Comparison of growth parameters of the predator, Chrysoperla nipponensis-B (Neuroptera: Chrysopidae) reared on a diet of eggs of Corcyra cephalonica (Lepidoptera: Pyralidae) and an artificial diet containing ginger

The growth parameters of the green lacewing, Chrysoperla nipponensis-B (Okamoto), were studied under laboratory conditions. The highest mortality was recorded in the immature stages (instars 1st, 2nd, 3rd and pupae) of C. nipponensis fed on the eggs of Corcyra cephalonica (37.26%). The sex ratios (proportion of female to male) when reared on the eggs of C. cephalonica and an artifi cial diet with ginger were 0.93 : 1.00 and 0.87 : 1.00, respectively. The maximum life spans of females reared on the eggs of C. cephalonica and an artifi cial diet with ginger were 63 and 64 days, respectively. The females reared on the eggs of C. cephalonica produced the highest number of eggs (10.4) on the fi fth day of oviposition, whereas on the artifi cial diet with ginger it was 9.26 on the eighth day of oviposition. The net reproductive rate (Ro) and maximum gross reproductive rate (GRR) of C. nipponensis fed on the eggs of C. cephalonica were 69.50 and 223.10 females per female per generation, respectively, whereas for the artifi cial diet with ginger they were 117.24 and 236.89 females per female per generation, respectively. Mean generation time (T) was 37.06 and 48.16 for the eggs of C. cephalonica and artifi cial diet with ginger, respectively. The intrinsic rate of natural increase (r) was 0.11 and 0.09 females per female per day for the eggs of C. cephalonica and artifi cial diet with ginger, respectively. The fi nite rate of increase (λ) was 1.12 and 1.11 females per female per day for the eggs of C. cephalonica and artifi cial diet with ginger, respectively. The population doubling time (DT) was 6.05 days on the diet of eggs of C. cephalonica and 7.00 on the artifi cial diet with ginger.


INTRODUCTION
Green lacewings are important predatory biological control agents that can be used in biological control programs (Gautam, 1994;Venkatsan et al., 2008). Chrysoperla (carnea-group) and Mallada desjardinsi (Navas) are well recognized and widely distributed green lacewing species in India, Europe, USSR, North America, South America and Central Africa. The green lacewings, Chrysoperla spp. (Neuroptera: Chrysopidae) are cosmopolitan predators that occur in a wide range of agricultural habitats. The larvae of Chrysoperla spp. are voracious and effi cient biological control agents of various phytophagous arthropods such as aphids, caterpillars, leafhoppers, whitefl ies, thrips and insect eggs (McEwen et al., 2001;Carrillo & Elanov, 2004). It is estimated that up to one third of the successful biological insect pest control programs are attributed to the Eur. J. Entomol. 113: 387-392, 2016 doi: 10.14411/eje.2016.049

ORIGINAL ARTICLE
trays to prevent cannibalism. The larvae of the different cohorts of eggs were fed either frozen eggs of C. cephalonica or the artifi cial diet with ginger. The diets were changed every two days, when 1.5 g of both diets were provided. Daily records of the survival and development of the larvae were kept until the adults emerged. After the emergence of the adults, they were transferred to an oviposition cage and provided with a standard adult diet. The fecundity and mortality were recorded daily until the last adult died. Construction of the life table was done following the procedures described by Birch (1948) and Southwood (1978).
The life table and fecundity schedule were constructed using the following parameters: Life RM%: Percentage of real mortality calculated based on the population density at the beginning of the generation. RM = (dx / lo) 100. IM%: Indispensable (irreplaceable) mortality, which is the portion of generation mortality that would not occur if the apparent mortality (qx) of an age interval was removed from the life system. It is assumed that the subsequent mortality factors will destroy the same percentage of the population independent of any change in population density.
Fecundity schedule X: The pivotal age for the age class in units of time (days). lx: The number of females surviving at the beginning of age class x (given as a fraction of 1.0). mx: The number of female eggs laid by age class x. lxmx: Total number of female eggs laid by age class x. Ro: Net reproductive rate. It is equal to the sum of lxmx or Ro = Σ lxmx.
T: Cohort generation time (in days), approximated by T = Σ Xlxmx / Σlxmx. r: Innate capacity for increase, calculated using rc = ln Ro/Tc. rm: The maximum population growth, the innate capacity for increase, calculated by iteration of Euler's equation, Σe-r.x lxmx.
λ: Finite rate of increase, number of female offspring per female per day, calculated using, λ = er.
DT: Doubling time, the number of days required by a population to double, calculated using, DT = ln2 / r. b: Intrinsic birth rate, 1 / Σe -r.xIx. d: Intrinsic death rate, b -rm. GRR: Gross reproduction rate calculated using Σmx. The population parameters of the life and fecundity tables were constructed separately for C. nipponensis reared on both diets based on 3 cohorts for each diet. Moreover, comparison between life parameters of C. nipponensis reared on the diet with ginger and the eggs of C. cephalonica were statistically compared using Student t-test and presented as Mean ± SE. There are several studies on the life table parameters of Chrysoperla spp. reared on natural prey as life tables are one of the most important tools in entomological research (Win et al., 2009). Cohort life table provide a comprehensive description of the survivorship, development and reproduction of a population, which are fundamental factors in both theoretical and applied population ecology (Taghizadeh et al., 2008). Moreover, there are no comparative life table studies of C. nipponensis reared on different diets in Malaysia. Therefore, this study was conducted to determine the growth parameters of C. nipponensis reared on the eggs of Corcyra cephalonica and an artifi cial diet that included ginger, with the view of improving the mass and quality production of C. nipponensis for use against insect pests.

Rearing of C. nipponensis on the eggs of Corcyra cephalonica
Chrysoperla nipponensis adults were reared in rectangular cages 37 × 28 × 22 cm in size. Adults were supplied with an artifi cial standard diet consisting of yeast, sugar, honey, casein and distilled water. Wet cotton was provided in glass vials as a source of water. For the oviposition of females, a black organza cloth was placed on top of the cage and the eggs deposited on this cloth were removed daily. The larvae from the eggs were then reared on the eggs of Corcyra cephalonica. The eggs of C. cephalonica were spread on a sterilized mixture of maize, rice, wheat and semolina (1 : 1 : 1 : 1) on which they developed up to the adult stage and were then collected for mating in a plastic cage. The eggs laid by these adults were then collected and killed by placing them in a freezer before being used to rear C. nipponensis larvae.

Composition of the artifi cial diet for larvae
The artifi cial diet for the larvae consisted of 100 g ground beef (with 25% fat), 100 g ground beef liver, 15 g sucrose, 100 g hen eggs, 10 ml distilled water, 20 g honey (5 g dissolved in 15 ml of water), 14 g brewer's yeast, 5 ml acetic acid, 0.5 g potassium sorbate, 0.5g ginger and 5 ml vitamin solution. All the ingredients used were weighed carefully using a Digital Analytical Balance (Sartorious, BT-224S, Germany). The ground beef and ground beef liver were cut into small pieces using a knife and were kept in a refrigerator for 24 h. The mixture of meat, honey, water, ginger and brewer's yeast were blended in a food processor (Panasonic, MK-5087M, Japan). In a beaker, 20 ml of water was heated to 80 to 90°C on a hot plate (IKA-COMBIMAG RCT 31197, China) and 15 g sucrose, 5 ml of acetic acid and potassium sorbate were added and stirred using a magnetic stirrer. Then, 100 g of blended eggs were added. All ingredients were blended (BRAUN, ZK-200, Germany) for 5 to 6 min until the entire mixture had a stringy paste-like consistency. The diet was then fed to the larvae in trays that are used in ELISA tests.

Life table experiments
The life table of C. nipponensis was constructed using data obtained when the larvae were fed C. cephalonica eggs and the above artifi cial diet at 25 ± 2°C, 55-85% RH and a 12L : 12D photoperiod. Three separate groups of 148 (cohort 1), 123 (cohort 2) and 106 (cohort 3) freshly laid eggs of C. nipponensis, were used to construct life tables for individuals reared on these two diets. The eggs were placed individually in the cells of ELISA lonica and an artifi cial diet with ginger. Fig. 1 indicates that during the life span of the predator, there was a high mortality of those reared on the eggs of C. cephalonica during the egg, 2 nd instar larval and pupal stages. However, those reared on the artifi cial diet with ginger suffered a high mortality during the egg, 1 st instar larval and pupal stages. Green lacewings are highly sensitive to changes in temperature and water availability, which affects the growth and survival of these predators (Schowalter, 2006). The fi rst emergence of adults reared on eggs of C. cephalonica and artifi cial diets with ginger occurred on day 21, 22 and 22, and day 26, 24 and 24 for cohorts 1, 2, and 3, respectively. The maximum life span of C. nipponensis reared on artifi cial diet with ginger and eggs of C. cephalonica were recorded at 88 and 85 days, respectively. The survivorship curves are of type III based on the classifi cation of Pearl (1928), Speight et al. (1999) and Schowalter (2006).

Mortality of immature stages of C. nipponensis
The age specifi c mortality of the immature stages of C. nipponensis, reared on eggs of C. cephalonica and the artifi cial diet with ginger is shown in Table 1. All larvae underwent three larval molts before transforming into pupae. The highest mortality of C. nipponensis reared on both diets were recorded in the pupal (19.08 and 6.64, respectively) followed by 2 nd instar larval stage (7.39 and 3.89,  respectively). Overall, the total mortality in the immature stages (1 st , 2 nd , 3 rd and pupae) of C. nipponensis reared on eggs of C. cephalonica was 37.26%, which is higher than that recorded on the artifi cial diet with ginger (21.62%). The total number of adults that emerged from the artifi cial diet with ginger was higher (118 females : 134 males) than emerged from those reared on eggs of C. cephalonica (103 females : 109 males). The female to male sex ratio recorded for the artifi cial diet with ginger was 0.87 : 1.00 and that for those reared on eggs of C. cephalonica was 0.93 : 1.00. Studies on another lacewing species, Mallada bioninensis (Okamoto) also indicate a signifi cant effect of diet on the mortality of the different stages (Shivankar & Singh, 1998;Nehrae et al., 2004;Elsiddig et al., 2006). The high mortality of the immature stages of various species of lacewings is also reported by Alasady et al. (2010) for Apertochrysa sp. and Gautam et al. (2009) for Chrysoperla sp. and Mallada desjardinsi (Navas).

Age-specifi c fertility schedule
Age-specifi c survivorship (l x ) and fecundity (m x ) of C. nipponensis are shown in Figs 2 and 3. For those reared on the artifi cial diet with ginger and eggs of C. cephalonica, the fi rst adult female emerged on day 25 and 21, whereas, the death of last female reared on artifi cial diet with ginger and eggs of C. cephalonica was recorded on day 88 and 85, respectively. The maximum life span of females reared on eggs of C. cephalonica and an artifi cial diet with ginger were 63 and 64 days, respectively that is similar to that reported in several previous studies, which show that the longevity of lacewings depends on the food available to the adults and the diet the larval stages were fed on (Joshi & Yadav, 1990;Nehrae et al., 2004;Senthil Kumar & Gautam, 2007). Females reared on the artifi cial diet with ginger started egg laying on day 30, or 5 days after emergence, whereas those reared on eggs of C. cephalonica, started laying eggs on day 26, or 5 days after emergence. The highest number of eggs produced per female reared on the artifi cial diet with ginger was 9.26 on the fourth day of oviposition, whereas on the eggs of C. cephalonica, it was 10.4 on the fi fth day of oviposition. Insect fecundity and life span are both infl uenced by the quality of the food (Siswanto et al., 2008). Table 2 summarizes the population and reproductive parameters of C. nipponensis. Maximum mean generation time (T) of the individuals reared on the artifi cial diet with ginger was 42.19 ± 0.12 days compared to the 37.06 ± 0.15 days for those reared on eggs of C. cephalonica. The intrinsic rate of natural increase (r) recorded for those reared on the artifi cial diet with ginger was 0.11 ± 0.01 and on the eggs of C. cephalonica (natural) 0.12 ± 0.01 females per female per day. Jervis et al. (2005) also report that prey species can infl uence the intrinsic rate of natural  increase of predators. The fi nite rates of increase (λ) for those reared on the artifi cial diet with ginger and eggs of C. cephalonica were 1.11 ± 0.02 and 1.12 ± 0.02 females per female per day, respectively. These results are in accordance with Jokar et al. (2012) who record a fi nite rate of increase (λ) of 1.17 ± 0.001 and 1.20 ± 0.002 for C. carnea fed on Anagasta kuehniella and a semi-artifi cial diet, respectively. The doubling time (DT) of the predator reared on the eggs of C. cephalonica was 6.05 ± 0.02 days, which is less than when reared on the artifi cial diet with ginger (7.00 ± 0.03 days). Studies show that r, T, and DT are useful indices of population growth of insects under a given set of conditions (Siswanto et al., 2008). Moreover, C. nipponensis reared on the eggs of C. cephalonica had a lower reproductive performance than those reared on the articial diet with ginger. The superior performance of the C. nipponensis reared on the artifi cial diet with ginger in terms of several biological parameters may be due to the addition of ginger that not only enhances its active predatory period but also its searching and killing abilities. Natural alternatives to antibiotics, such as ginger, has attracted attention due to its wide range of potential benefi cial effects (Manesh et al., 2012). Ginger is used in the preparation of food to impart fl avour, colour and food preservation, and also enhances palatability (Polasa & Nirmala, 2003). The net reproductive rate (Ro) was higher on the artifi cial diet with ginger (117.24 ± 0.90 females per female per generation) than on the eggs of C. cephalonica (69.50 ± 0.82 females per female per generation). The maximum gross reproductive rate (GRR) was 236.89 ± 1.53 and 223.10 ± 1.4 females per female per generation for those reared on the artifi cial diet with ginger and eggs of C. cephalonica, respectively. The results are similar to those of Jokar & Zarabi (2012) who record a GRR of 225.5 ± 3.45 and 267.8 ± 4.8 for C. carnea fed A. kuehniella and a semi artifi cial diet, respectively.

CONCLUSIONS
This life table study indicates that the survivorship curves of C. nipponensis fed on both the eggs of C. cephalonicaa and an artifi cial diet with ginger is of type III, which is commonly found in insects. The highest mortality of C. nipponensis was recorded in the immature stages (1 st , 2 nd , 3 rd and pupae), which are the weakest stages in its life cycle. Rearing C. nipponensis on an artifi cial diet with ginger resulted in the largest number of individuals reaching the adult stage. Higher survival and reproductive potential were recorded for C. nipponensis reared on the artifi cial diet with ginger than on the eggs of C. cephalonica. Population parameters (GRR, Ro, and T) were also higher on the artifi cial diet ginger except for the fi nite rate of increase that was same on both diets. The doubling time (DT) was one day longer on the artifi cial diet with ginger than on the eggs of C. cephalonica. Thus an artifi cial diet with ginger is more suitable for the mass rearing of C. nipponensis than the eggs of C. cephalonica, and has an additional advantage of an increased shelf life due to the inclusion of ginger in the diet.