Philippine Journal of Science 133 (2): 109-114, December 2004 ISSN 0031 - 7683

Reproductive Potential of Ichneumonid , Eriborus argenteopilosus Cameron (:) Reared on Second Instar Cotton Bollworm, Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) Larvae

Leonardo T. Pascua*1 and Miriam E. Pascua2

1Cotton Research Center Cotton Development Administration, Batac, Ilocos Norte 2College of Agriculture and Forestry Mariano Marcos State University, Batac, Ilocos Norte

The reproductive potential of Eriborus argenteopilosus Cameron on Helicoverpa armigera Hubner under laboratory conditions was calculated using life table analysis. Eriborus argenteopilosus had a net reproductive rate of 36.2 and completed its generation in 21.4 days. The egg and larvae developed within 10.6 days and the pupa in 8.3 days. The intrinsic rate of increase and finite rate of increase in numbers were 0.17 and 1.18 females per female per day, respectively. With the net reproductive rate, the population of the wasp can multiply as much as 3.2 times every week.

Keywords: reproductive potential, parasitoid, Helicoverpa armigera, intrinsic rate of increase, finite rate of increase introduction during squaring to bolling stages. It attacks early instar larvae of H. armigera (Divina and Irabagon 1976; Pascua In the Philippines, many naturally occurring and Pascua 2002a) where damage is still insignificant. parasitoids can play an important role in reducing the population of the cotton bollworm, Helicoverpa armigera The reproductive potential of a parasitoid is one of (Hubner) in cotton fields (Cahatian 1990; Cacayorin et the factors to be considered in evaluating its performance al. 1993; Pascua and Pascua 1995). They can be used as biological control agent. It determines the population to manage the pest in a sustainable way. growth, and gives an idea on the efficiency of the parasitoid as a regulating agent. The reproductive potential of One of the potential parasitoid is the Eriborus both the parasitoid and the pest are essential in argenteopilosus Cameron. In a study conducted by evaluating the parasitoid’s efficiency as control agent of the Pascua and Pascua (2002a), the result shows that insect pest. One criterion of a natural enemy to become a Eriborus sp. is one of the key mortality factors of H. promising biological control agent is that its intrinsic rate of armigera and its parasitization rate ranges from 8% to 47% increase should be equal or larger than the intrinsic rate of increase of the host insect (van Lenteren 1986). *Corresponding author: [email protected]

109 Pascua LT & Pascua ME

In study conducted by Pascua and Pascua (2002a), equation and the arbitrary rm were plotted in a graph 7-r x the intrinsic rate of increase of its host, H. armigera where rm in the y axis and e m lxmx on the x axis. is 0.13 female/female/day. To assess the efficiency Other parameters were calculated using the following of E. argenteopilosus as a biological control agent, formulae: finite rate of increase in numbers(λ)= antilog rm its reproductive potential should be calculated and e ; corrected generation time (T)= log e Ro/ rm; weekly rm 7 compared with its host. multiplication of population=(e ) and hypothetical F2

females= (Ro)2.

Materials and Method Results and Discussion Second instar larvae of H. armigera were exposed in four batches to the parasitoid E. argenteopilosus in Eriborus argenteopilosus reared an H. armigera five plastic containers (approximately 8.5 cm diameter x under laboratory condition showed 20% mortality in 6 cm height) with artificial diet (Deang, 1971). For three the larval stage. Mortality was attributed to failure in days, 30 larvae per container were exposed to a mated forming cocoons (8 %) and unknown factors (12 %). parasitoid for 24 h to attain more than 25 parasitized The survivorship curve was similar to Slobodkin’s type larvae per batch or more than 100 parasitized larvae 1 (Fig. 1). The development period of egg and larval for the whole study. After exposure, the larvae were stages combined was 9 to 12 (mean=10.6 ± 0.6) days transferred to compartmentalized rearing pans and fed and the pupal stage took 7 to 9 (mean=8.3 ± 0.6) days. with artificial diet until the parasitoid larvae emerged. Males lived for 3 to 5 days, while females 1 to 9 days. One hundred parasitized larvae were randomly selected The female progeny was 57%. The actual number of five days after parasitization for the determination of eggs oviposited by the parasitoid and infertile eggs the percentage survival. Larvae of the parasitoids were were not taken into account. Gangrade (1964), found allowed to pupate and were then transferred to cages that the female Campoletis perdistinctus was not able to for emergence. distinguish between parasitized and unparasitized host larvae causing superparasitization. The occurrence of Eight pairs of newly-emerged adults were used and superparasitization in the experiment was not studied. randomly selected from each batch giving a total of 32 Mortality due to encapsulation of the eggs inside the pairs. Each pair was transferred to plastic containers insect host was not monitored. Moiseeva (1978), Norton containing 30 sec instar larvae with artificial diet every and Vinson (1977), Vinson, (1977), Moiseeva (1976) 24 h until the female parasitoid died. The parasitoids and Prevost et al. (1990) found high encapsulation rates were provided with 10 % honey solution in cotton of parasitoid eggs by different lepidopterous pests. The swabs as food. The exposed larvae were transferred to mortality of the larval parasitoid inside the host body compartmentalized rearing pans and fed with artificial was not monitored except when the host died before diet until the parasitoid larvae emerged. The parasitoids the emergence of the parasitoid. were allowed to pupate and then transferred to cages for adult emergence. The number of female progeny Five days after parasitization, the parasitized was recorded. larvae were pale, restless and hardly fed. The growth and development of the insect host was affected by An age-specific life table was constructed. the growing parasitoid inside its body. According to Survivorship (lx), expected number of daughters at age Wilson and Ridgway (1975), Campoletis sonorensis x (mx), net reproductive rate (Ro=lxmx), mean generation feeds on the hemolymph, adipose tissues and time (T=xlxmx/lxmx) and intrinsic rate of increase (r=log malphigian tubules. e Ro/T) were calculated (Southwood and Henderson Six to seven days after parasitization, the larval 2000; Price 1984). hosts ceased feeding, produced less frass and were still at the third instar while healthy larvae were already The corrected intrinsic rate of increase (rm) was calculated using the equation: at their fourth instar. Ashley (1983) made similar observation on Spodoptera frugiperda parasitized by Campoletis grioti, Apanteles marginiventus, Chelonus 7 -r x insularis and Eiphosoma vitticle. ∑e m lxmx = 1 Seven to eight days after parasitization, the parasitized host larvae buried themselves into the Two arbitrary rm values of 0.12 and 0.18 were artificial diet or dried feces and then the host insect

designated based on the ranges of calculated rm died. The movement of the host body was caused by using 32 replicates. The extracted numbers from the the presence of the parasitoid.

110 Reproductive Potential of Wasp Reared on Second Instar Cotton Bollworm (%)

Figure 1. Survival of Eriborus argenteopilosus reared in Helicoverpa armigera under laboratory condition

The parasitoid emerged as a vermiform larva from and six generations in cotton fields. Four generations the abdominal segment of the host larva leaving only can coincide with the peak population of early instars the head capsule and the thin skin of their hosts. The of H. armigera. larvae moved around for three to four hours and then started spinning, forming white cocoons which turned Its population can multiply 3.2 times every week black after six to eight hours. Some larvae moved for and hypothetically, would have 1360 females at the several hours and failed to form cocoons resulting in second filial generation (Table 2). The intrinsic rate of increase (r ) and finite rate of increase in numbers death after two days. m were 0.17 and 1.18 females/female/day, respectively. The survival of the parasitoid from the larval to pupal Upon reaching the stable age-distribution, the stage may have been higher, if an appropriate pupation population age composition of E. argenteopilosus medium was provided. The parasitoid was left in the was 87.8 % eggs and larvae, 9.9% pupa, and 2.3%, rearing pans contributing to a high percentage of the adults (Table 3). parasitoid failing to pupate. The intrinsic rate of increase is a useful parameter The female had a preoviposition period of one to determine the different factors affecting the growth day (19th day) and started to lay eggs during the 20th potential of the population and assess the potential day. Fecundity was highest at the 22nd day (mx=9.3) of E. argenteopilosus as a biological control agent of (Table 1). H. armigera. Studies in search for a suitable pupating medium should be conducted. This could decrease The parasitoid had a net reproductive rate of the failure to pupate, leading to a higher intrinsic rate 36.2 and completed a generation in 21.4 d. The net of increase. reproductive rate implies that the female population of E. argenteopilosus can increase 36 times at the The intrinsic rate of increase of E. argenteopilosus end of the next generation or 1360 at the second filial was 23 % higher than its host insect, H. armigera (Pascua generation. The generation time also indicates that this and Pascua 2002a). Therefore, E. argenteopilosus could parasitoid can complete 17 generations during a year be an effective biological control agent of H. armigera.

111 Pascua LT & Pascua ME

At low pest densities, the rm is not an efficient help the parasitoid multiply faster. Other lepidopterous measure of the parasitoid’s effectiveness because the pests that are known to be hosts of E. argenteopilosus full reproductive potential of the natural enemy may not which do not give economic damage to the crop should be realized (van Lenteren and Woets 1988). However, in be allowed to multiply in the field. However, these other actual field situation and with the overlapping generations pests should be less preferred by E. argenteopilosus, and high percentage of early instars (Pascua and otherwise, this becomes disadvantageous in controlling Pascua 2002b), E. argenteopilosus becomes efficient. of H. armigera particularly when high population of larvae The presence of other hosts in the field becomes occurs. The control may be focused on other lepidopterous advantageous to E. argenteopilosus because these could pests rather than the key pest, H. armigera.

Table 1. Life table (for females) and age-specific fecundity of Eriborus argenteopilosus reared on Helicoverpa armigera under laboratory condition at 26 to 30 °C

X lx mx lxmx xlxmx

0-18

19 0.80 * 0.80 0.80

20 0.80 6.15 4.92 98.40

21 0.77 8.63 6.65 139.55

22 0.77 9.31 7.17 157.71

23 0.65 8.61 5.60 128.72

24 0.56 7.91 4.43 106.31

25 0.47 7.14 3.36 83.90

26 0.32 6.00 1.92 49.92

27 0.26 5.00 1.30 35.1

28 0.11

36.15 800.41

Table 2. Population development parameters of Eriborus argenteopilosus reared on Helicoverpa armigera Eriborus Helicoverpa armigera Parameters argenteopilosus (Pascua and Pascua, 2002a)

Generation time (days) 21.14 41.11

Net reproductive rate 36.15 171.87

Rate of population increase (female/female/ 0.16 0.12 day) Corrected rate of population increase 0.17 0.13 (female/female/day)

Corrected generation time (days) 21.36 39.71

Finite rate of increase in numbers 1.18 1.40 (females/female/day)

Weekly multiplication of population 3.24 2.48

Hypothetical F2 females 1360.82 2939.30

112 Reproductive Potential of Wasp Reared on Second Instar Cotton Bollworm

Table 3. Stable age-distribution of Eriborus argenteopilosus reared on Helicoverpa armigera (rm=0.173)

-rm(x+1) -rm (x+1) β -rm(x+1) x Lx e Lx e % distribution 100 Lx e 0 1.00 0.845 0.845 16.446 1 1.00 0.714 0.714 13.896 2 1.00 0.604 0.604 11.756 3 1.00 0.511 0.511 9.946 Egg and larva = 87.8 4 1.00 0.432 0.432 8.408 5 1.00 0.365 0.365 7.104 6 0.92 0.309 0.284 5.527 7 0.92 0.261 0.240 4.671 8 0.92 0.220 0.203 3.951 9 0.92 0.186 0.171 3.328 10 0.92 0.158 0.145 2.822 11 0.88 0.133 0.117 2.277 12 0.83 0.096 0.078 1.518 13 0.80 0.095 0.076 1.479 14 0.80 0.080 0.064 1.245 Pupa = 9.9 15 0.80 0.068 0.054 1.051 16 0.80 0.057 0.046 0.895 17 0.80 0.049 0.039 0.759 18 0.80 0.041 0.033 0.642 19 0.80 0.035 0.028 0.545 20 0.80 0.029 0.023 0.448 21 0.77 0.025 0.019 0.370 22 0.77 0.021 0.016 0.311 Adult = 2.3 23 0.65 0.018 0.012 0.234 24 0.56 0.015 0.008 0.156 25 0.47 0.013 0.006 0.117 26 0.32 0.011 0.003 0.058 27 0.26 0.009 0.002 0.039 1/β=5.138

Acknowledgments References The authors express their heartfelt thanks to Ashley TR. 1983. Growth pattern alterations on following: the Cotton Research and Development fall army worm, Spodoptera frugiferda larvae Institute (now the Cotton Development Administration) after parasitization of Apanteles marginiventus, for funding the research; Dr. Isagani G. Catedral, Campoletis grioti, Chelonus insularis and Eiphosoma Dr. Eugenio D. Orpia, Jr and Mr. Yolando M. Madriaga vitticle. Florida Entomol 66:260-266. for their support on the conduct of the experiment; Cahatian GO. 1990. Natural enemies of Helicoverpa Mr. Elmer Santiago for helping in data computation; armigera (Hubner). [M. S. Thesis]. College, Laguna, Prof. Dr. Joop van Lenteren, Dr. Arnold van Huis, Philippines: University of the Philippines Los Dr. Epifania O. Agustin, Dr. Sosimo Ma. Pablico and Baños. Dr. Rey Velasco for their helpful comments and editing this paper and Dr. Rob Zwart for identifying Eriborus Cacayorin ND, Solsoloy AD, Damo MC & Solsoloy TS. argenteopilosus. 1993. Beneficial regulating population of insect pests of cotton. Cotton Res J (Phil.) 6:1-8.

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