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Potential of Steinernema carpocapsae (Weiser) as a biological control agent against potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)
Journal of Integrative Agriculture 2020, 19(2): 389–393 Available online at www.sciencedirect.com
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Potential of Steinernema carpocapsae (Weiser) as a biological control agent against potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) YAN Jun-jie1, 2, Shovon Chandra Sarkar1, MENG Rui-xia2, Stuart Reitz3, GAO Yu-lin1 1
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, P.R.China 2 College of Agronomy, Inner Mongolia Agricultural University, Hohhot 010019, P.R.China 3 Department of Crop and Soil Sciences, Malheur County Extension, Oregon State University, Ontario, OR 97914, USA
Abstract The entomopathogenic nematode, Steinernema carpocapsae, was evaluated for control of the potato tuber moth, Phthorimaea operculella, under laboratory conditions. We evaluated different concentrations of S. carpocapsae for control of 2nd, 3rd, and 4th instar P. operculella. The median lethal concentration (LC50) of S. carpocapsae infective juveniles (IJs) to 2nd, 3rd and 4th instar larvae of P. operculella was 200, 363, 181 IJs mL–1, respectively. With the extension of treatment time, the cumulative mortality increased for 2nd, 3rd, and 4th instar larvae and pupae of P. operculella. Fourth instars were the most susceptible for all observation periods. Therefore, our results suggest that S. carpocapsae could be an effective biological control agent for P. operculella. Keywords: Steinernema carpocapsae, Phthorimaea operculella, patato, integrated biological pest control
1. Introduction The potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a notorious pest of solanaceous crops, especially for potato, tobacco and eggplant, resulting in significant economic losses worldwide (Gao 2018a, b; Xu
Received 25 April, 2019 Accepted 11 September, 2019 YAN Jun-jie, Tel: +86-10-62815930, E-mail: yanjunjie125@ qq.com; Correspondence GAO Yu-lin, Tel: +86-10-62815930, E-mail: gaoyulin@ caas.cn © 2020 CAAS. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). doi: 10.1016/S2095-3119(19)62826-1
et al. 2019). It is a particularly devastating pest of potato. Larvae mainly infest leaves and petioles in the potato growth phase; while, late in the season, larvae can infest tubers in the ground and the P. operculella damages tubers seriously during storage (Rondon 2010). Until the last two decades, control of P. operculella has relied upon the use of the traditional insecticides (Szendrei 1986; Kroschel 1995); however, insecticide-based control has become difficult due to the rapid development of resistance to insecticides (Doğramaci and Tingey 2010; Hafez 2011). Recently, biological control of P. operculella has become important in both field production and potato storage (Kepenekci et al. 2013). Entomopathogenic nematodes can effectively control a variety of soil-borne pests (Shapiro and Mccoy 2000; Yadav 2012). Steinernema carpocapsae (Weiser) (Nematoda: Steinernematidae) also is particularly effective against lepidopteran larvae, as well as species
390
YAN Jun-jie et al. Journal of Integrative Agriculture 2020, 19(2): 389–393
that mine within leaves or other protected habitats (Wilson et al. 2012; Kepenekci et al. 2013). This study was to investigate the effectiveness of S. carpocapsae against P. operculella under laboratory conditions to provide a basis for development of biological control techniques.
2. Materials and methods A total of about 500 Phthorimaea operculella adults were collected from a potato field in Kunming, Yunnan Province, China (103°79´E, 25°5´N) in 2014. Phthorimaea operculella were maintained in culture as described by Rondon et al. (2009). Briefly, the colony was maintained at (27±2)°C, 60% RH and photoperiod of 12 h L:12 h D. Larvae were reared in plastic containers. As a food source, a potato tuber with a diameter of about 6 cm was placed in each container, and fine sand was placed in the bottom of the container for pupation. Age is distinguished by the life table of P. operculella at 26°C (Jin et al. 2005). Pupae were transferred to cylindrical containers for adult eclosion. Cylinders had a diameter of 14 cm and a height of 10 cm. The top of the cylinders were covered with gauze cloth and filter paper (9 cm in diameter) and placed over the gauze as an oviposition substrate. A 5% honey water solution was streaked on the gauze as a food source for adults. Steinernema carpocapsae were provided by Zhejiang Green God Natural Enemy Biotechnology Co., Ltd., China and stored in water-soaked sponges held at (10±1)°C. The storage period was not more than 15 days. The nematode was reared in vivo on late instar Tenebrio molitor L. according to the methods of White (1927). Infective juveniles (IJs) of S. carpocapsae were collected from cultures at days 12 and 15 of a generation. The storage period of filtered nematodes was used for infesting P. operculella. All laboratory experiments were conducted in Petri dishes (3.5 cm in diameter) held in an incubator at (27±2)°C, 60% RH and a photoperiod of 12 h L:12 h D. Ten individuals of the same stage were placed in a Petri dish to comprise an experimental replicate. There were three replicates for each treatment in this experiment. To screen mortality effects of S. carpocapsae on P. operculella, 2nd, 3rd and 4th instar larvae were treated with one of seven concentrations of S. carpocapsae IJs (100, 125, 250, 500, 625, 1 250 and 2 500 IJs mL–1, respectively). An untreated control of sterile water was also included in the trial. Ten larvae were placed on a 5-mm thick potato tuber disk, and 0.5 mL of the different concentration of S. carpocapsae suspension was evenly dropped into the corresponding Petri dish. The potato tuber disk provided nutrition for P. operculella, and also maintained high humidity in the Petri dish. Insect inactivity after external stimulation was used as
an indicator of mortality at 48 h after treatment. At this time, P. operculella was dissected and the infection of S. carpocapsae was observed, and photographs were used for evidence. This information established whether the death of P. operculella was due to infestation of S. carpocapsae. In the second experiment, P. operculella was exposed to S. carpocapsae to evaluate the mortality at 24, 48, 72 and 96 h after the treatment of 200 IJs mL–1 on 2nd, 3rd and 4th instars of larvae and pupae. Larvae were held as described above. Pupae were placed in sand at 16% relative humidity. The status of individuals was examined every 24 h after treatment for 4 days. Mortality data were corrected for control mortality (Abbott 1925). Data were normalized using arcsine square-root transformation before being subjected to analysis of variance (ANOVA). Means were separated by the Tukey’s mean separation test at α=0.05 to determine significant differences among treatments. The median lethal concentrations (LC50) were determined by Probit regression. All analyses were conducted using the SPSS 19.0 Software.
3. Results Steinernema carpocapsae was lethal to the different stages of P. operculella larvae. There were significant differences in LC 50 among the different stages of P. operculella (F=65.01; df=2, 6; P<0.0001). Fourth and 2nd instars were the most sensitive (LC50=181 IJs mL–1; LC50=200 IJs mL–1, respectively); 3rd instar larvae were the least sensitive (LC50=363 IJs mL–1) (Table 1). There were significant differences in mortality over time (F=49.312; df=3; P=0.001) and between life stages (F=19.145; df=3; P=0.001) level. Fig. 1 shows that the mortality of P. operculella increased with the time after treatment. For example, mortality of 4th instar P. operculella at 24, 48, 72 and 96 h was 6.67, 44.44, 92.58 and 98.89%, respectively. Third and 4th instars had similar mortality rates over the 4 days of the experiment. Second instars were less susceptible to S. carpocapsae than 3rd and 4th instars. Pupae were the least susceptible to S. carpocapsae (Fig. 1). Dissection of putatively infected P. operculella revealed that S. carpocapsae can infect and reproduce in vivo in P. operculella (Fig. 2).
4. Discussion In Southwest China, P. operculella routinely infests 20 to 30% of tubers in the field and up to 100% infestation in storage (Du et al. 2006). The study which combine climatic phenology model for P. operculella with global climate change clearly indicates that the invasiveness of this pest will continue to the north from south as climatic temperatures continue to
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YAN Jun-jie et al. Journal of Integrative Agriculture 2020, 19(2): 389–393
Table 1 Median lethal concentrations (LC50) of Steinernema carpocapsae against different stages of Phthorimaea operculella larvae Life stage 2nd instar 3rd instar 4th instar 1)
LC50 (IJs mL–1)1) 200 a 363 b 181 a
95% confidence interval 112–540 225–577 137–347
Chi-square value 6.44 4.31 2.61
Regression equation Correlation coefficient y=1.00x–1.80 0.78 y=1.78x–4.07 0.90 y=1.17x–2.13 0.88
IJs, infective juveniles. LC50 values with different letters are significantly different at 0.05 level.
3rd instar
2nd instar
Pupa
4th instar c
100
b
c
c
Cumulative mortality (%)
c 80 60 b 40 b 20 0
c
c
c c
a
b
a
a
a
24
48
72
96
Time post treatment (h)
Fig. 1 Cumulative mortality for different instars of Phthorimaea operculella (2nd, 3rd, 4th instars and pupae) following exposure to Steinernema carpocapsae (200 infective juveniles mL–1). Mortality (±SE) of P. operculella larvae and pupae were treated by S. carpocapsae in the laboratory. Means with different letters are significantly different (P<0.05).
A
B
10×
C
40×
40×
Fig. 2 Steinernema carpocapsae invading the larvae of Phthorimaea operculella and multiplying within the hosts’ bodies after treatment. The red arrows refer to Steinernema carpocapsae which infected into P. operculella larvae, while the blue arrow refers to S. carpocapsae that propagated in P. operculella larvae.
rise (Kroschel et al. 2013). The increase of P. operculella
stage of P. operculella. Mortality of P. operculella increased
will severely threaten the development of the potato industry.
with time following treatment. Our results also demonstrated
Numerous studies have been conducted on the efficacy of
that S. carpocapsae casued higher mortality than observed
entomopathogenic nematodes against P. operculella larvae
in laboratory trials for other heterorhabditid nematodes
and pupae. Most of these studies have indicated that the
(Yoshida 2010; Vashisth et al. 2018) .
larvae are susceptible for nematode infection, whereas
The results of this research are especially encouraging
pupae not (Ivanova et al. 1994; Hassanikakhki et al. 2013;
as the laboratory bioassay has indicated high infectivity
Kamali et al. 2013; Kepenekci̇ et al. 2013; Kary et al. 2018).
against the larval stages of P. operculella. Applications
Our results indicate that S. carpocapsae is highly virulent to
of S. carpocapsae could be particularly promising in
P. operculella larvae and it significantly reduces the survival
targeting the 4th instars, which is the stage at which larvae
of P. operculella larvae. Steinernema carpocapsae causes
prepare to pupate at or near the soil surface in the field.
higher larval mortality and 4th instar is the most susceptible
Therefore, further research needs to be conducted in
392
YAN Jun-jie et al. Journal of Integrative Agriculture 2020, 19(2): 389–393
field conditions to support our laboratory results regarding the virulence of S. carpocapsae. In addition, given that P. operculella causes major damages in a suitable climates. Steinernema carpocapsae requires a minimum of 6% soil moisture, but survival rate of these nematodes drops significantly at higher soil moistures (Koppenhöfer et al. 1995; Yadav 2012). Therefore, more attention should be paid to the limitations of S. carpocapsae in pluvial regions, which are regions where P. operculella is a greater problem. Steinernema carpocapsae shows strong virulence to P. operculella larvae, and can be reproduced in vivo in P. operculella in the laboratory conditions. After successful infection, it may be expected to form reproducing, persistant populations to provide long-term management of P. operculella in the field.
5. Conclusion Our study indicates that S. carpocapsae may be recommended for effective biological control of P. operculella and further research needs to be done in open field experiments to support our laboratory studies regarding the efficacy of S. carpocapsae.
Acknowledgements This work was supported in part by the National Key Research and Development Program of China (2018YFD0200802).
References Abbott W S. 1925. A method for computing the effectiveness of insecticides. Journal of Economic Entomology, 18, 265–267. Doğramaci M, Tingey W M. 2010. Performance of a North American field population and a laboratory colony of the potato tuberworm, Phthorimaea operculella, on foliage of resistant and susceptible potato clones. Journal of Insect Science, 10, 80. Du L T, Li Z Y, Zhou L M. 2006. Comparative test on the control effects of three kinds of pesticides on potato tuberworm Phthorimaea opercuella (Zeller). Chinese Potato Journal, 20, 92–93. (in Chinese) Gao Y. 2018a. Potato tuberworm: A threat for China potatoes. Entomology, Ornithology & Herpetology (Current Research), 7, 2. Gao Y. 2018b. Potato tuberworm: Impact and methods for control - Mini Review. CAB Reviews, 13, 1–3. Hafez E. 2011. Insecticide resistance in potato tuber moth Phthorimaea operculella Zeller in Egypt. Journal of American Science, 7, 263–266. Hassanikakhki M, Karimi J, Hosseini M. 2013. Efficacy of entomopathogenic nematodes against potato tuber moth,
Phthorimaea operculella (Lepidoptera: Gelechiidae) under laboratory conditions. Biocontrol Science and Technology, 23, 146–159. Ivanova T S, Borovaya V P, Danilov L G. 1994. A biological method of controlling the potato moth. Zashchita Rastenii Moskva, 2, 39. (in Russian) Jin X P, Li Z Y, Chen B, Sun Y X. 2005. Experimental population life tables of potato tuber moth at different temperatures. Southwest China Journal of Agricultural Sciences, 18, 773–776. (in Chinese) Kamali S, Karimi J, Hosseini M, Campos-Herrera R, Duncan L W. 2013. Biocontrol potential of the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae on cucurbit fly, Dacus ciliatus (Diptera: Tephritidae). Biocontrol Science and Technology, 23, 1307–1323. Kary N E, Sanatipour Z, Mohammadi D, Koppenhöfer A M. 2018. Developmental stage affects the interaction of Steinernema carpocapsae and abamectin for the control of Phthorimaea operculella (Lepidoptera, Gelechidae). Biological Control, 122, 18–23. Kepenekci I, Tülek A, Alkan M, Hazır S. 2013. Biological control potential of native entomopathogenic nematodes against the potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) in Turkey. Pakistan Journal of Zoology, 45, 1415–1422. Koppenhöfer A M, Kaya H K, Taormino S P. 1995. Infectivity of entomopathogenic nematodes (Rhabditida: Steinernematidae) at different soil depths and moistures. Journal of Invertebrate Pathology, 65, 193–199. Kroschel J. 1995. Integrated pest management of potato tuber moth in the Republic of Yemen with special reference to the integrated biological control of the potato tuber moth (Phthorimaea operculella Zeller). Ph D thesis, Margraf Verlag, Weikersheim, Germany. Kroschel J, Sporleder M, Tonnang H E Z, Juarez H, Carhuapoma P, Gonzales J C, Simon R. 2013. Predicting climate-changecaused changes in global temperature on potato tuber moth Phthorimaea operculella (Zeller) distribution and abundance using phenology modeling and GIS mapping. Agricultural & Forest Meteorology, 170, 228–241. Rondon S I. 2010. The potato tuberworm: A literature review of its biology, ecology, and control. American Journal of Potato Research, 87, 149–166. Rondon S I, Hane D C, Brown C R, Vales M I, Dogramaci M. 2009. Resistance of potato germplasm to the potato tuberworm (Lepidoptera: Gelechiidae). Journal of Economic Entomology, 102, 1649–1653. Shapiro D I, McCoy C W. 2000, Virulence of entomopathogenic nematodes to Diaprepes abbreviatus (Coleoptera: Curculionidae) in the laboratory. Journal of Economic Entomology, 93, 1090–1095. Szendrei Z. 1986. Integrated pest management for potatoes in the western United States. Journal of Economic Entomology, 66, 1784–1796. Vashisth S, Chandel Y S, Chandel R S. 2018. Biological control
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potential of North West Himalayan strains of Heterorhabditid nematodes against the turnip moth, Agrotis segetum (Denis & Schiffermuller) (Lepidoptera: Noctuidae). Egyptian Journal of Biological Pest Control, 28, 37. White G F. 1927. A Method for obtaining infective nematode larvae from cultures. Science, 66, 302–303. Wilson M J, Ehlers R U, Glazer I. 2012. Entomopathogenic nematode foraging strategies - Is Steinernema carpocapsae really an ambush forager? Nematology, 14, 389–394. Xu J, Zhu J H, Yang Y L, Tang H, Lü H P, Fan M S, Shi Y, Dong D F, Wang G J, Wang W X, Xiong X Y, Gao Y L.
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Executive Editor-in-Chief WAN Fang-hao Managing editor SUN Lu-juan
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Potential of Steinernema carpocapsae (Weiser) as a biological control agent against potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) YAN Jun-jie1, 2, Shovon Chandra Sarkar1, MENG Rui-xia2, Stuart Reitz3, GAO Yu-lin1 1
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, P.R.China 2 College of Agronomy, Inner Mongolia Agricultural University, Hohhot 010019, P.R.China 3 Department of Crop and Soil Sciences, Malheur County Extension, Oregon State University, Ontario, OR 97914, USA
Abstract The entomopathogenic nematode, Steinernema carpocapsae, was evaluated for control of the potato tuber moth, Phthorimaea operculella, under laboratory conditions. We evaluated different concentrations of S. carpocapsae for control of 2nd, 3rd, and 4th instar P. operculella. The median lethal concentration (LC50) of S. carpocapsae infective juveniles (IJs) to 2nd, 3rd and 4th instar larvae of P. operculella was 200, 363, 181 IJs mL–1, respectively. With the extension of treatment time, the cumulative mortality increased for 2nd, 3rd, and 4th instar larvae and pupae of P. operculella. Fourth instars were the most susceptible for all observation periods. Therefore, our results suggest that S. carpocapsae could be an effective biological control agent for P. operculella. Keywords: Steinernema carpocapsae, Phthorimaea operculella, patato, integrated biological pest control
1. Introduction The potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a notorious pest of solanaceous crops, especially for potato, tobacco and eggplant, resulting in significant economic losses worldwide (Gao 2018a, b; Xu
Received 25 April, 2019 Accepted 11 September, 2019 YAN Jun-jie, Tel: +86-10-62815930, E-mail: yanjunjie125@ qq.com; Correspondence GAO Yu-lin, Tel: +86-10-62815930, E-mail: gaoyulin@ caas.cn © 2020 CAAS. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). doi: 10.1016/S2095-3119(19)62826-1
et al. 2019). It is a particularly devastating pest of potato. Larvae mainly infest leaves and petioles in the potato growth phase; while, late in the season, larvae can infest tubers in the ground and the P. operculella damages tubers seriously during storage (Rondon 2010). Until the last two decades, control of P. operculella has relied upon the use of the traditional insecticides (Szendrei 1986; Kroschel 1995); however, insecticide-based control has become difficult due to the rapid development of resistance to insecticides (Doğramaci and Tingey 2010; Hafez 2011). Recently, biological control of P. operculella has become important in both field production and potato storage (Kepenekci et al. 2013). Entomopathogenic nematodes can effectively control a variety of soil-borne pests (Shapiro and Mccoy 2000; Yadav 2012). Steinernema carpocapsae (Weiser) (Nematoda: Steinernematidae) also is particularly effective against lepidopteran larvae, as well as species
390
YAN Jun-jie et al. Journal of Integrative Agriculture 2020, 19(2): 389–393
that mine within leaves or other protected habitats (Wilson et al. 2012; Kepenekci et al. 2013). This study was to investigate the effectiveness of S. carpocapsae against P. operculella under laboratory conditions to provide a basis for development of biological control techniques.
2. Materials and methods A total of about 500 Phthorimaea operculella adults were collected from a potato field in Kunming, Yunnan Province, China (103°79´E, 25°5´N) in 2014. Phthorimaea operculella were maintained in culture as described by Rondon et al. (2009). Briefly, the colony was maintained at (27±2)°C, 60% RH and photoperiod of 12 h L:12 h D. Larvae were reared in plastic containers. As a food source, a potato tuber with a diameter of about 6 cm was placed in each container, and fine sand was placed in the bottom of the container for pupation. Age is distinguished by the life table of P. operculella at 26°C (Jin et al. 2005). Pupae were transferred to cylindrical containers for adult eclosion. Cylinders had a diameter of 14 cm and a height of 10 cm. The top of the cylinders were covered with gauze cloth and filter paper (9 cm in diameter) and placed over the gauze as an oviposition substrate. A 5% honey water solution was streaked on the gauze as a food source for adults. Steinernema carpocapsae were provided by Zhejiang Green God Natural Enemy Biotechnology Co., Ltd., China and stored in water-soaked sponges held at (10±1)°C. The storage period was not more than 15 days. The nematode was reared in vivo on late instar Tenebrio molitor L. according to the methods of White (1927). Infective juveniles (IJs) of S. carpocapsae were collected from cultures at days 12 and 15 of a generation. The storage period of filtered nematodes was used for infesting P. operculella. All laboratory experiments were conducted in Petri dishes (3.5 cm in diameter) held in an incubator at (27±2)°C, 60% RH and a photoperiod of 12 h L:12 h D. Ten individuals of the same stage were placed in a Petri dish to comprise an experimental replicate. There were three replicates for each treatment in this experiment. To screen mortality effects of S. carpocapsae on P. operculella, 2nd, 3rd and 4th instar larvae were treated with one of seven concentrations of S. carpocapsae IJs (100, 125, 250, 500, 625, 1 250 and 2 500 IJs mL–1, respectively). An untreated control of sterile water was also included in the trial. Ten larvae were placed on a 5-mm thick potato tuber disk, and 0.5 mL of the different concentration of S. carpocapsae suspension was evenly dropped into the corresponding Petri dish. The potato tuber disk provided nutrition for P. operculella, and also maintained high humidity in the Petri dish. Insect inactivity after external stimulation was used as
an indicator of mortality at 48 h after treatment. At this time, P. operculella was dissected and the infection of S. carpocapsae was observed, and photographs were used for evidence. This information established whether the death of P. operculella was due to infestation of S. carpocapsae. In the second experiment, P. operculella was exposed to S. carpocapsae to evaluate the mortality at 24, 48, 72 and 96 h after the treatment of 200 IJs mL–1 on 2nd, 3rd and 4th instars of larvae and pupae. Larvae were held as described above. Pupae were placed in sand at 16% relative humidity. The status of individuals was examined every 24 h after treatment for 4 days. Mortality data were corrected for control mortality (Abbott 1925). Data were normalized using arcsine square-root transformation before being subjected to analysis of variance (ANOVA). Means were separated by the Tukey’s mean separation test at α=0.05 to determine significant differences among treatments. The median lethal concentrations (LC50) were determined by Probit regression. All analyses were conducted using the SPSS 19.0 Software.
3. Results Steinernema carpocapsae was lethal to the different stages of P. operculella larvae. There were significant differences in LC 50 among the different stages of P. operculella (F=65.01; df=2, 6; P<0.0001). Fourth and 2nd instars were the most sensitive (LC50=181 IJs mL–1; LC50=200 IJs mL–1, respectively); 3rd instar larvae were the least sensitive (LC50=363 IJs mL–1) (Table 1). There were significant differences in mortality over time (F=49.312; df=3; P=0.001) and between life stages (F=19.145; df=3; P=0.001) level. Fig. 1 shows that the mortality of P. operculella increased with the time after treatment. For example, mortality of 4th instar P. operculella at 24, 48, 72 and 96 h was 6.67, 44.44, 92.58 and 98.89%, respectively. Third and 4th instars had similar mortality rates over the 4 days of the experiment. Second instars were less susceptible to S. carpocapsae than 3rd and 4th instars. Pupae were the least susceptible to S. carpocapsae (Fig. 1). Dissection of putatively infected P. operculella revealed that S. carpocapsae can infect and reproduce in vivo in P. operculella (Fig. 2).
4. Discussion In Southwest China, P. operculella routinely infests 20 to 30% of tubers in the field and up to 100% infestation in storage (Du et al. 2006). The study which combine climatic phenology model for P. operculella with global climate change clearly indicates that the invasiveness of this pest will continue to the north from south as climatic temperatures continue to
391
YAN Jun-jie et al. Journal of Integrative Agriculture 2020, 19(2): 389–393
Table 1 Median lethal concentrations (LC50) of Steinernema carpocapsae against different stages of Phthorimaea operculella larvae Life stage 2nd instar 3rd instar 4th instar 1)
LC50 (IJs mL–1)1) 200 a 363 b 181 a
95% confidence interval 112–540 225–577 137–347
Chi-square value 6.44 4.31 2.61
Regression equation Correlation coefficient y=1.00x–1.80 0.78 y=1.78x–4.07 0.90 y=1.17x–2.13 0.88
IJs, infective juveniles. LC50 values with different letters are significantly different at 0.05 level.
3rd instar
2nd instar
Pupa
4th instar c
100
b
c
c
Cumulative mortality (%)
c 80 60 b 40 b 20 0
c
c
c c
a
b
a
a
a
24
48
72
96
Time post treatment (h)
Fig. 1 Cumulative mortality for different instars of Phthorimaea operculella (2nd, 3rd, 4th instars and pupae) following exposure to Steinernema carpocapsae (200 infective juveniles mL–1). Mortality (±SE) of P. operculella larvae and pupae were treated by S. carpocapsae in the laboratory. Means with different letters are significantly different (P<0.05).
A
B
10×
C
40×
40×
Fig. 2 Steinernema carpocapsae invading the larvae of Phthorimaea operculella and multiplying within the hosts’ bodies after treatment. The red arrows refer to Steinernema carpocapsae which infected into P. operculella larvae, while the blue arrow refers to S. carpocapsae that propagated in P. operculella larvae.
rise (Kroschel et al. 2013). The increase of P. operculella
stage of P. operculella. Mortality of P. operculella increased
will severely threaten the development of the potato industry.
with time following treatment. Our results also demonstrated
Numerous studies have been conducted on the efficacy of
that S. carpocapsae casued higher mortality than observed
entomopathogenic nematodes against P. operculella larvae
in laboratory trials for other heterorhabditid nematodes
and pupae. Most of these studies have indicated that the
(Yoshida 2010; Vashisth et al. 2018) .
larvae are susceptible for nematode infection, whereas
The results of this research are especially encouraging
pupae not (Ivanova et al. 1994; Hassanikakhki et al. 2013;
as the laboratory bioassay has indicated high infectivity
Kamali et al. 2013; Kepenekci̇ et al. 2013; Kary et al. 2018).
against the larval stages of P. operculella. Applications
Our results indicate that S. carpocapsae is highly virulent to
of S. carpocapsae could be particularly promising in
P. operculella larvae and it significantly reduces the survival
targeting the 4th instars, which is the stage at which larvae
of P. operculella larvae. Steinernema carpocapsae causes
prepare to pupate at or near the soil surface in the field.
higher larval mortality and 4th instar is the most susceptible
Therefore, further research needs to be conducted in
392
YAN Jun-jie et al. Journal of Integrative Agriculture 2020, 19(2): 389–393
field conditions to support our laboratory results regarding the virulence of S. carpocapsae. In addition, given that P. operculella causes major damages in a suitable climates. Steinernema carpocapsae requires a minimum of 6% soil moisture, but survival rate of these nematodes drops significantly at higher soil moistures (Koppenhöfer et al. 1995; Yadav 2012). Therefore, more attention should be paid to the limitations of S. carpocapsae in pluvial regions, which are regions where P. operculella is a greater problem. Steinernema carpocapsae shows strong virulence to P. operculella larvae, and can be reproduced in vivo in P. operculella in the laboratory conditions. After successful infection, it may be expected to form reproducing, persistant populations to provide long-term management of P. operculella in the field.
5. Conclusion Our study indicates that S. carpocapsae may be recommended for effective biological control of P. operculella and further research needs to be done in open field experiments to support our laboratory studies regarding the efficacy of S. carpocapsae.
Acknowledgements This work was supported in part by the National Key Research and Development Program of China (2018YFD0200802).
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