ORIGINAL PAPER Differential responses of midgut soluble aminopeptidases of Helicoverpa armigera to feeding on various host and non-host plant diets Purushottam R. Lomate • Vandana K. Hivrale Received: 29 July 2010 / Accepted: 7 June 2011 / Published online: 1 July 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Differential responses of midgut soluble ami- nopeptidases were studied in Helicoverpa armigera larvae fed on various host (chickpea and pigeon pea) and non-host (bitter gourd and chili) plant diets. Larval growth was significantly reduced by non-host plant diets. Although the serine proteinase activities were inhibited, aminopeptidase activities were significantly increased in the larvae fed on non-host plant diets. Results were qualitatively and quan- titatively confirmed with in vivo and in vitro analyses. It was noted that aminopeptidases had given more preference to ApNA than LpNA on non-host plant diets and vice versa on host plant diets. However, optimum pH for aminopep- tidase activity (around pH 7.0–8.0) and susceptibility to inhibitors was similar in the larvae fed on host as well as non-host plant diets. These results suggest that H. armigera regulates digestive enzyme levels to obtain better nour- ishment from the diet and avoid toxicity due to nutritional imbalance. A detailed biochemical and molecular analysis of gut aminopeptidases upon exposure of the insect to a particular diet will highlight their specific roles. Keywords Diet Á Helicoverpa armigera Á Midgut aminopeptidase Á Nutrition Á Serine proteinases Introduction Helicoverpa armigera (Hu ¨bner) (Lepidoptera: Noctuidae) is a polyphagous and devastating pest of many important crop plants and responsible for heavy economical losses to agriculture. It infests more than 300 plant species throughout the world (Rajapakse and Walter 2007). Polyphagy, high mobility, fecundity, and facultative dia- pause are the key physiological characteristics that facili- tate survival of H. armigera even in adverse habitats (Fitt 1989). Conventional approaches have failed to control this pest because it has developed resistance against many insecticides (Kranthi et al. 2002). While developing the methods of insect control, it is important to have complete understanding of the target insect physiology and midgut biochemistry (Kazzazi et al. 2005). Many studies have been carried out on the interactions of H. armigera gut serine proteinases and plant proteinase inhibitors with the objective of identifying potential inhibitors of insect proteinases (Giri et al. 1998, 2003; Chougule et al. 2005; Damle et al. 2005; Srinivasan et al. 2005; Tamhane et al. 2007). A study revealed that the seeds of bitter gourd contain two major proteins (BGPI-1 and -2) and two minor proteins (BGPI-3 and -4) having inhibitory activity against both trypsin and H. armigera gut proteinase (HGP) (Telang et al. 2003). Two proteinase inhibitors (CapA1 and CapA2) from Capsicum annum were also identified and these inhibitors showed potency against HGP (Tamhane et al. 2005). Plant proteinase inhibitors have been shown to reduce the growth rates in larvae of numerous insect species (Hilder et al. 1987; Duan et al. 1996). In most cases, the effects of plant proteinase inhibitors are transient, because insects can adapt to pro- teinase inhibitors by over expressing proteinase inhibitor- insensitive proteinases, by regulating the level of existing Handling Editor: Guy Smagghe. Electronic supplementary material The online version of this article (doi:10.1007/s11829-011-9140-9) contains supplementary material, which is available to authorized users. P. R. Lomate Á V. K. Hivrale (&) Department of Biochemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431004, Maharashtra, India e-mail: vkhbiochem@gmail.com 123 Arthropod-Plant Interactions (2011) 5:359–368 DOI 10.1007/s11829-011-9140-9