Toxicity of Some Selected Pesticides against Neoseiulus barkeri (Acari: Phytoseiidae) Under Laboratory Conditions

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PJZ_49_1_155-162

Toxicity of Some Selected Pesticides against Neoseiulus barkeri (Acari: Phytoseiidae) Under Laboratory Conditions

Muhammad Zahid1, Muhammad Hamid Bashir1*, Bilal Saeed Khan1 and Muhammad Shahid2

1Department of Entomology, University of Agriculture, Faisalabad, Pakisan

2Department of Biochemistry, University of Agriculture, Faisalabad, Pakistan

ABSTRACT

Insect pests are the major yield decreasing factors in our agro-ecosystem. Among many pest management approaches, biological control is considered as the main strategy to address these issues including sucking pests. Different biocontrol agents are being used for the management of these sucking insect pests. Neoseiulus barkeri (Acari: Phytoseiidae) has been proved as an efficient acarine predator of sucking insect pests of different crops. This predator has also been reported from different localities of Pakistan. The main objective of this study was to screen out locally used pesticides i.e., pyriproxyfen, acetamiprid, chlorfenapyr, diafenthiuron and thiacloprid against N. barkeri in order to find its compatibility with some pesticides. Leaf disc arenas were used and leaf dip bioassay was conducted. Pesticides were tested for their compatibility with N. barkeri at different concentrations under controlled laboratory conditions. The results showed 25%, 30%, 70%, 50% and 65% mortality occurred by tested pesticides at field relevant doses after 144 h respectively. Missing mites data indicated repellency due to pesticides, was highest at the start of experiment, and then these acclimatized on leaf discs. Thiacloprid having lowest LC50 value 295 and proved toxic for the predator while diafenthiuron and pyriproxyfen have higher values. The findings of the study revealed that among five tested pesticides chlorfenapyr and thiacloprid proved moderately harmful for N.barkeri, hence cannot be recommended in IPM module.

Article Information

Received 04 April 2015

Revised 13 February 2016

Accepted 30 March 2016

Available online 14 November 2016

Authors’ Contributions

All authors took part in designing and planning the experiments. MZ performed the experimental work and wrote the article. MHB supervised the work.

Key words

Neoseiulus barkeri, Pesticides, Biological control, LC50, Compatibility

DOI: http://dx.doi.org/10.17582/journal.pjz/2017.49.1.163.170

* Corresponding author: [email protected]

0030-9923/2017/0001-0163 $ 9.00/0

INTRODUCTION

Sucking insect-pests pose major threat to agriculture through reduction of crop yields per unit area (Jeschke et al., 2011). Whiteflies, thrips, aphids and spider mites are major threat due to their vigorous feeding behavior and source of transmission of many plant diseases (De Barro et al., 2011; Amna et al., 2012; Sarwar, 2014). For getting rid off these notorious sucking pests, the main reliance is on synthetic chemicals as the immediate control strategy. But in parallel, the injudicious use of these chemicals is causing environmental hazards, human diseases and resistance in pest species (Abang et al., 2013). On the other hand, biological control is considered as ecosystem friendly pest management approach (Perdikis et al., 2008; Sarwar and Sattar, 2016). Predatory mites proved as successful bio-control agents of sucking mite and insect pests due to many attributes (Szabo et al., 2014). Numerous species of phytoseiids are commercially reared as bio-control agents of sucking pests of field and covered crops (Chant and McMurtry, 2007). The predatory mite Neoseiulus barkeri Hughes 1948 (Phytoseiidae) has been reported from Asia, America, Australia, Africa and Europe (de Moraes et al., 2004). It has received considerable attention regarding its capability to control whiteflies (Nomikou et al., 2003), thrips (Wu et al., 2014) and spider mites (Jafari et al., 2013) and rearing trials on wide temperature range (Jafari et al., 2012) proved it suitable for use in augmentative biological control programs. During recent years, integrated use of phytoseiids along with compatible reduced-risk pesticides has become popular approach (Damos et al., 2015).

The reduced risk pesticides have less detrimental effects as they are selective, target oriented and safer for the beneficial in contrast to conventional broad spectrum pesticides. Effects of several pesticides have been reported against predatory mites in different agricultural systems (Damalas and Eleftherohorinos, 2011; Lamberth et al., 2013; Poliane et al., 2014). Acetamiprid (Poletti et al., 2007; Beers and Schmidt, 2014), clofentezine and phosalone (Raudonis et al., 2004) thiamethoxam, thiacloprid, methoxyfenozide, pyriproxyfen, indoxacarbspinosad (Biondi et al., 2012), fenbutatin oxide, buprofezin, fenobucarb, imidacloprid, dinotefuran, validamycin, carbendazim and sulfur (Kongchuensin and Takafuji, 2006) had non-significant effect on immature developmental stages of different phytoseiids in contrast to pyrethroids, i.e., esfenvalerate, fenpropathrin, and rotenone were highly toxic (Villanueva and Walgenbach, 2005; Castagnoli et al., 2005). Pyrethrins and imidacloprid decreased fecundity and had negative effect against some phytoseiids and some studies revealed better performance of phytoseiids in integration with imidacloprid (Poliane et al., 2013).

In Pakistan, after the introduction of transgenic crops the major threat of sucking insect-pests particularly whitefly and spider mites has become very crucial (Rafiq et al., 2008; Ahmad et al., 2010) and huge investments are being spent on pesticides (Malik, 2014). By keeping in view the adverse effects of pesticides on biocontrol agents a study was planned to test pesticides at different concentration levels against N. barkeri (Acari: Phytoseiidae) to recommend the safer and compatible chemicals against sucking pests.

MATERIALS AND METHODS

Predatory mites culture

Native strain Neoseiulus barkeri (Acari: Phytoseiidae) reared under laboratory conditions since 2010 with no pesticides exposure, were used for the experimentation. The mass culture was reared on stored grain mite Rhizoglyphus tritici in growth chamber at 26±2°C, 65±5% R.H. and 12:12 (L:D) photoperiod. The culture was kept in small petri dishes (5.5 cm diameter) placed on water soaked foam in large petri dishes (14 cm diameter). The water served as barrier for the escape of mites.

Pesticides

The pesticides used are given in the Table I along with field relevant dose and trade names. These pesticides were purchased from local market. Serial dilutions were prepared in acetone starting from the field relevant dose, T1= Field relevant dose, T2=50%, T3=25%, T4=12.5%, T5=6.25% of field relevant doses and T6 =control (Acetone). There were four replicates for each pesticide concentrations and control.

Bioassay

Rearing arenas were prepared by using 14cm diameter petri dish along with 12cm foam soaked in water as barrier to prevent escaping of the predatory mites. Brinjal, Solanum melongena leaves (3 months old) were trimmed with cork borer to prepare leaf disc (1.7 cm diameter). The leaf discs were dipped individually in different concentrations for 10 seconds each and were allowed to dry at room temperature (Kongchuensin and Takafuji, 2006). These discs were placed upside down on the soaked foam. Newly emerged adult females (10 individuals) were released on each disc. Immature of R. tritici were offered as food on daily basis. These mites were added in the arenas to replace the consumed preys. Data on the mortality was recorded at 24 h interval basis till 144 h. The mites were considered dead if no movement in the appendages was observed on touching gently with the help of a fine needle. The absconded predators were excluded from data.

Table I.- Pesticides along with trade names, groups, concentration in ppm and field recommended doses.

Sr. No.	Name of pesticide	Trade name	Group	Concentration in sprayable material (ppm)	Recommended dose/acre/100ltrs. water
1	Pyriproxyfen	Priority 10.8EC	IGR	540	500 ML
2	Acetamiprid	Mospilan 20%SP	Neonicotinoid	300	150 GM
3	Chlorfenapyr	Pirate 360 G/LSC	Pyrrols	2700	75 ML
4	Diafenthiuron	Polo 50%SC	Thiourea	1000	200 ML
5	Thiacloprid	Talent 48%SC	Neonicotinoid	600	125 ML

Means sharing similar letter in a row or in a column are statistically non-significant (P>0.05); T1, Field relevant dose; T2, 1/2 of field relevant dose; T3, 1/4 of field relevant dose; T4, 1/8 of field relevant dose; T5, 1/16 of field relevant dose; T6, Control.

Statistical analyses

Data were analyzed statistically by calculating means, standard errors, percentages and two-way analysis of variance (ANOVA). Mortality due to pesticides was calculated by using Probit analysis and LC50 values were calculated with Minitab 17 Statistical Software (2010). Toxicity was evaluated according to IOBC criteria against beneficial arthropods (Jansen, 2010).

RESULTS

Pesticide at different concentrations and time intervals were tested against N. barkeri and harmless or slightly harmful and moderately harmful effects were observed. Highly significant mortality was observed at different concentrations (F= 41.06, 75.71, 255.34, 164.49, 192.13, df =5,108, P≤ 0.0000) and time intervals (F=10.62, 5.26, 35.42, 41.37, 24.03,df =5,108, P≤ 0.0000) for pyriproxyfen, acetamiprid, chlorfenapyr, diafenthiuron and thiacloprid respectively. Pyriproxyfen was harmless and maximum mortality (25%) was observed at field relevant dose (540 ppm) after 96 h while minimum mortality (2.50%) for 67.5 ppm after 24 h. Same value of the mortality was reported for T4, T5 after 24 and 48 h, respectively (Table II). Non-significant interaction regarding time and concentrations for mites escape (F=0.44, df =25,108, P=0.9899) and mortality (F=1.17, df =25, 108, P=0.2823) was observed (Table II). Acetamiprid was slightly harmful and caused maximum mortality (30%) at field relevant dose (300 ppm) after 144 h, while minimum mortality (2.50%) at 18.75 and 37.5 ppm after 24 hours and so on (Table III). There was non-significant interaction regarding time and concentrations for escape (F=0.19, df =25,108, P=1.0000) and mortality (F=0.44, df =25,108, P=0.9900) (Table III). Chlorfenapyr was moderately harmful for N. barkeri and maximum mortality (70%) was observed at field relevant dose (2700 ppm) after 120 h while minimum mortality (5.00%) was observed at 168.75 ppm concentration after 24 h interval (Table IV). There was non-significant interaction regarding time and concentrations for escape of mites (F=0.27, df =25,108, P=0.9998) and highly significant interaction for mortality (F=3.35, df =25,108, P≤0.0000) was observed (Table IV). Diafenthiuron also proved moderately harmful for N. barkeri and maximum mortality (50%) was reported at field relevant dose (1000 ppm) after 120 h, while minimum mortality (2.50%) was reported at 62.5 ppm concentration after 24 h (Table V). There was non-significant interaction regarding time and concentrations for escape of mites (F=0.20, df =25,108, P=1.0000) but a significant interaction for mortality (F=1.64, df=25, P=0.0441) (Table V). Thiacloprid was also moderately harmful for N. barkeri whereas maximum mortality (65%) was reported at field relevant dose (600 ppm) after 72 h while minimum mortality (2.50%) was reported at 37.5 ppm concentration after 24 h interval (Table VI). There was a non-significant interaction regarding time and concentrations for escape of mites (F=0.21, df =25,108, P=1.0000) and a highly significant interaction for mortality (F=3.68, df=25,108 P≤0.0000) (Table VI). The predatory mites escape from the arena were highly significant (F=5.51, df=5,108 P≤0.0001) (F=3.56, df=5,108, P≤0.0051) at different concentrations of pyriproxyfen and chlorfenapyr (Tables II and IV) (df=5, P≤0.0000) for acetamiprid, diafenthiuron and thiacloprid (Tables III, V and VI).

For statistical and other detail see Table I.

The escape of mites was found significantly different at different time intervals and remained non-significant (F=1.96, df=5,108, P=0.0907), (F=1.42, df=5,108, P=0.2218) for pyriproxyfen and diafenthiuron (Tables II and V) a significantly different (F=2.29, df=5,108, P=0.508) for acetamiprid (Table III), highly significant (F=3.20, df=5,108, P=0.0098) for chlorfenapyr (Table IV), and significant (F=2.47, df=5,108, P=0.0371) for thiacloprid (Table VI). Highest escape of predator was observed in the start of experiment, then no further escape could be due to acclimatization on leaf disc. The classification of pesticides toxicity against beneficial arthropods of our agro-ecosystem according to IOBC (International Organization for Biological Control) (Jansen, 2010) category under laboratory conditions was given in Table VIII. Probit analysis revealed LC50 values were varied according to all tested pesticides.

For statistical and other detail see Table I.

Table VII.– Cumulative LC50 values of tested pesticides against N. barkeri:

Pesticides	LC50	SE	95% Fiducial CI		Chi square	P Value
Pesticides	LC50	SE	Upper	Lower	Chi square	P Value
Pyriproxyfen	1279.93	478.69	478.6973	734.1133	2.130	0.546
Acetamaprid	405.292	74.45	300.3058	648.3242	4.951	0.175
Diafenthiuron	6314.55	971.60	4817.297	9102.761	0.694	0.875
Thiacloprid	295.516	22.58	254.3607	345.0062	1.259	0.739
Chlorfenapyr	985.609	82.54	832.7281	1163.507	0.222	0.974

CI, Confidence interval; P, Probability.

LC50 values after 144 h were 6314, 1280, 985, 405 and 295 for diafenthiuron, pyriproxyfen, chlorfenapyr, acetamiprid and thiacloprid respectively (Table VII). Thiacloprid was highly toxic for N. barkeri exhibiting the lowest LC50 value.

Table VIII.– Category of tested pesticides against N. barkeri.

Tested pesticides	Maximum mortality*	Standard mortality**	Categories
Pyriproxyfen	25%	0-25%	Harmless
Acetamiprid	30%,	26-50%	Slightly harmful
Diafenthiuron	50%	26-50%	Slightly harmful
Thiacloprid	65%	51-75%	Moderately Harmful
Chlorfenapyr	70%	51-75%	Moderately Harmful
__	__	>75%	Harmful

*, At field relevant dose up to 144 h; **, According to IOBC (Jansen, 2010).

DISCUSSION

Mortality and repellent effects due to tested pesticides varied significantly for N. barkeri (Acari: Phytoseiidae). Pyriproxyfen at field relevant dose had least harmful effects and these outcomes are in agreement with findings of Villanueva and Walgenbach (2005), who observed similar trend of mortality (1.3%), (5.0%) and missing (10.0%), (16.3%) at 105ppm after 24 and 96 h respectively, against Neoseiulus fallacis. Our results also matched with IOBC/wprs recommendations reported by Jansen (2010) that in field conditions pyriproxyfen at dose rate of 50grams active ingredients per hectare had moderately harmful effects against Typhlodromus pyri. Harmless effects of acetamiprid against N. barkeri were noted. These findings are in agreement with Beers and Schmidt (2014), who tested acetamiprid against Galendromus occidentalis at different dose rates i.e., 357(2X), 179(X), 18(0.1X) and 0 mg active ingredients per liter and found 36.00, 32.00, 40.00 and 0.00 percent mortality respectively. Villanueva and Walgenbach (2005) tested acetamiprid at dose rate of 115 ppm against Neoseiulus fallacis and observed mortality as (8.8%), (26.1%) and escape (8.8%), (17.0%) after 24 and 96 h respectively. Kongchuensin and Takafuji (2006) tested acetamiprid at 200ppm dose rate against Neoseiulus longispinosis and observed 60.2% mortality. These results are not in agreement to our findings which could be due to difference of species and experimental conditions. Poletti et al. (2007) tested acetamiprid at dose rate of 80mg active ingredients per liter against Neoseiulus californicus and Phytoseiulus macropilis and found comparatively less mortality (10.0%) and (2.0%) after 48 h. These difference of results could be attributed to difference of species and conditions. According to IOBC/wprs recommendations, acetamiprid was harmless against Typhlodromus pyri and Phytoseiulus persimilis. Our findings are in agreement with IOBC/wprs who declared acetamiprid safer against tested predatory mites. Results of our study revealed toxic effects of chlorfenpyr against N. barkeri, while Cloyd et al. (2006) observed different effects of chlorfenapyr against Neoseiulus californicus and Phytoseiulus persimilis and found (89%, 47%) survivors at 0.40 ml/2L dose rate and (85%, 52%) and at 0.81ml/2L dose rate respectively. Our results showed different mortality trend according to dose rate. Moderately toxic effect of chlorfenapyr was examined by IOBC/wprs. Its toxicity caused adverse effects on tested predatory mite and hence not recommended in IPM module. IOBC/wprs tested diafenthiuron at dose rate, 500 g active ingredients per hectare against Typhlodromus pyri and Phytoseiulus persimilis and found harmless and observed very slight toxic effects. Higher mortality percentage (50) at field relevant dose was observed. In the present results high mortality from diafenthiuron was due to formulation difference (50% SC) as compared to results of IOBC. The present study confirmed thiacloprid as toxic pesticide for predatory mites which is in agreement with findings of Vilanueva and Walgenbach (2005), who tested thiacloprid at 75ppm against Neoseiulus fallacis and found (2.5%) mortality and (12.5%) missing after 24 h and (14.8%) mortality and (12.4%) missing after 96 h. Similar results in our experiment regarding missing indicate repellent action of thiacloprid as same whereas high mortality in our experiment may be due to change in conditions and species under test. Our results are also in relevance to Cuthbertson et al. (2012), who tested thiacloprid at dose rate 0.45ml/L against four predatory mites, Neoseiulus cucumeris, Typhlodromips montdorensis, Iphiseius degenrans and Amblyseius swiriskii and found (18%, 4%, 56%, 10%) mortality after 24 h and (20%, 18%, 72%, 18%) mortality after 48 h respectively. Moreover IOBC/wprs, tested thiacloprid 480 SC against Typhlodromus pyri and observed slightly harmful effects. Our results are in disagreement with IOBC due to difference of species used in both cases.

CONCLUSION

Pyriproxyfen and acetamiprid were found harmless against Neoseiulus barkeri under laboratory conditions. These are selective pesticides and suggested to be used in recommended dose rates against their target pests. While diafenthiuron, thiacloprid and chlorfenapyr were toxic pesticides against tested predatory mite hence not recommended to be use in IPM module. However further research is still needed to study sublethal effects of these tested pesticides on further generations of this predatory mite.

ACKNOWLEDGEMENTS

The authors acknowledge Higher Education Commission (HEC) Pakistan for financial support in the form of Ph.D. indigenous scholarship schemes for completion of this piece of research work.

Statement of conflict of interest

Authors have declared no conflict of interest.

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