Life table parameters of the cotton bollworm, Helicoverpa armigera (Lep.: Noctuidae) on different soybean cultivars

Influence of 13 soybean cultivars (356, M4, M7, M9, Clark, Sahar, JK, BP, Williams, L17, Zane, Gorgan3 and DPX) on the life table parameters of the cotton bollworm, Helicoverpa armigera (Hübner) was studied at 25 ± 1°C, relative humidity of 65 ± 5% and a photoperiod of 16: 8 (L: D) h. The survival rate (lx) of individuals developed to adults from the initial cohort on the mentioned cultivars was estimated 0.87, 0.83, 0.96, 0.96, 0.77, 0.72, 0.81, 0.72, 0.85, 0.74, 0.85, 0.88 and 0.72, respectively. The longest and shortest life expectancy (ex) of the pest was 44.22 and 35.98 days on Gorgan3 and BP, respectively at the beginning of life. The intrinsic rate of natural increase (rm) on different cultivars ranged from 0.1324 to 0.1848 (day ), which was lowest on 356 and highest on M9. The highest net reproductive rate (R0) was on M7 (354.92 female/female/generation) and the lowest value of this parameter was on 356 (89.35). The values of finite rate of increase (ë), mean generation time (T) and doubling time (DT) on different soybean cultivars were as follows: 1.14 to 1.20 female offspring per female per day for ë, 28.85 to 36.61 days for T and 3.75 to 5.23 days for DT. Because of the higher coefficient of determination (R) value in Gompertz model, data from different cultivars had a better fit to this model compared with Weibull model. The results indicated that 356, L17, Gorgan3, BP and Sahar cultivars were less suitable host plants, suggesting that they are more resistant to H. armigera than the other cultivars. Key words: Helicoverpa armigera, intrinsic rate of natural increase, life table, soybean cultivars ƵŶǀĪģ ţ Ő źǀŧ ÎÐ Śƿƺos ƮoƣŹ 356  M4  M7  M9  Clark  Sahar  JK  BP  Williams  L17  Zane  Gorgan3 ƹ DPX ƵŻƺƛ ƭźĩ ƾĭŶƳŻ ƩƹŶū ƽŚƷźŤƯřŹŚě ƽƹŹ ƽ ƶŞƴě  Helicoverpa armigera (Hübner)  ƽŚƯŵ Źŵ Î ± ÏÒ ƶūŹŵ ƽ ŽƺǀƀƬs  ƾŞƀƳ ŢŝƺƏŹ Ò ± ÓÒ ƵŹƹŵ ƹ ŶƇŹŵ ƽ ƽŹƺƳ ÎÓ ƾƿŚƴƃƹŹ ŢƗŚs ƹ Õ ƾĪƿŹŚţ ŢƗŚs Ŷƃ ƲǀǀƘţ ŌŚƤŝ űźƳ (lx) ƱŚƯŻ Źŵ ŵřźƟř ƮƷ ŢǀƘưū ŵƹŹƹ ƶƬůźƯ ƶŝ ƶǀƫƹř Ʋs ƽ ƵźƄů ƽ ƶŝ ơƺƟ ƭŚƣŹř ƽƹŹ ƪƯŚĩ Ŝǀţźţ ÕÔ Í  ÕÐ Í  ÖÓ Í  ÖÓ Í  ÔÔ Í  ÔÏ Í  ÕÎ Í  ÔÏ Í  ÕÒ Í  ÔÑ Í  ÕÒ Í  ÕÕ Í ƹ ÔÏ Í ŵƺŝ ƾƳLJƺƏ ƵŚţƺĩ ƹ Ʋƿźţ ƾĭŶƳŻ ƶŝ ŶǀƯř Ʋƿźţ (ex) ƛō Źŵ ƶoŝ ŢoƟō ƾĭŶƳŻ ŻŚ Ŝoǀţźţ ÏÏ ÑÑ ƹ ÖÕ ÐÒ ƭŚƣŹř ƽƹŹ ŻƹŹ Gorgan3 ƹ BP ŵƺŝ ŢoǀƘưū ƂƿřżƟř ƾţřŷ űźƳ (rm) Żř ƞoƬŤŴƯ ƭŚoƣŹř ƽƹŹ ÎÐÏÑ Í Śoţ ÎÕÑÕ Í Ʈĩ ƶĩ ŵƺŝ ƱŚsƺƳ Źŵ Ƃǀŝ ƹ Ʋƿźţ ƶŝ Ʊō ŹřŶƤƯ Ʋƿźţ ƭŚƣŹř ƽƹŹ Ŝǀţźţ 356 ƹ M9 Ŷƃ ƵŶƷŚƄƯ űźoƳ ŹřŶoƤƯ ƲƿźŤƄǀŝ ƪŨƯ Ŷǀƫƺţ ƆƫŚų (R0) ƽƹŹ M7 ÖÏ ÐÒÑ ƵŵŚƯ ƵŵŚƯ ƪƀƳ Ʈĩ ƹ ƽƹŹ Ʊō ŹřŶƤƯ Ʋƿźţ 356 ÐÒ ÕÖ ŵƺŝ ƾƷŚoƴŤƯ űźƳ źƿŵŚƤƯ ƂƿřżƟř (ë) ƪƀƳ Ĩƿ ƱŚƯŻ ƎsƺŤƯ  (T) ƹŵ ƱŚƯŻ šŶƯ ƹ źŝřźŝ ŢǀƘưū ƱŶƃ (DT) ƶŝ Śƿƺs ƞƬŤŴƯ ƭŚƣŹř ƽƹŹ šŹŚoŞƗ Ŝǀţźţ Żř ŶƳŵƺŝ ÎÑ Î Śţ ÏÍ Î ƽřźŝ ŻƹŹ źƷ Źŵ ƵŵŚƯ źƷ ƽřŻř ƶŝ ƵŵŚƯ ë  ÕÒ ÏÕ Śţ ÓÎ ÐÓ ƽřźŝ ŻƹŹ T ƹ ÔÒ Ð Śţ ÏÐ Ò ƽřźŝ ŻƹŹ DT źţLJŚŝ ƪǀƫŵ ƶŝ ƲǀǀŞţ ŜƿźƋ ŹřŶƤƯ Ʊŵƺŝ (R) ƩŶƯ Źŵ Gompertz Ƶŵřŵ  ƶŝ ƽŚƷ Ţsŵ Śoŝ ƽźoŤƸŝ ƁŻřźŝ ƞƬŤŴƯ ƭŚƣŹř ƽƹŹ ƵŶƯō ƩŶoƯ Śŝ ƶƀƿŚƤƯ Źŵ ƩŶƯ Ʋƿř Weibull ŶƴŤoƃřŵ ƭŚoƣŹř ƶoĩ ŵřŵ ƱŚƄoƳ ŪƿŚoŤƳ 356  L17  Gorgan3  BP ƹ Sahar oŝ ƱřƺoƴƗ ƶ ŜsŚƴƯŚƳ źŝřźŝ Źŵ ƽźŤƄǀŝ ŢƯƹŚƤƯ ƭŚƣŹř źƿŚs ƶŝ ŢŞƀƳ ƹ Ƶŵƺŝ ŢƟō ƱŚŝżǀƯ ƱŚƷŚǀĭ Ʋƿźţ H. armigera ŶƴŤƃřŵ ƽŶǀƬĩ ƱŚĭĥřƹ Helicoverpa armigera  Śƿƺs ƭŚƣŹř ƾĭŶƳŻ ƩƹŶū ƾƘǀŞƏ ƂƿřżƟř ƾţřŷ űźƳ 26 Naseri et al.: Life table parameters of the cotton bollworm … Introduction The cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a common insect pest of numerous crops in Iran (Farid, 1986), and is one of the dominant pests of soybean (Kogan & Herzog, 1980). The cotton bollworm can feed on most plant structures including stems, leaves, flower heads and fruits at different development stages (Moral Garcia, 2006). The population of H. armigera has been increased enormously in the soybeanproducing areas especially in the Moghan region, northwest of Iran. Despite high level of natural mortality, this species needs to be controlled by synthetic pesticides (Fitt, 1994). This usage of pesticides is of environmental concern and has repeatedly led to the development of pesticide resistance in H. armigera, especially to the synthetic pyrethroids (Gunning et al., 1984). Consequently, there is considerable interest in alternative management tactics, which might be applied in area-wide or more restricted basis (Naseri et al., 2009). Host plant resistance has been used effectively in sustainable integrated management programs for several crop pests. Plants with antibiosis machanism may reduce insect survival, size or weight, longevity, and reproduction in new generation adults, or they may have an indirect effect by increasing the exposure of the insect to its natural enemies as a result of prolonged developmental time (Dent, 2000; Sarfraz et al., 2006). Host plant resistance is an important tool in terms of being both economically and environmentally acceptable (Kennedy et al., 1987). Population parameters are important in measurement of population growth capacity of species under specified conditions. These parameters are also used as indices of population growth rates responding to selected conditions and as bioclimatic indices in assessing the potential of a pest population growth in a new area (Southwood & Henderson, 2000). Life table is an appropriate tool to study the dynamics of animal populations, especially arthropods, because this tool can provide very important demographic parameters (Maia et al., 2000). Demographic studies have several applications: analyzing population stability and structure, estimating extinction probabilities, predicting life history evolution, predicting outbreak in pest species, and examining the dynamics of colonizing or invading species (Vargas et al., 1997; Haghani et al., 2006). Demographic information may also be useful in constructing population models (Carey, 1993) and understanding interactions with other insect pests and natural enemies (Omer et al., 1996). The cohort life table gives the most comprehensive description of the survivorship, development and reproduction of a population Journal of Entomological Society of Iran, 2009, 29(1) 27 that are fundamental factors in both theoretical and applied population ecology (Taghizadeh et al., 2008). The life table parameters, particularly the intrinsic rate of natural increase (rm), are the most important parameters that can be used to evaluate the level of plant resistance to insects (Razmjou et al., 2006). Host plants displaying lower values of rm are relatively more resistant than the plants with higher values of rm. In the present study, the life table parameters, especially the rm, are used to compare the potential population growth of H. armigera on different soybean cultivars. Models of population dynamics play a central role in understanding the effects of disturbance in both natural and managed ecosystems. One of the most persistent and pervasive disturbances is the widespread use of resistant plants. Of the variety of mortality models are found in the literature, the Gompertz model is the most widely used one (Preston et al., 2001). Knowledge of cultivar susceptibility or resistance and the life table parameters of a pest might be fundamental components of an integrated pest management program for any crops. Such information can aid in detecting and monitoring pest infestations, cultivar selection, and crop breeding (Razmjou et al., 2006). There was little information on the life table parameters of H. armigera on different soybean cultivars, although most related studies have been conducted on the effects of host plants apart from soybean cultivars on life table parameters of H. armigera (Patal & Koshyia, 1997; Liu et al., 2004; Reddy et al., 2004). Therefore, the present study provides novel information on the life table parameters of H. armigera on different soybean cultivars. The goal of this research was to determine the life table parameters of H. armigera on the 13 soybean cultivars, to evaluate susceptibility or resistance of soybean cultivars. Furthermore, our findings on resistant cultivars may be applied to design a comprehensive schem for IPM program of H. armigera. Materials and methods Plant source Seeds of the 13 soybean (Glycine max (L.) Merrill) cultivars including 356 (Delsoy4210), M4, M7, M9, Clark, Sahar, JK, BP, Williams, L17, Zane, Gorgan3 and DPX were obtained from Plant and Seed Modification Research Institute (Karaj, Iran) and were planted in the research field of Tarbiat Modares University in the suburbs of Tehran, Iran in 28 Naseri et al.: Life table parameters of the cotton bollworm … 2007. For this study, the leaves and pods of different soybean cultivars were transferred to a growth chamber at 25 ± 1°C, relative humidity of 65 ± 5% and a photoperiod of 16: 8 (L: D) h. The leaves and pods were used for feeding of 1 and 2 to 5 larval instars, respectively. Laboratory cultures The specimens H. armigera were originally collected from cotton fields in Moghan region located in northwest of Iran in July 2007. The stock culture initiated on an artificial diet (cowpea powder 205 gr, powdered agar 14 gr, ascorbic acid 3.5 gr, sorbic acid 1.1 gr, methyl-p-hydroxybenzoate 2.2 gr, yeast 35 gr, wheat germ powder 30 gr, formaldehyde 37% 2.5 ml, vegetable oil 5 ml and distilled water 650 ml) (Naseri et al., 2009). The insects tested on different soybean cultivars had already been reared for two generations on the same cultivars. The colony was supplemented, from time to time, with larvae collected from field to reduce any inbreeding effects and maintain the vigor of the colony. All experimental insects were kept inside a growth chamber at 25 ± 1°C, relative humidity of 65 ± 5% and a photoperiod of 16: 8 (L: D) h. Experiments Adult moths emerged from the larvae reared on different soybean cultivars were used in the experiments. In order to obtain the same aged eggs of the pest, 10-15 pairs of both sexes of the moth reared on related cultivars were kept inside oviposition container (14 cm in diameter by 19 cm in height), which were sealed at the top with a fine mesh net. After 72 h, the eggs laid w