is found to be dependent on time after treatment, which was positively correlated to the tested time post-treatment in both abamectin and diazinon insecticides, 24, 48, and 72 h, with a maximum inhibition at 72 h, followed by 48 and 24 h, respectively. As for imidacloprid, AChE inhibition was high after 24 h, followed by 72 and then 48 h.
As a bio-pesticide, abamectin had a high efficacy eliminating immature stages of PFF in the soil, as well as the emerged flies from the treated pupae. Thus, abamectin soil treatment abamectin might be used as an alternative to diazinon for the control program of PFF.