INTRODUCTION

          Citrus red-scales, insect Aonidiella aurantii (Maskell) generally causes yellow chlorotic spots when attacking leaves. Yellow spots may also appear at the feeding sites on fruit. This insect appears to prefer fruit over leaves in the summer and fall; therefore, the fruit may be heavily infested, while the adjacent leaves are relatively free from them. Unlike other armored scales on citrus, the insect restrict feeding on foliage and fruit but do not attack twigs or limbs of citrus trees. Large populations of this scale insect may result in severe defoliation and fruit production would be decreased. The insect presents on the fruit will render it as unmarketable fresh fruit because it does not agree with the consumer desire. Heavily infested fruit may be downgraded in the packinghouse and, if population levels are high, serious damage can occur to trees. Severe infestations cause leaf yellowing and drop, dieback of twigs, limbs, and occasionally death of the tree. Tree damage is most likely to occur in late summer and early fall when its population is high and moisture stress on the tree is sever (Kennett et al., 1999)

Egyptian citrus considered one of the popular and cheap fruits. Citrus trees are subjected to varieties of insect pests, as the armourd scale insects, mainly the red scale insect, A.aurantii (Habib et al., 1971, Darwish, 1970 and Farag et al., 1989).Orange has become the most commonly grown fruit tree in the world. Large quantities of fresh oranges and orange juice concentrate are exported to the United States and small shipments go to East Germany, Canada and Argentina. However, overproduction has glutted domestic markets and brought down prices and returns to the farmer to such an extent that plantings have declined (Florida Citrus Pest Management Guide, 2007). Because of the damage caused by this insect to citrus trees, different control

methods had been adopted by many investigators to prevent serious losses to the citrus crops in Egypt.

          Local sprays of mineral oils are used for many years against scale insects, mealy bugs, thrips, aphids and mites on different crops and fruit trees, (El-Deeb et al., 2002 and Moursi, 1996). These oils were most commonly used in horticulture to control scale insects and mites (Chapman et al., 1952). Micks and Berlin (1970) and El Sebae et al., (1976) stated that resistance was not recorded for mineral oils which still have the advantage of being effective against the insect resistant strains.

            Present study was carried out to evaluate some insecticides against citrus red-scale, [Aonidiella aurantii (Maskell)] and find out the most effective one, which could control infested orange trees successfully and synchronizely by the same application in an attempt to reduce its serious damage on citrus fruits.

MATERIALS AND METHODS

Two field experiments were carried out (during pre-flowering stage in early spring (2010) and during fruiting stages in early summer (2011)),in an orchard of orange trees at Kafr-Eldwar, El-Beheira Governorate, to evaluate the efficacy of certain compounds[five emulsifiable concentrate light summer mineral oils differ in its purification percentages (Super Masrona oil^® 95%; Diver oil^® 97%; Tiger oil^® 97%; Kz oil^® 95% and CAPL2 oil^® 96.62%) and Imidacloprid insecticide (Admire® 20% as soluble concentrate formulation)]against the armored scale insect[citrus red-scale, Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae).Orange trees were 15 years old and have similar uniformity in height, shape and sizeand highly infested with citrus red-scale insect. 

Experiments were designed as a complete randomized block design. Spraying was accomplished by means of a conventional knapsack sprayer with a capacity of 20 liters/tank; at rate of 10-12 liters per tree to ensure complete coverage of all parts of the tree. Six treatments as well as the untreated check were replicated four times with six trees per replicate and randomly distributed over 168 trees. Random samples of thirty leaves from each replicate were selected for laboratory counts (0, 2, 4, 6 and 8 weeks) before and after spraying. Samples were put in labeled cloth bags and transferred to the laboratory for counting using the stereoscopic binocular microscope.The reduction of the inspection of both insects numbers was expressed as reduction percentages which were calculated according to Henderson and Tilton (1955). Statistical analysis of variance and LSD value for comparing the mean effects of each treatment were adopted according to Snedecor (1961).The tested compounds are shown in Table (1) .

Table 1: the used insecticides in the evaluation

RESULTS AND DISCUSSION

All tested treatments showed ascending increasable effect with time intervals against the tested insect during the two experiments periods.It was observed that the reduction of the tested insect populations caused by Mineral oils increased directly proportional with their purification percentages.

A) Effect of tested compounds during pre-flowering stage

L.S.D_0.05 (Means)= 1.59

Figure1: Efficacy of tested  insecticides  against the citrus red-scale insect Aonidiella aurantii (Maskell) infested orange trees, at Kafr-Eldwar, El-Beheira Governorate, during pre-flowering stage (2010).

Data in Fig. (1) illustrate the effect of the tested compounds against the citrus red-scale Aonidiella aurantii (Maskell) insect (Hemiptera: Diaspididae) during pre-flowering stage. Data show that reduction percentages increased by increasing the time after treatment, where the highest reduction percentages for all tested chemicals appeared after eight weeks, while after two weeks they caused the least reduction percentages.

            After two weeks from treatments of test chemicals Super Masrona oil^® was the most effective one, where it caused reduction percentage (58.2%) followed by CAPL2^® oil (56.1%) without significant differences; but they differ significantly with Diver oil^® (54.3%); and so withAdmire^® (50.4%); Tiger oil^® (49.2%) and Kzoil^® (48.0%) which have not significant differences in between. After four weeks CAPL2 oil^® was the most effective treatment where it caused reduction percentage (77.2%) with significant differences with the two next effective treatments Diver oil^® (73.0%) and Super Masrona oil^® (72.3%). Tiger oil^® caused (68.2%) reduction effect differing significantly with the previous and followed treatments. Kz oil^® caused reduction percentage (65.5%)without significant differences with Admire^® (64.4%). After six weeks of application Tiger oil^® was the most effective treatment followed by Diver oil^®, Super Masrona oil^®, CAPL2 oil^®, Kz oil^® and Admire^® where they caused reduction effects as (78.1%), (73.2%), (70.6%), (70.0%), (68.0%) and (66.3%), respectively. Data Means showed that CAPL2 oil^® was the most effective compound through the experiment where it caused average mean reduction effect (72.9%) followed by Tiger oil^® (71.3%) and Diver oil^® (70.4%) without significant differences in between. Super Masrona oil^® caused reduction effect (69.2%) with significant differences with Kz oil^® (67.4%) and Admire insecticide caused mean reduction effect value (66.6%) without significant differences with Kz oil^®.

B) Effect of tested compounds during fruiting stage

L.S.D_0.05 (Means)= 1.41

Figure 2 : Efficacy of some insecticide; against the citrus red-scale insect Aonidiella aurantii (Maskell) infest orange trees, at Kafr-Eldwar, El-Beheira Governorate, during fruiting stage (2011).

Data in Fig. (2) illustrate the effect of the tested compounds against the citrus red-scale Aonidiella aurantii (Maskell) insect during fruiting stage. Diver oil^® 97% caused the highest reduction effect influence against the tested insect and Kz oil^®95% was the least effective one. Two weeks after treatment Super Masrona oil^® gave the highest reduction effect (70%) followed by CAPL2 oil^® (67.1%) and Diver oil^® (65.2%) without significant differences, but they significantly differed with Admire^® (60%), Tiger oil^® (59.6%) and Kz oil^® (58.1%). After four weeks, Admire^® caused the highest reduction effect (74.3%) without significant differences with CAPL2 oil^® (72.6) and Diver oil^® (72.1%), and significantly differed with Super Masrona oil^® (67.2%), Tiger oil^® (64.3%) and Kz oil^® (61%). After six weeks of application Tiger oil^® was the most effective treatment followed by Diver oil^®, Super Masrona oil^®, CAPL2 oil^®, Kz oil^® and Admire^® where they caused reduction effects as 83%, 78.2%, 74.6%, 74.3%, 72.0% and 58.4% respectively. Diver oil^® was the most effective treatment after eight weeks from application where it caused reduction effect (86%), followed by CAPL2 oil^® (85.4%), Tiger oil^® (84.2%) and Admire^® (82.0%) without significant differences between them while they significantly differed with Super Masrona oil^® (79.1%) and Kz oil^® (77.9%).

            Means of data showed that Diveroil^® was the most effective compound through the experiment where it caused average mean reduction effect(75.3%) followed by CAPL2 oil^®(74.5%) without significant differences in between, and so followed by Super Masrona oil^® and Tiger oil^® with significant differences by mean reduction effect (72.5%) and (72.6%) respectively. Admire insecticide caused mean reduction effect value(68.5%)without significant differences with Kz oil^® which caused mean reduction effect as (67.3%).

            Generally, it could be recommended that, light summer oils gave successful control against armored red-scale insect infesting orange trees in Beheira governorate, where they were more effective and less environmental hazards than the other chemical groups. The obtained results are in agreement with Helmy et al. (1992), Moursi (1996), EI-Deeb (1999), Abdel-Rhaman et al., (2002) El-Deeb et al.,(2002), Mona et al.,(2002)and Abo-Shanab (2005).