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Impact of the entomopathogenic fungus Verticillium lecanii on development of an aphid parasitoid, Aphidius colemani
Journal of Invertebrate Pathology 88 (2005) 254–256 www.elsevier.com/locate/yjipa
Short communication
Impact of the entomopathogenic fungus Verticillium lecanii on development of an aphid parasitoid, Aphidius colemani Jeong Jun Kim a
a,¤
, Kyu Chin Kim b, Donald W. Roberts
c
Applied Entomology Division, NIAST, RDA, Sedundong 249, Suwon 441-707, Republic of Korea b Department of Agrobiology, Chonnam National University, Republic of Korea c Department of Biology, Utah State University, Logan, UT 84322-5305, USA Received 27 April 2004; accepted 6 January 2005 Available online 22 February 2005
Abstract The parasitoid Aphidius colemani developed normally (approximately 90% adult emergence) when its cotton aphid (Aphis gossypii) host was treated with Verticillum lecanii conidia 5 or 7 days after parasitization. Fungus exposure 1 day before or up to 3 days after parasitization, however, reduced A. colemani emergence from 0 to 10%. Also, numbers of spores and mycelial fragments in aphid homogenates were much higher in aphids exposed to the fungus up to 3 days after parasitization than in aphids treated after 5 or 7 days. Our results suggest that the parasitoid and fungus may be used together for aphid biocontrol as long as fungus applications are timed to allow late-instar development of the parasitoid. 2005 Elsevier Inc. All rights reserved. Keywords: Verticillium lecanii; Interaction; Parasitoid; Cotton aphid (Aphis gossypii); Aphidius colemani
The use of entomopathogens and natural enemies as alternative pest-control agents is rapidly increasing in greenhouses. Various entomopathogens and/or natural enemies often are introduced simultaneously or nearly simultaneously to control aphids because these insects have very high reproductive rates and are very diYcult to control using only a single biological control agent (Gullino et al., 1999). These biological-control agents may act synergistically, additively or antagonistically. Synergistic interactions between pathogens and insect natural enemies will enhance control eYcacy, whereas antagonistic interactions will reduce total control eYcacy (Roy and Pell, 2000). For example, adult females of Aphelinus asychis, a common parasitoid of Russian wheat aphid, Diuraphis noxia, exposed to Paecilomyces fumosoroseus conidia at high humidity and at high path-
¤
Corresponding author. Fax: +82 31 290 0407. E-mail addresses: [email protected], [email protected] (J.J. Kim).
0022-2011/$ - see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2005.01.004
ogen dose signiWcantly reduced host searching (walking time, speed, and distance) (Lacey et al., 1997). Accordingly, interactions between speciWc entomopathogenic fungi and natural enemies should be examined before their use in wide-scale Weld or greenhouse pest-control systems, e.g., aphid control in greenhouses. Verticillium lecanii is a well-known entomopathogenic fungus which has been commercialized for aphid and whiteXy control (Milner, 1997). Zare and Gams (2001) have proposed that Verticilllium lecanii isolates be renamed as members of the genus Lecanicillium. One isolate of V. lecanii (CS-625) from Korea has conWrmed high virulence against cotton aphid, Aphis gossypii (Kim et al., 2001). The inXuence of this strain of V. lecanii on an aphid parasitoid, Aphidius colemani, is reported here. The aphid parasitoid A. colemani was reared in an alternative aphid host, Schizaphis graminum, on barley seedlings. One-day-old cotton aphids (A. gossypii) reared on greenhouse cucumber plants were Wrst exposed in groups of 10 two-day-old A. colemani adults for 24 h.
J.J. Kim et al. / Journal of Invertebrate Pathology 88 (2005) 254–256
The groups of aphids were sprayed with 1 £ 108 V. lecanii conidia/ml, a concentration known to kill 100% of cotton aphid (Kim et al., 2001), either 1 day before or 0, 3, 5, or 7 days after parasitoid exposure. Both mummiWcation of cotton aphids and emergence of adults of A. colemani from cotton aphids were recorded. Fungal infection of A. colemani was conWrmed by stereomicroscope observation and quantiWed by colony-forming-unit (CFU) counts in insect homogenates using potato-dextrose-agar medium containing antibacterial antibiotics (100,000 IU penicillin/ 100,000 g streptomycin per liter). The mummiWcation of parasitized aphids, as well as emergence and infection of the parasitoid diVered with the application times of spore suspensions. Successful parasitism, as indicated by mummiWcation of aphids and emergence of parasitoids from mummies, was severely reduced following spore treatments 1 day before or 0 to 3 days after exposure to the parasitoid; but there was little impact when the spore treatment was at 5 or 7 days after parasitoid application (Table 1). Mycosis in treated aphids or mummies was signiWcantly aVected, depending on time of exposure to spores. Mycosis rates in parasitoids were high with the Wrst three treatment times, but not detected with the 5- and 7-day exposure dates (Table 1). Also, numbers of spores plus mycelial fragments (CFU) were higher in aphids sprayed at the Wrst three treatment times than at the Wnal two dates (Fig. 1). Timing of fungal spore applications to the hosts of parasitoids is important to the successful development of the parasitoids, with the outcome being aVected by whether the insect hosts were Wrst infected by the pathogen or if they were Wrst parasitized by the parasitoid as documented in the case of an isolate of V. lecanii infecting Aphidius nigripes, a parasitoid of potato aphid, Macrosiphum euphorbiae (Askary and Brodeur, 1999). Also, infection rates of Encarsia formosa, a greenhouse whiteXy parasitoid, by Aschersonia aleyrodis varied with timing of spore application after parasitization (Fransen and van Lenteren, 1994). The number of parasitized whiteXy Table 1 Mycosis, mummiWcation, and adult-emergence rate of the aphid parasitoid A. colemani after spraying with V. lecanii conidia at diVerent days following parasitoid exposure Fungus treatment Mycosis(%) MummiWcation (%) Adult (time of spraying with at 7th day at 7th day emergency conidia before/after (%) parasite exposure) Control (no fungus) 1 day before Immediately after 3 days after 5 days after 7 days after
0.0 c 96.6 a 88.0 ab 79.7 b 0.0 c 0.0 c
88.6 a 7.5 c 11.6 c 63.3 b 86.7 a 94.1 a
96.2 a 0.0 b 2.2 b 10.3 b 84.4 a 92.0 a
Adult emergence was recorded from days 9 to 11 following exposure to A. colemani. Means followed by the same letter in the same column are not signiWcantly diVerent at the 0.05% level as determined by the Student’s t test.
255
Fig. 1. Number of spores and mycelial fragments of V. lecanii CS-625 in A. colemani larvae homogenized 5 or 7 days after being sprayed with spores at diVerent developmental stages of the parasite. Means in the same bar followed by the same letters are not signiWcantly diVerent at the 0.05% level as determined by the Student’s t test
pupae was signiWcantly reduced by spore treatment 1–3 days after oviposition in whiteXy nymphs, whereas spore treatment at 4–10 days did not reduce parasitization (as compared with untreated controls). Also, blastospores of Paecilomyces fumosoroseus sprayed on greenhouse whiteXies (Trialeurodes vaporariorum) 4 days after exposure to the parasitoid Encarsia formosa did not inhibit parasitoid development (P.B. Avery, personal communication). Although a parasitoid may not die of direct infection of its host by a pathogen, the altered nutritional status and premature death of a fungus-infected aphid host may negatively aVect parasitoid survival (Brooks, 1993). According to Washburn et al. (2000), parasitized larvae of tobacco hornworm were more susceptible to viral infection than nonparasitized larvae because of immunosuppression by the parasitoid’s polydnavirus. Our data do not prove that parasitization stimulated fungal infection of either the host aphids or the parasitoid’s larvae. Both direct fungal infection and malformed parasitoid larvae or pupae were observed on dissection of mummies from aphids treated with spores shortly after parasitoid exposure. The cuticle of mummiWed aphids sprayed with fungal spores 5- and 7-days after parasitoid exposure were not penetrated by V. lecanii. In conclusion, our results suggest that combined use of both A. colemani and V. lecanii for integrated pest management of aphids is a viable control option; but fungal spore applications, should as much as possible be timed to coincide with the later developmental stages of the parasitoid to conserve the parasitoids within the system.
Acknowledgment We are grateful to Dr. C.S. Yoon of Korea University, Seoul, Korea, for providing the V. lecanii CS-625.
256
J.J. Kim et al. / Journal of Invertebrate Pathology 88 (2005) 254–256
References Askary, H., Brodeur, J., 1999. Susceptibility of larval stages of the aphid parasitoid Aphidius nigripes to the entomopathogenic fungus Verticillium lecanii. J. Invertebr. Pathol. 73, 129–132. Brooks, W.M., 1993. Host–parasitoid–pathogen interaction. In: Beckage, N.E., Thompson, S.N., Federici, B.A. (Eds.), Parasites and Pathogens of Insects, vol. 2. Academic Press, London, pp. 231–272. Fransen, J.J., van Lenteren, J., 1994. Survival of the parasitoid Encarsia formosa after treatment of parasitized greenhouse whiteXy larvae with fungal spores of Aschersonia aleyrodis. Entomol. Exp. Appl. 71, 235–243. Gullino, M.L., Albajes, R., van Lenteren, J.C., 1999. Characteristics of protected cultivation and tools for sustainable crop protection. In: Albajes, R., Gullino, M.L., van Lenteren, J.C., Elad, Y. (Eds.), Integrated Pest Management in Greenhouse Crops. Kluwer Academic, Boston, USA, pp. 1–15. Kim, J.J., Lee, M.H., Yoon, C.S., Kim, H.S., Yoo, J.K., Kim, K.C., 2001. Control of cotton aphid and greenhouse whiteXy with a fungal pathogen. In: “Biological control of greenhouse pests”. Food &
Fertilizer Technology Center Extension Bulletin 502, Food & Fertilizer Technology Center, Taipei, Taiwan, pp. 8–15. Lacey, L.A., Mesquita, A.L.M., Mercadier, G., Debire, R., Kazmer, D.J., Leclant, F., 1997. Acute and sublethal activity of the entomopathogenic fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) on adult Aphelinus asychis (Hymenoptera: Aphelinidae). Environ. Entomol. 26, 1452–1460. Milner, R.J., 1997. Prospects for biopesticides for aphid control. Entomophaga 42, 227–239. Roy, E.H., Pell, J.K., 2000. Interactions between entomopathogenic fungi and other natural enemies: Implications for biological control. Biocontrol Sci. Technol. 10, 737–752. Washburn, O.J., Haas-Stapleton, J.E., Tan, F.F., Beckage, E.N., Volkman, E.L., 2000. Co-infection of Manduca Sexta larvae with polydnavirus from Cotesia congregata increases susceptibility to fatal infection by Autographa californica M nucleopolyhedrovirus. J. Insect. Physiol. 46, 179–190. Zare, R., Gams, W., 2001. A revision of Verticillium section Protrata. IV. The genera Lecanicillium and Simplicillium. Nova Hedwigia 73, 1–50.
Short communication
Impact of the entomopathogenic fungus Verticillium lecanii on development of an aphid parasitoid, Aphidius colemani Jeong Jun Kim a
a,¤
, Kyu Chin Kim b, Donald W. Roberts
c
Applied Entomology Division, NIAST, RDA, Sedundong 249, Suwon 441-707, Republic of Korea b Department of Agrobiology, Chonnam National University, Republic of Korea c Department of Biology, Utah State University, Logan, UT 84322-5305, USA Received 27 April 2004; accepted 6 January 2005 Available online 22 February 2005
Abstract The parasitoid Aphidius colemani developed normally (approximately 90% adult emergence) when its cotton aphid (Aphis gossypii) host was treated with Verticillum lecanii conidia 5 or 7 days after parasitization. Fungus exposure 1 day before or up to 3 days after parasitization, however, reduced A. colemani emergence from 0 to 10%. Also, numbers of spores and mycelial fragments in aphid homogenates were much higher in aphids exposed to the fungus up to 3 days after parasitization than in aphids treated after 5 or 7 days. Our results suggest that the parasitoid and fungus may be used together for aphid biocontrol as long as fungus applications are timed to allow late-instar development of the parasitoid. 2005 Elsevier Inc. All rights reserved. Keywords: Verticillium lecanii; Interaction; Parasitoid; Cotton aphid (Aphis gossypii); Aphidius colemani
The use of entomopathogens and natural enemies as alternative pest-control agents is rapidly increasing in greenhouses. Various entomopathogens and/or natural enemies often are introduced simultaneously or nearly simultaneously to control aphids because these insects have very high reproductive rates and are very diYcult to control using only a single biological control agent (Gullino et al., 1999). These biological-control agents may act synergistically, additively or antagonistically. Synergistic interactions between pathogens and insect natural enemies will enhance control eYcacy, whereas antagonistic interactions will reduce total control eYcacy (Roy and Pell, 2000). For example, adult females of Aphelinus asychis, a common parasitoid of Russian wheat aphid, Diuraphis noxia, exposed to Paecilomyces fumosoroseus conidia at high humidity and at high path-
¤
Corresponding author. Fax: +82 31 290 0407. E-mail addresses: [email protected], [email protected] (J.J. Kim).
0022-2011/$ - see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2005.01.004
ogen dose signiWcantly reduced host searching (walking time, speed, and distance) (Lacey et al., 1997). Accordingly, interactions between speciWc entomopathogenic fungi and natural enemies should be examined before their use in wide-scale Weld or greenhouse pest-control systems, e.g., aphid control in greenhouses. Verticillium lecanii is a well-known entomopathogenic fungus which has been commercialized for aphid and whiteXy control (Milner, 1997). Zare and Gams (2001) have proposed that Verticilllium lecanii isolates be renamed as members of the genus Lecanicillium. One isolate of V. lecanii (CS-625) from Korea has conWrmed high virulence against cotton aphid, Aphis gossypii (Kim et al., 2001). The inXuence of this strain of V. lecanii on an aphid parasitoid, Aphidius colemani, is reported here. The aphid parasitoid A. colemani was reared in an alternative aphid host, Schizaphis graminum, on barley seedlings. One-day-old cotton aphids (A. gossypii) reared on greenhouse cucumber plants were Wrst exposed in groups of 10 two-day-old A. colemani adults for 24 h.
J.J. Kim et al. / Journal of Invertebrate Pathology 88 (2005) 254–256
The groups of aphids were sprayed with 1 £ 108 V. lecanii conidia/ml, a concentration known to kill 100% of cotton aphid (Kim et al., 2001), either 1 day before or 0, 3, 5, or 7 days after parasitoid exposure. Both mummiWcation of cotton aphids and emergence of adults of A. colemani from cotton aphids were recorded. Fungal infection of A. colemani was conWrmed by stereomicroscope observation and quantiWed by colony-forming-unit (CFU) counts in insect homogenates using potato-dextrose-agar medium containing antibacterial antibiotics (100,000 IU penicillin/ 100,000 g streptomycin per liter). The mummiWcation of parasitized aphids, as well as emergence and infection of the parasitoid diVered with the application times of spore suspensions. Successful parasitism, as indicated by mummiWcation of aphids and emergence of parasitoids from mummies, was severely reduced following spore treatments 1 day before or 0 to 3 days after exposure to the parasitoid; but there was little impact when the spore treatment was at 5 or 7 days after parasitoid application (Table 1). Mycosis in treated aphids or mummies was signiWcantly aVected, depending on time of exposure to spores. Mycosis rates in parasitoids were high with the Wrst three treatment times, but not detected with the 5- and 7-day exposure dates (Table 1). Also, numbers of spores plus mycelial fragments (CFU) were higher in aphids sprayed at the Wrst three treatment times than at the Wnal two dates (Fig. 1). Timing of fungal spore applications to the hosts of parasitoids is important to the successful development of the parasitoids, with the outcome being aVected by whether the insect hosts were Wrst infected by the pathogen or if they were Wrst parasitized by the parasitoid as documented in the case of an isolate of V. lecanii infecting Aphidius nigripes, a parasitoid of potato aphid, Macrosiphum euphorbiae (Askary and Brodeur, 1999). Also, infection rates of Encarsia formosa, a greenhouse whiteXy parasitoid, by Aschersonia aleyrodis varied with timing of spore application after parasitization (Fransen and van Lenteren, 1994). The number of parasitized whiteXy Table 1 Mycosis, mummiWcation, and adult-emergence rate of the aphid parasitoid A. colemani after spraying with V. lecanii conidia at diVerent days following parasitoid exposure Fungus treatment Mycosis(%) MummiWcation (%) Adult (time of spraying with at 7th day at 7th day emergency conidia before/after (%) parasite exposure) Control (no fungus) 1 day before Immediately after 3 days after 5 days after 7 days after
0.0 c 96.6 a 88.0 ab 79.7 b 0.0 c 0.0 c
88.6 a 7.5 c 11.6 c 63.3 b 86.7 a 94.1 a
96.2 a 0.0 b 2.2 b 10.3 b 84.4 a 92.0 a
Adult emergence was recorded from days 9 to 11 following exposure to A. colemani. Means followed by the same letter in the same column are not signiWcantly diVerent at the 0.05% level as determined by the Student’s t test.
255
Fig. 1. Number of spores and mycelial fragments of V. lecanii CS-625 in A. colemani larvae homogenized 5 or 7 days after being sprayed with spores at diVerent developmental stages of the parasite. Means in the same bar followed by the same letters are not signiWcantly diVerent at the 0.05% level as determined by the Student’s t test
pupae was signiWcantly reduced by spore treatment 1–3 days after oviposition in whiteXy nymphs, whereas spore treatment at 4–10 days did not reduce parasitization (as compared with untreated controls). Also, blastospores of Paecilomyces fumosoroseus sprayed on greenhouse whiteXies (Trialeurodes vaporariorum) 4 days after exposure to the parasitoid Encarsia formosa did not inhibit parasitoid development (P.B. Avery, personal communication). Although a parasitoid may not die of direct infection of its host by a pathogen, the altered nutritional status and premature death of a fungus-infected aphid host may negatively aVect parasitoid survival (Brooks, 1993). According to Washburn et al. (2000), parasitized larvae of tobacco hornworm were more susceptible to viral infection than nonparasitized larvae because of immunosuppression by the parasitoid’s polydnavirus. Our data do not prove that parasitization stimulated fungal infection of either the host aphids or the parasitoid’s larvae. Both direct fungal infection and malformed parasitoid larvae or pupae were observed on dissection of mummies from aphids treated with spores shortly after parasitoid exposure. The cuticle of mummiWed aphids sprayed with fungal spores 5- and 7-days after parasitoid exposure were not penetrated by V. lecanii. In conclusion, our results suggest that combined use of both A. colemani and V. lecanii for integrated pest management of aphids is a viable control option; but fungal spore applications, should as much as possible be timed to coincide with the later developmental stages of the parasitoid to conserve the parasitoids within the system.
Acknowledgment We are grateful to Dr. C.S. Yoon of Korea University, Seoul, Korea, for providing the V. lecanii CS-625.
256
J.J. Kim et al. / Journal of Invertebrate Pathology 88 (2005) 254–256
References Askary, H., Brodeur, J., 1999. Susceptibility of larval stages of the aphid parasitoid Aphidius nigripes to the entomopathogenic fungus Verticillium lecanii. J. Invertebr. Pathol. 73, 129–132. Brooks, W.M., 1993. Host–parasitoid–pathogen interaction. In: Beckage, N.E., Thompson, S.N., Federici, B.A. (Eds.), Parasites and Pathogens of Insects, vol. 2. Academic Press, London, pp. 231–272. Fransen, J.J., van Lenteren, J., 1994. Survival of the parasitoid Encarsia formosa after treatment of parasitized greenhouse whiteXy larvae with fungal spores of Aschersonia aleyrodis. Entomol. Exp. Appl. 71, 235–243. Gullino, M.L., Albajes, R., van Lenteren, J.C., 1999. Characteristics of protected cultivation and tools for sustainable crop protection. In: Albajes, R., Gullino, M.L., van Lenteren, J.C., Elad, Y. (Eds.), Integrated Pest Management in Greenhouse Crops. Kluwer Academic, Boston, USA, pp. 1–15. Kim, J.J., Lee, M.H., Yoon, C.S., Kim, H.S., Yoo, J.K., Kim, K.C., 2001. Control of cotton aphid and greenhouse whiteXy with a fungal pathogen. In: “Biological control of greenhouse pests”. Food &
Fertilizer Technology Center Extension Bulletin 502, Food & Fertilizer Technology Center, Taipei, Taiwan, pp. 8–15. Lacey, L.A., Mesquita, A.L.M., Mercadier, G., Debire, R., Kazmer, D.J., Leclant, F., 1997. Acute and sublethal activity of the entomopathogenic fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) on adult Aphelinus asychis (Hymenoptera: Aphelinidae). Environ. Entomol. 26, 1452–1460. Milner, R.J., 1997. Prospects for biopesticides for aphid control. Entomophaga 42, 227–239. Roy, E.H., Pell, J.K., 2000. Interactions between entomopathogenic fungi and other natural enemies: Implications for biological control. Biocontrol Sci. Technol. 10, 737–752. Washburn, O.J., Haas-Stapleton, J.E., Tan, F.F., Beckage, E.N., Volkman, E.L., 2000. Co-infection of Manduca Sexta larvae with polydnavirus from Cotesia congregata increases susceptibility to fatal infection by Autographa californica M nucleopolyhedrovirus. J. Insect. Physiol. 46, 179–190. Zare, R., Gams, W., 2001. A revision of Verticillium section Protrata. IV. The genera Lecanicillium and Simplicillium. Nova Hedwigia 73, 1–50.