Abstract
Scymnus syriacus Marseul is one of the most important biocontrol agents of aphids in citrus orchards. Understanding the efficiency and host specificity of natural enemies can help improve their effectiveness as biological control agents of particular pests. In this study, the functional response, preference and switching behaviour of different stages of S. syriacus feeding on Aphis spiraecola Patch and Aphis gossypii Glover, on orange leaves, were studied under laboratory conditions of 27 ± 2°C, 65 ± 5% RH and a photoperiod of 16L : 8D. The results indicate that 4th instar larvae and adult males and females of this predator exhibit a type II functional response when offered different numbers (3, 5, 7, 10, 20, 30, 40, 60 and 80) of both A.spiraecola and A. gossypii. Adult females had significantly higher attack rates (a) on both species of aphids. Handling times (Th) of adult male predators on A. spiraecola and those of 4th instar larvae on A. gossypii were shorter than that of the other stages. In no-choice preference experiments, adult females fed equally on both species of aphid, but the 4th instar larvae preferred A. gossypii. In switching experiments, prey selection was evaluated by simultaneously presenting different ratios (30 : 50, 40 : 40 and 50 : 30) of the two aphids, A. spiraecola : A. gossypii, to the predator. The 4th instar larvae and adult females of S. syriacus showed higher preference for A. gossypii at each ratio offered (except adult females offered the 50 : 30 ratio). Based on their foraging behaviour 4th instar larvae and adult females of S. syriacus are suitable for use in integrated management of citrus aphids.
Highlights
Citrus is a semi-tropical fruit crop with global availability and a popular component of human diets, which is grown in more than 140 countries (Liu et al, 2012)
It shows that the attack rate (a) of adult females of S. syriacus on A. spiraecola is higher than that of 4th instar larvae and adult males (Table 3)
The results of the current study extend our knowledge on the functional response and prey preference of one of the most important predators of citrus aphids and provide a better understanding of prey-predator interactions
Summary
Citrus is a semi-tropical fruit crop with global availability and a popular component of human diets, which is grown in more than 140 countries (Liu et al, 2012). Adults and immatures of these aphids can cause direct damage, especially to young citrus plantations by feeding on phloem sap. During feeding they inject saliva, which is phytotoxic and adversely affects the physiology of the trees. Growth of sooty mould on aphid honeydew on leaves hinders their photosynthesis (Blackman & Eastop, 2000; Garzo et al, 2002). Both of these species of aphids cause indirect damage by transmitting important viruses (Blackman & Eastop, 2000), such as Citrus tristeza closterovirus (Closterovirus: Closteroviridae) (Ayazpour et al, 2013). Biological control is a safe alternative method for controlling aphids in citrus orchards (Alizadeh Kafeshani et al, 2018)
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