Evaluation of Comparative Toxicity of Different Insecticides against Fruit Fly, Bactrocera zonata Saunders (Diptera: Tephritidae)

Rashid Ahmed Khan* and Muhammed Naveed

Plant Protection Division, Nuclear Institute for Agriculture and Biology, Jhang Road, Faisalabad, Pakistan

ABSTRACT

Bacterocera zonata (Saunder) (Diptera: Tephritidae) is a major pest of fruits causing severe losses to the fruit production and quality in Pakistan. Its management has largely relied upon the indiscriminate and injudicious use of conventional insecticides resulting in problem of insecticide resistance, environmental pollution, fruit contamination and health hazards. The major goal of the present study was to evaluate the effectiveness of a bio-insecticide, emamectin benzoate with other conventionally used insecticides against B. zonata. The results revealed the high toxicity of emamectin benzoate with LC50 value of 38.25 followed by trichlorfon, λ-cyhalothrin and imidacloprid with LC50 values of 44.21, 58.98 and 187.81 ppm, after 24 h post treatment, respectively. Based on our experimental results it is concluded that emamectin benzoate is an effective and environmentally safe alternative to the other conventional insecticides used for the management of B. zonata.

Article Information

Received 03 June 2016

Revised 03 October 2016

Accepted 16 October 2016

Available online 11 January 2017

Authors’ Contributions

RAK conceived and designed the study, performed analysis and wrote the article. MN performed experimental work and helped in data collection.e

Key words

Bactrocera zonata, Conventional insecticides, Emamectin benzoate, Environmentally safe insecticide, LC50.

* Corresponding author: rashidpp2004@yahoo.co.uk

0030-9923/2017/0001-0399 $ 9.00/0

Copyright 2017 Zoological Society of Pakistan

DOI: http://dx.doi.org/10.17582/journal.pjz/2017.49.1.sc7

The fruit flies belonging to the family, Tephritidae which are known as the major pests of soft, fleshy fruits and remains the most significant order of dipterous pests of polyphagous nature (Robison and Hooper, 1989). Among the fruit fly, the peach fruit fly, Bactrocera zonata (Saunders) is the most abundant and severe pest infesting fruit orchards throughout the world (Anthony et al., 2005). This species attack fruit species such as mango, peach, guava, citrus, apricot, apple and fig. Besides fruits, it infests some vegetables such as pepper, tomato and eggplants as alternate hosts (El-Gendy, 2012; Ghanim, 2009; Hashem et al., 2004; El-Minshawy et al., 1999; White and Elson-Harris, 1992; Liquido et al., 1990; Kapoor and Agarwal, 1982).

The genus Bactrocera poses a serious risk to the horticultural crops owing to the wide range of hosts and invasiveness nature of the genus (Clarke et al., 2005). According to an estimate, losses recorded in fruits without management have been 21% in Pakistan (Stonehouse et al., 199 7). Among the fruits infested by fruit flies in Pakistan are apple, ber, guava, mango, musk melon and bitter gourd (Khan and Musakhel, 1999; Sultan et al., 2000; Khan et al., 2005). Two well-known species of fruit flies in different parts of Pakistan include peach fruit fly, B. zonata (Saunders) and cucurbit fruit fly B. cucurbitae (Coquillett). In Pakistan, incidence and abundance of B. zonata has been recorded in areas of Baluchistan and Sindh near the coastal and sub-coastal, as well as semi-arid areas and plains of the northern Punjab. Its presence has been observed as an occasional pest in Peshawar valley and from the foothills of Islamabad (Marwat et al., 1992). A variety of insecticides like dipterex, triazophos, imidacloprid, and neem products are generally used to control the fruit flies.

The present study evaluated the toxicity of emamectin benzoate and compared it with other conventional insecticides used against B. zonata.

Materials and methods

Adults of B. zonata used in this study were isolated from the field infested fruits collected from orchards in Faisalabad, and then maintained in the rearing laboratory. The emerged larvae from the fruits were provided moist sand for pupation. These pupae were then isolated by wire mesh and placed in the Perspex cages for adult emergence.

Table I.- Details of insecticides used in the experiment for their comparative toxicities.

Active ingredient | Trade name | Formulation | Manufacturer | Dose range (ppm)
Emamectin benzoate | Proclaim® | 19 EC | Syngenta | 31.25-500
Trichlorfon | Diptrex® | 800 SP | Bayer | 31.25-500
λ-Cyhalothrin | Karate® | 2.5 EC | Syngenta | 31.25-500
Imidacloprid | Confidor® | 200 SL | Bayer | 31.25-500

Bioassays were performed under standard laboratory environment of 25± 5 ºC, 45±5% RH, 14:10 L photoperiod. The insecticides tested in this study were, Proclaim® 19 EC (emamectin benzoate), Diptrex® 800 SP (trichlorfon), Karate® 2.5 EC (λ-Cyhalothrin) and Confidor® 200 SL (imidacloprid). Distilled water was used as a control. Stock solutions of 500 ppm of all the insecticides were freshly prepared in distilled water and serially diluted four times to get the final concentration of 250, 125, 62.5 and 31.25 ppm, respectively (Table I).

Table II.- LC50 values of different insecticides on adult B. zonata after 24 h post-treatment.

Treatments | LC 50 (Fiducial Limits) | LC 90 | Slope±SE | χ 2 | TR*
Emamectin benzoate | 38.25 (27.15-53.56) | 238.74 | 1.61±0.24 | 0.99 | 4.91
Trichlorfon | 44.21 (33.9-57.41) | 297.57 | 1.54±0.23 | 0.65 | 4.25
λ-Cyhalothrin | 58.98 (54.17-64.19) | 511.40 | 1.36±0.21 | 7.21 | 3.19
Imidacloprid | 187.81 (124.65-283.89) | 1044.72 | 1.71±0.22 | 3.31 | 1.00

*Toxicity Ratio.

All the serially diluted solutions were applied to the 25 ml capacity transparent glass vials using a cotton swab and allowed to dry for 30 min. The experiments were replicated three times, each time using 10 adults per treatment. Residual contact toxicity was recorded after 24 h as percentage mortality.

All the bioassay data were subjected to probit analysis (Finney, 1971) using PoloPlus probit analysis software. Probit mortality graphs were prepared in MS-Excel 2007.

Results and discussion

The contact residual toxicity of the insecticides showed varying degrees of toxicities. Table II shows LC50, LC90 and toxicity ratios of different insecticides against B. zonata adults. The gradation of toxicity of insecticides against adult B. zonata is Emamectin benzoate > Trichlorfon > λ- Cyhalothrin > Imidacloprid.

Emamectin benzoate proved to be the most effective among the insecticides used. It is an abamectin semisynthetic derivative, developed for the control of lepidopterous pests on vegetables worldwide (Jansson and Dybas, 1997; Babu, 1988). It raises the level of release of the neurotransmitter, γ-aminobutyric acid (Jansson and Dybas, 1997), which irreversibly paralysed the target invertebrates and causes death. Moreover, it displays the translaminar activity which is a characteristic of systemic insecticides. Emmamectin applied leaves retain a pool of active ingredient, consequently pest control achieved as a result of feeding by the larvae (Ishaaya et al., 2002). Degradation of emamectin benzoate on the surface of plant is quite fast (López et al., 2011) resulting in the minimum exposure to beneficial agents (Ishaaya et al., 2002).

In an earlier experiment, a bio-insecticide proclaim was found effective against B. zonata in a very low concentration (Fetoh et al., 2009). Our experimental results are in line with their results.

Tricholofon and λ-cyhalothrin are comparatively effective, which raises questions of development of insecticide resistance against populations of B. zonata. In an earlier experiment, high level of trichlorofon resistance and moderate level of λ-cyhalothrin resistance has been documented. The level of resistance in their experiment remained at 1.00 to 41.82 fold for trichlorfon and 1.07 to 18.24 fold for λ-cyhalothrin, respectively (Nadeem et al., 2012).

Imidacloprid proved to be the least effective in our experiment among the insecticides used. It may be due to its systemic mode of action and low residual toxicity. In the literature, there are conflicting reports of imidacloprid effectiveness. In one report imidacloprid was found to have LC50 value of 211 ppm with low level of resistance (Haider et al., 2011), whereas other reports suggest satisfactory results (Yee and Alston, 2006) with the use of imidacloprid.

Conclusion

Our present findings suggest that emamectin benzoate is comparatively a safe alternative to the insecticides in use for the control of B. zonata. Its use may also encourage beneficial organisms for being less toxic.

Conflict of interest statement

We declare that we have no conflict of interest.

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