Foraging efficiency of Lysiphlebus fabarum Marshall (Hymenoptera: Aphidiidae) parasitizing the black bean aphid, Aphis fabae Scopoli (Hemiptera: Aphididae), under laboratory conditions Majid Mahmoudi, Ahad Sahragard ⁎, Jalal Jalali Sendi Department of Plant Protection, Faculty of Agriculture, the University of Guilan, Rasht, Iran abstract article info Article history: Received 20 June 2009 Revised 10 November 2009 Accepted 22 November 2009 Keywords: Aphis fabae Functional response Mutual interference Lysiphlebus fabarum Sex ratio Foraging efficiency of Lysiphlebus fabarum Marshall, the most abundant and effective parasitoid of the black bean aphid, Aphis fabae Scopoli, in terms of functional and numerical responses and mutual interference, was studied on broad bean plants in a growth chamber at 21 °C, 70 ± 5% RH and a photoperiod of 16:8 (L:D) h. Using logistic regression, a type II functional response was determined for L. fabarum. Nonlinear least-square regression was used to estimate the searching efficiency (a') and handling time (T h ). Numerical response of L. fabarum to cumulative host densities was partially linearly increasing. Nicholson's model and linear regression were used to determine the per capita searching efficiency and interference coefficient, respectively. In general, the per capita parasitism and, consequently, the per capita searching efficiency decreased significantly as parasitoid density increased. Mutual interference and quest constants were -0.508 and -0.697, respectively. The results of this study suggest that both the host and parasitoid densities have no significant impact on the progeny sex ratio. The information provided here will be useful in assessing the efficiency of L. fabarum as a biological control agent of A. fabae, devising mass-rearing protocols and implementing release programs for this parasitoid. © Korean Society of Applied Entomology, Taiwan Entomological Society and Malaysian Plant Protection Society, 2010 Published by Elsevier B.V. All rights reserved. Introduction Aphis fabae Scopoli (Hemiptera: Aphididae) is a polyphagous cosmopolitan pest (Blackman and Eastop, 2000) and one of the best- known pests of agricultural ecosystems, causing damage to horticul- tural plants (Minks and Harrewijn, 1989). Lysiphlebus fabarum is a solitary endoparasitoid and is the most abundant parasitoid of A. fabae in agro-ecosystems (Stary, 1986). This parasitoid has the potential to cause drastic reductions in A. fabae populations and could be useful in the biological control of this pest species (Stary, 1986; Volkl, 1992). The study of parasitoid and predator behavior is an important key to understanding how they influence the population dynamics of their hosts or prey and how they influence the structure of the insect communities in which they live (Jervis and Kidd, 1996). The analysis of functional and numerical responses of parasitoid– host interactions is often used to determine the potential effects of parasitoids on its host population (Oaten and Murdoch, 1975). For parasitoids of many insects, including aphids, a Type II functional response has been determined. For example, a Type II functional response has been recorded in Aphidius smithi on Acyrthosiphon pisum (Mackauer, 1983), Aphidius sonchi on Hyperomyus lactucae (Liu, 1985), Lysiphlebus testaceipes on Aphis gossypii (Bazzochi and Burgio, 2001), A. matricariae and A. colemani on A. gossypii (Zamani et al., 2006), Diaeretiella rapae on Brevicoryne brassicae (Fathipour et al., 2006), Gonatocerus ashmeadi on the glassy-winged sharpshooter, Hormalodisca coagulata (Chen et al., 2006) and A. matricariae on A. fabae (Tahriri et al., 2007). However, a type III functional response has been reported for Trioxys indicus on Aphis craccivora (Singh and Sinha, 1983), A. colemani and L. testaceipes on Shizaphis graminum (Jones et al., 2003) and T. pallidus on Chromaphis juglandicola (Rakhshani et al., 2004). Numerical responses of parasitoids or predators can be explained in terms of the progressive change in the number of their progeny in relation to an increase in host (prey) density (Solomon, 1949). Wright and Laing (1980) found that Hippodamia tredecimpunctata tibialis Say showed a greater numerical response than Coleomagilla maculata lengi Timberlake at high densities of Rhopalosiphum maidis (Fitch) due to greater fecundity. The numerical response of the two lady beetles by oviposition was linear. A similar result was obtained by Uygun and Atlihan (2000) for Scymnus levaillanti at lower density of its prey, A. gossypii. Asgari et al. (2002) found a different response for Trissolcus semistriatus, an egg parasitoid of the Sunn pest. As it was linear when parasitizing Eurygaster integriceps but it was a curvilinear relationship when parasitizing Graphosoma lineatum. However, a curvilinear Journal of Asia-Pacific Entomology 13 (2010) 111–116 ⁎ Corresponding author. Fax: +98 131 6690281. E-mail addresses: sahra1330@yahoo.com, sahragard@guilan.ac.ir (A. Sahragard). 1226-8615/$ – see front matter © Korean Society of Applied Entomology, Taiwan Entomological Society and Malaysian Plant Protection Society, 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.aspen.2009.11.007 Contents lists available at ScienceDirect Journal of Asia-Pacific Entomology journal homepage: www.elsevier.com/locate/jape