| Pectinophora gossypiella and Spodoptera exigua are the key insect pests of cotton all over the world.Nowadays,biological control of insect pests is thought to be one of the safest management tactics.In biological control strategies,predators are the most effective agents to control insect pests.Among Orius species,the predatory flower bug,Orius strigicollis Poppius(Heteroptera: Anthocoridae),is one of the most active and the best entomophagous predators against different insect pests especially lepidopteran pests.And to the most of current research,the studies regarding the fitness of O.strigicollis using twosex life table tools and its predating potential on P.gossypiella and S.exigua at different temperatures are lacking.Therefore,in the current study,we used two-sex life table tools to evaluate the fitness of O.strigicollis on P.gossypiella and S.exigua eggs,as well as,functional response,feeding potential and prey preference of O.strigicollis on P.gossypiella and S.exigua immature stages at three different temperatures in the laboratory condition(75 ± 5% RH and 16 L:8 D).Furthermore,the fitness and feeding potential of O.strigicollis were determined under the selection pressure on different eggs densities of P.gossypiella and S.exigua.1)Functional response parameters,feeding potential and prey preference of O.strigicollisIn this study,to evaluate the pest control potential of O.strigicollis predation functional response,feeding potential and prey preferences were determined in laboratory at three different temperatures(24 °C,28 °C and 32 °C).The type and parameters of female predator functional response were determined by using logistic regression analysis and Holling's disc equation.The results showed a type II functional response when O.strigicollis fed on both prey species eggs at each temperature.The results suggested that O.strigicollis exhibited suitable efficacy on eggs of S.exigua than that of P.gossypiella,however O.strigicollis acted more effectively at 28 °C than the other tested temperatures in laboratory conditions(75 ± 5% RH and 16 L:8 D)considering higher consumption rate(with S.exigua eggs= 18.63;with P.gossypiella eggs= 14.04),shorter handling time(with S.exigua eggs= 1.29 h;with P.gossypiella eggs= 1.71 h)and higher attack rate(with S.exigua eggs= 0.05 h-1;with P.gossypiella eggs= 0.06 h-1).At each temperature,as prey density increased,total searching time and efficiency was decreased while the handling time increased.In addition,O.strigicollis prefers to feed on eggs compared to first instar larvae of both prey species at each temperature.All predatory stages consumed the highest number of both prey species eggs and first instar larvae at 28 °C.We found that,O.strigicollis was efficient in controlling first instar larvae of P.gossypiella than that of S.exigua at adult stage compared to other predatory stages at each temperature.2)Using an age-stage,two-sex life tables to determine fitness traits of Orius strigicollis at three different temperaturesThis study explains the age-stage,two-sex life table traits of O.strigicollis on P.gossypiella and S.exigua eggs at different temperatures(24,28 and 32 °C)in laboratory.The egg development period was minimum at 32 °C(with P.gossypiella eggs= 2.87 ± 0.04 d and with S.exigua eggs= 2.81 ± 0.04)than other two tested temperatures.The mean survival time of male was higher at 24 °C(7.50 ± 0.29 d)on P.gossypiella eggs,whereas it was higher on S.exigua eggs at 28 °C(9.00 ± 0.36 d)and the mean survival time of female was higher at 28 °C(with P.gossypiella eggs= 8.88 ± 2.13 d and with S.exigua eggs= 10.58 ± 0.46 d)than other two tested temperatures.The APOP(adults preoviposition period)of adult females were significantly shorter at 32 °C(with P.gossypiella eggs= 0.11 ± 0.08 d and with S.exigua eggs= 0.28 ± 0.08 d)than other two tested temperatures.While,the oviposition period of O.strigicollis was significantly longer at 28 °C(with P.gossypiella eggs= 7.88 ± 1.92 d and with S.exigua eggs= 9.40 ± 0.40 d)than other two tested temperatures.Similarly,the fecundity of O.strigicollis was recorded highest at 28 °C(with P.gossypiella eggs= 66.12 eggs/female and with S.exigua eggs= 96.51 eggs/female)than other two tested temperatures.There were significant differences in the intrinsic rate of increase(r)and finite rate of increase(?)of O.strigicollis on both prey species at three temperatures.The value of intrinsic rate of increase(r)was higher at 28 °C(with P.gossypiella eggs= 0.14 d-1 and with S.exigua eggs= 0.17 d-1)than other two tested temperatures.Similarly,the value of finite rate of increase(?)was higher at 28 °C(with P.gossypiella eggs= 1.15 ± 0.02 d-1 and with S.exigua eggs= 1.18 ± 0.01 d-1)than other two tested temperatures.The net reproductive rate(R0)was the highest at 28 °C(with P.gossypiella eggs= 17.63 offspring and with S.exigua eggs= 41.50 offspring)than other two tested temperatures.Conversely,the mean generation time(T)was significantly different and the highest at 24 °C(with P.gossypiella eggs= 23.79 days and with S.exigua eggs= 27.71 days)than other two temperatures.Gross reproductive rate(GRR)was significantly different and the highest at 28 °C(with P.gossypiella eggs= 90.32 and with S.exigua eggs= 82.63)than other two temperatures.This study concluded that maximum survival and growth capacity of O.strigicollis could be attained at 28 °C when fed on P.gossypiella and S.exigua eggs.3)Feeding capacity and fitness of Orius strigicollis under selection pressureIn this study,different prey densities(P.gossypiella eggs= 5,10,and 15 and S.exigua eggs= 10,15,and 20)were used to calculate the feeding capacity and fitness of O.strigicollis in the laboratory at 28 °C ± 1,75 ± 5 % RH and 16:8(L:D).The results showed that the adult females of O.strigicollis consumed significantly more eggs(188.33)than males(117)when 15 eggs of P.gossypiella were given than those other preying densities.Similarly,the adult females of O.strigicollis consumed significantly more eggs(140.09)than males(118.54)when 20 eggs of S.exigua were given than those other preying densities.The results of life table parameters showed that,maximum growth capacity of the predatory bug O.strigicollis was attained when it was fed on 10 and 15 eggs of P.gossypiella(r= 0.14 ± 0.01 d-1 and 0.14 ± 0.01 d-1,respectively,and ?= 1.15 ± 0.01 d-1 and 1.15 ± 0.02 d-1,respectively)and 20 eggs of S.exigua(r= 0.17 ± 0.01 d-1 and ?= 1.19 ± 0.01 d-1).Furthermore,shorter development period was also observed in the case of 15 eggs of P.gossypiella and 20 eggs of S.exigua.In addition,the results of feeding potential suggest that,the predatory stages of O.strigicollis has considerable predatory potential and prefers feeding on eggs of P.gossypiella and S.exigua than on their first instar larvae.Furthermore,the adults of O.strigicollis feed more on P.gossypiella first instar larvae than S.exigua first instar larvae.In conclusion,O.strigicollis can be used as a potential biological control agent against the P.gossypiella and S.exigua.Studies on fitness of O.strigicollis under selection pressure of two different prey species can be used for optimizing mass rearing when feeding on P.gossypiella and S.exigua eggs. |
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