Comparative efficacy of some insecticides against purple scale insect , Lepidosaphes beckii ( Hemiptera : Coccoidea ) and its parasitoid in citrus orchard in Egypt

Five insecticide compounds Azadirachtin (Nimbecidine); Pyriproxyfen (Admiral); Acetamiprid (Mospilan); Emamectin benzoate (Proclaim) and summer mineral oil (star oil) and their mixtures were evaluated for controlling the purple scale insect, Lepidosaphes beckii (Newman) (Hemiptera: Diaspididae) as well as its parasitoid Aphytis lepidosaphes Compere (Hymenoptera: Aphelinidae) on growing citrus orchard, Citrus sinensis L. (Rutacea). This work has been carried out in the experimental farm of faculty of agriculture, Sabahia, Alexandria, Egypt, during two successive seasons 2009 and 2010. The obtained results revealed that star oil in combination with Admiral and Nimbecidine have given the highest reduction (%) values for L. beckii and its parasitoid, A. lepidosaphes during the two experimentally years. In 2009, the calculated reduction % values for L. beckii and A. lepidosaphes were (99.78 and 99.50%) and (96.75 and 97.29%), whereas in 2010 were (99.73 and 99.34%) and (94.40 and 96.46%) for the two combinations, respectively. On the other hand (Mospilan) and (Proclaim show less reduction percentages to the parasitoid during the two successive years. Whereas in 2009 were 54.56 and 73.19 %, in 2010 were 43.47 and 71.25 %, respectively.


INTRODUCTION
Egypt stands among the largest oranges producing countries in the world and occupies the third rank in production amongst the Mediterranean basin countries (FAO, 2011).Egyptian citrus has relation advantages in terms of yield and fruit quality, early ripening, relative low labor cost and nearness to international importing markets (Citrus Research Department, HRI, ARC, Egypt, 2012).Unfortunately, citrus trees are attacking by several insect pests among them the purple scale, Lepidosaphes beckii (Newman) (Hemiptera: Diaspididae ).
L. beckii is a polyphagous species that has been recorded from hosts belonging to 45 genera in 11 plant families including citrus which attacks leaves, trunk and fruit (Davidson and Miller, 1990).It is a major destructive pest of citrus in Egypt and is widely distributed throughout the tropical and subtropical regions of the world (Danzig and Pellizzari, 1998).L. beckii is consider as a very common armored scale insects infesting orange orchards in Alexandria Governorate.Heavy infestation causes chlorosis of leaves, defoliation, discoloration and poor maturation of the fruit and desiccation, weakening and dieback of the branches or even entire trees (Cohic, 1955 andGill, 1997)

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Damage to fruits occurs in heavy infestations, where spotting and often deformity of fruits affects market value.Areas surrounding scales on fruit remain green long after the rest of the fruit ripens.The areas surrounding the scale insects on leaves turn yellow and when severely infested the entire leaf may be discolored prematurely and be shed (Aly, 2011).
Aphytis lepidosaphes Compere (Hymenoptera: Aphelinidae) one of the most important bio-agent for controlling the purple scale in different regions of the world (Dean, 1961;Abdel-Fattah andEl-Saadany, 1978 andHafez et al., 1987 a andb).Hafez et al,1987b stated that the large number of L. beckii parasitized by the immature stages of Aphytis spp.were associated with the increase of living scales during January and February.The highest percentage of parasitism with the immature stages of Aphytis spp. was observed during the winter season, and the lowest percentage occurred during spring, summer and autumn.Extensive uses of chemical toxicants for pest control caused many problems, such as acute and chronic human and animal toxicity; development of insect resistance and environmental pollution (Malr, 1997).
Hence, the present work was initiated aiming to evaluate the efficacy of some insecticides and its mixture to control the most abundant scale insect L. beckii and its parasitoid A. lepidosaphes in citrus orchard in Alexandria, Egypt.

MATERIALS AND METHODS
Two field experiments 2009 and 2010 were carried out in the experimental farm of Faculty of Agriculture, Sabahia, Alexandria, Egypt to evaluate the efficacy of certain insecticides.The tested insecticide compounds were Mospilan ® , Proclaim ® , Nimbecidine ® , Admiral ® , Star oil ® , and their mixtures.The combination treatment, rate of application and sources of the used insecticides have shown in Table (1).The insect under study was the purple scale insect L. beckii as well as its parasitoid A. lepidosaphes on infested orange trees, Citrus sinensis L. (Rutacea).Ten treatments including the untreated (control) were replicated three times with three trees per replicate making a total of 90 orange trees, approximately having similar size, shape, height, and vigor.Spraying was accomplished by means of a conventional knapsack sprayer with a 20 liters tank.With ensure to complete coverage of all parts of each tree.Thirty leaves from each treatment were collected immediately before spraying and after 2, 4, 6 and 8 weeks of application.The picked samples were put in marked cloth bags and Comparative efficacy of some insecticides against purple scale insect, L. beckii 123 transferred to the laboratory for counting insects using the stereoscopic binocular microscope.To evaluate the efficiency of the tested compounds, the percentage of reduction was calculated according to the equation of (Stafford and Summers, 1963) for armored scale insect and (Henderson and Tilton,1955) for parasitoid.The data were analyzed through Randomized Complete Block Design.Analysis of variance and LSD value for comparing the mean of each treatment was adopted by (Snedecor, 1970).

RESULTS AND DISCUSSION
Our experiment was carried out during two successive years (2009 and 2010) at the end of the winter season before blooming and when the parasitoid individuals in a low level according to Hafez et al.1987b andAly, 2011, in order to evaluate the effect of five insecticide compounds Azadirachtin (Nimbecidine ® ); Pyriproxyfen (Admiral ® ); Acetamiprid (Mospilan ® ); Emamectin benzoate (Proclaim ® ) and the summer mineral oil (star oil ® ) and their mixtures against L. beckii and its parasitoid A. lepidosaphes.
The obtained data shown in (Tables, 2 and 3 and Figs 1 and 2) revealed that the two compounds mixtures Star oil+Admiral and Star oil+Nimbecidine were the most effective treatments against L. beckii throughout the experiment period 2009 and 2010.Whereas the reduction percentage for Star oil+Admiral was (99.78 and 99.50%), the reduction percentage for Star oil+Nimbecidine was (99.73 and 99.34%) in 2009 and 2010, respectively (with no significant difference).At the same time, the reduction percentage was (96.08 and 96.62%); (92.25 and 90.19%) and (86.07 and 96.62%) for Nembecidine, star oil and Admiral alone in 2009 and 2010, respectively.In addition, the two compounds mixture Star oil+Proclaim and Star oil+Mospilan gave (97.38 and 97.59%) and (97.04 and 96.65 %) reduction followed by Proclaim and Mospilan alone (91.45 and 87.49%) and (86.15 and 83.50%), respectively.Considering the probable occurring side effects of the tested compounds and there mixtures on the non-targeted parasitoid A. lepidosaphes (a main parasitoid of L.beckii) during 2009 and 2010, the data shown in (Table 4 and5 and Fig. 1 and 2) illustrate that Mospilan compound caused a lowest reduction effect (54.56 and 43.47%) followed ascending by Proclaim (73.19 and 71.25%), then the mixture Star oil+Proclaim (82.43 and 79.08%), Star oil (83.13 and 76.19%) and Nimbecidine (83.93 and 80.43%) with no significant differences between them.Then Admiral, Star oil+ Mospilan, Star oil+Admiral and Star oil+ Nimbecidine where they caused highest parasite reduction percentage reached (84.95 and 79.97%), (94.10 and 88.13% ), (96.75 and 94.40%) and (97.29 and 96.46%) in respect without no significant differences between the two mixtures compound, Star oil+Admiral and Star oil+ Nimbecidine.Comparative efficacy of some insecticides against purple scale insect, L. beckii 125 The obtained results agree with El-Deeb ( 2004) and Abo-Shanab ( 2005) whose stated that the use of insect growth regulators IGR S and oils mixtures increase and facilitate efficient control of scale insect pest due to the significant inhibition of the enzymes activity.Unfortunately, the obtained results were not agree with them in the probability of using IGRs in the integrated pest management program (IPM) because it gives adverse side effect on the Parasitoid of the Purple scale insect, L. beckii on citrus orchard.Moreover, our data was in agree with Grafton-Cardwall et al. (2006) who stated that using of IGRs reduced the target pest, California red scale Aonidiella aurantii Maskell (Hemiptera: Diaspididae) as well as its parasitoid Aphytis melinus De Bach (Hemenoptera: Aphelinidae) on citrus orchard.Interestingly, Blank et al. (1995) and Abdel-Razak (2007) suggested that the use of mineral oil treatment at 1-1.5% is the preferred choice in integrated pest management program.
Finally, it could be concluded that the most effective treatments for controlling the purple scale insect , L. beckii during winter months where the parasitoid wasps population occur in a low level, is using the mixture of Star oil+Admiral and/or Star oil+Nimbecidine.On the other hand, when the parasitoid population is high during summer and spring months we recommended the spraying with Mospilan which gives low reduction percentages to the Aphelinide parasitoid with more effect on the target insect pest.

Table 1 :
Type of treatments, rate of applications and the sources of it.

Table 2 :
Effect of tested treatments on the calculated reduction of Lepidosaphes beckii infested orange trees at Alexandria, Egypt.Spring 2009.

Table 3 :
Effect of tested treatments on the calculated reduction of Lepidosaphes beckii infested orange trees at Alexandria, Egypt.Spring 2010.

Table 4 :
Side effect of tested treatments on Aphytis lepidosaphes as a parasitoid of Lepidosaphes beckii infested orange trees in Alexandria, Egypt (spring 2009).

Table 5 :
Side effect of tested treatments on Aphytis lepidosaphes as a parasitoid of Lepidosaphes beckii infested orange trees in Alexandria, Egypt (spring 2010).