Bacillus thuringiensis

Kill black cutworms (Agrotis ipsilon Hufnagel) with Entomopathogenic Nematodes by Ganpati Jagdale

  • The black cutworm, Agrotis ipsilon (Hufnagel), is a polyphagous pest, feeding on almost all vegetables, many grain crops, ornamentals, turf grasses and weeds.
  • The plants damaged by black cutworms include beans, broccoli, cabbage, carrot, Chinese broccoli, Chinese cabbage, Chinese spinach, clover, corn, cotton, eggplant, flowering white cabbage, green beans, head cabbage, lettuce, mustard, potato, spinach, sugarcane, sweet potato, tomato, turnip, alfalfa, rice, sorghum, strawberry, sugarbeet, tobacco, bluegrass (Poa pratensis), curled dock (Rumex crispus); lambsquarters (Chenopodium album), yellow rocket (Barbarea vulgaris) and redroot pigweed (Amaranthus retroflexus).
  • There are five to nine larval instars that generally feed on seedlings at ground level by cutting off the stem causing a significant damage especially in newly planted fields. They also feed on roots and the below ground stem.
  • They can damage turfgrass by clipping off their blades and shoots.
  • The biological control agents including a bacterium Bacillus thuringiensis var. kurstaki, and entomopathogenic nematodes have a great potential against black cutworms.
  • Bacillus thuringiensis var. kurstaki produces a toxin that paralyzes the gut of the caterpillar.  This toxin does not kill the caterpillars quickly, but it does cause the caterpillars to stop feeding, which in turn reducing the intensity of the damage.
  • Since caterpillars of cutworms are highly mobile insects, the entomopathogenic nematodes with ambush type of foraging strategy can be used very effectively for the management of cutworms.
  • For example, Steinernema carpocapsae, is an ambusher nematode species that can control black cutworms very effectively if applied at a rate of 1 billion nematodes/acre on golf course greens.

How Entomopathogenic Nematodes Kill Black Cutworms

  • When the infective juveniles are applied to the soil surface or thatch layer, they start searching for their hosts, in this case caterpillares.
  • Once a caterpillar has been located, the nematode infective juveniles penetrate into the caterpillar body cavity via natural openings such as mouth, anus and spiracles.
  • Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae) from their gut in the caterpillar blood.
  • In the blood, multiplying nematode-bacterium complex causes septicemia and kills shore fly larvae usually within 48 h after infection.
  • Nematodes feed on multiplying bacteria, mature into adults, reproduce and then emerge as infective juveniles from the cadaver to seek new larvae in the potting medium/soil.

Kill leafminers (Liriomyza spp.) with Entomopathogenic Nematodes by Ganpati Jagdale

  • Leafminers (Liriomyza spp.) are considered as economically important polyphagous pests of many indoor vegetable crops and flowering plants.
  • Vegetable host crops included beans, beet, carrots, celery, cucumbers, eggplants, lettuce, melons, onions, peas, peppers, potatoes, squash and tomatoes.
  • Flowering host plants included ageratum, aster, calendula, chrysanthemum, dahlia, gerbera, gypsophila, marigold, petunia, snapdragon, and zinnia.
  • Leafminer maggots generally feed on leaf parenchyma tissues by tunneling/mining between the upper and lower epidermal leaf surfaces.
  • Adults generally feed on sap exuding from the punctures caused by maggots during mining.
  • Infested leaves appear stippled due to the punctures made by leafminers while feeding, mining and oviposition especially at the leaf tip and along the leaf margins.
  • Widespread mining and stippling on the leaves generally decreases the level of photosynthesis in the plant leading towards the premature leaf drop reducing the amount of shade, which in turn causes sun scalding of fruits.
  • Injuries caused by maggots on the foliage also allow entry of bacterial and fungal disease causing pathogens.
  • Life cycle of leafminers contains four stages including egg, maggot, pupa and adult.
  • Life cycle can be completed within 15-21 days depending upon the host and temperature.
  • Adult females lay eggs in leaf tissues, eggs hatch within 2-3 days into maggots, hatched maggots starts feeding immediately and become mature within 3-4 days. Mature larvae eventually cut through the leaf epidermis and move to the soil for pupation and adults emerge within 3 weeks of pupation in the summer.
  • Although, chemical insecticides are generally used to protect foliage from injury caused by leafminers, but development of insecticide resistance among leafminer populations is a major problem.
  • Insecticides also are highly disruptive to naturally occurring biological control agents, particularly parasitoids.
  • Therefore, biological control agents including Bacillus thuringiensis var. thuringiensis (Bt), parasitic wasps (Diglyphus begina, D. intermedius, D. pulchripes and Chrysocharis parksi) and entomopathogenic nematodes (Heterorhabditis spp, Steinernema carpocapase and S. feltiae) have been considered as alternatives to chemical pesticides.
  • For successful control of leafminers, entomopathogenic nematodes can be easily applied in water suspension as spray application on plant foliage.
  • Entomopathogenice nematodes including S. carpocapase and S. feltiae when applied at the rate of 5.3 X 108 nematodes/ha can cause over 64% mortality of leafminers but need at least 92% relative humidity.

How Entomopathogenic Nematodes kill leafminers

  • When the infective juveniles are applied as spray to plant foliage, they enter the leaf mines through the leaf miner feeding punctures or exit holes made by the adults.
  • Once inside the mine the nematodes swim to find a leafminer maggot, nematodes then penetrate into the maggot body cavity via natural openings such as mouth, anus and spiracles.
  • Infective juveniles of Heterorhabditis also enter through the intersegmental members of the larval cuticle.
  • Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae) from their gut in the maggot blood.
  • In the blood, multiplying nematode-bacterium complex causes septicemia and kills maggots usually within 48 h after infection.

For more information on the interaction between entomopathogenic nematodes and leafminers, please read following research and extension publications.

  • Hara, A.H., Kaya, H.K., Gaugler, R., Lebeck, L.M. and Mello, C.L. 1993. Entomopathogenic nematodes for biological control of the leafminer, Liriomyza trifolii (Dipt.: Agromyzidae).  Entomophaga 38, 359-369.
  • Head, J. and Walters, K.F.A. 2003.  Augmentation biological control utilising the entomopathogenic nematode, Steinernema feltiae, against the South American Leafminer, Liriomyza huidobrensis. Proceedings of the 1st International Symposium on Biological Control, (Hawaii, USA, 13-18 January 2002). USDA Forest Service, FHTET-03-05, 136-140.
  • Olthof, T.H.A. and Broadbent, A.B. 1992.  Evaluation of steinernematid nematodes for control of a leafminer, Liriomyza trifolii, in greenhouse chrysanthemums. Journal of Nematology 24, 612.
  • Tong-Xian Liu, Le Kang, K.M.Heinz, J.Trumble. 2008. Biological control of Liriomyza leafminers: progress and perspective. CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2009, 4, No. 004, 16 pp.
  • Williams, E.C. and Walters, K.F.A. 1994.  Nematode control of leafminers: Efficacy, temperature and timing.  Brighton Crop Protection Conference - Pests and Disease. 1079-1084.
  • Williams, E.C. and MacDonald, O.C., 1995.  Critical factors required by the nematode Steinernema feltiae for the control of the leafminers Liriomyza huidobrensis, Liriomyza bryoniae and Chromatomyia syngenesiae.  Annals of Applied Biology. 127, 329-341.
  • Williams, E.C. and Walters, K.F.A. 2000.  Foliar application of the entomopathogenic nematode Steinernema feltiae against leafminers on vegetables. Biocontrol Science and Technology 10, 61-70.

Kill fungus gnats using biological control agents: Insect-parasitic nematodes by Ganpati Jagdale

  • Several fungus gnat species including Bradysia coprophila, B. impatiens and B. difformis are considered economically important indoor and greenhouse pests in Europe and the US.
  • Fungus gnat flies are black or gray in color with clear wings, relatively small (3-4 mm) in size and commonly associated with compost and natural soils with high organic contents.
  • You can see these hopping flies when you water your plants.
  • Fungus gnat maggots (larvae) are white-bodied with black heads and can be found just under the surface of the potting medium/soil.
  • These maggots primarily feed on fungi and organic matter but they can also cause a serious damage to many ornamental plants.
  • Maggots often chew or strip plant roots and tunnel stems affecting water and nutrient absorption in severely injured plants resulting in lost vigor, turn off-color and eventually death.
  • Maggots are also capable of transmitting fungal pathogens (Fusarium, Phoma, Pythium and Verticillium) during feeding.
  • Adult flies are nuisance to people and disseminate fungal spores from plant to plant as they disperse through the greenhouse.
  • Females often laying over 1000 eggs in a lifetime on the media surface and completing egg-to-egg life cycle within 20-25 days at 20-25oC.
  • Continuous and overlapping generations of fungus gnats in the greenhouse have made most control strategies difficult.
  • Currently, most growers rely on insecticides to manage fungus gnats in floriculture.
  • However, use of these insecticides is restricted due to their environmental pollution and human health concerns, development of resistance to pesticides and removal of some of the most effective products from the market.
  • Biological control agents including Bacillus thuringiensis (Bt), the predatory mite, Hypoaspis miles and entomopathogenic nematodes have been used as alternatives to chemical pesticides.
  • The entomopathogenic nematodes species including Heterorhabditis bacteriophora GPS11 strain, H. indica LN2 strain and Steinernema feltiae UK strain have a potential to use as biocontrol agents against fungus gnats.
  • These nematodes kill both maggots (larvae) and pupae, but the second and fourth stages are most susceptible than pupae.
  • Nematodes are generally applied in water suspension as spray applications to the surface of plant growing medium to target larval and pupal stages.
  • The potting medium (Ball-mix, Nursery-mix or Pro-mix) can influence the survival, persistence and efficacy of entomopathogenic nematodes in greenhouse production.
  • In the Nursery-mix, H. bacteriophora can survive longer and perform better than H. indica, H. marelatus Oregon, H. zealandica X1 and Steinernema feltiae against fungus gnats.
  • In the Pro-mix, only H. indica have performed better than all other nematode species that tested against fungus gnats.
  • Application of S. feltiae can cause 40% reduction in fungus gnat population in Ball-mix, 50% in Metro-mix and 56% in Pro-mix, but only 27% in the Nursery-mix.
  • In the greenhouse, temperature can influence efficacy of nematodes. For example, H. bacteriophora and H. indica can survive and cause very high mortality of fungus gnats at warmer (above 25oC) temperatures whereas S. feltiae is generally effective against fungus gnats at cooler (below 25oC) temperatures.
  • Application of an appropriate concentration of nematodes is a crucial step in the cost effective control of fungus gnats in greenhouse production.
  • Generally, application of one billion infective juveniles of H. bacteriophora, H. indica or S. feltiae per acre can kill over 50% fungus gnats in greenhouse productions.

How entomopathogenic nematodes kill fungus gnats

  • When the infective juveniles are applied to the surface of plant growing medium, they start searching for hosts, in this case fungus gnat maggots (larvae) and pupae.
  • Once a maggot/pupa has been located, the nematode infective juveniles penetrate into the maggot body cavity via natural openings such as mouth, anus and breathing pores called spiracles.
  • Infective juveniles of Heterorhabditis spp also enter through the intersegmental members of the maggot/pupal cuticle.
  • Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae) from their gut in the fungus gnat blood.
  • Multiplying nematode-bacterium complex causes septicemia and kills the host usually within 48 h after infection.
  • Nematodes feed on multiplying bacteria, mature into adults, reproduce and then emerge as infective juveniles from the cadaver to seek new maggots in the potting medium/soil.

Nematodes are now commercially available from many suppliers distributed throughout in the USA.

For more information on biological control of fungus gnats, please read following research papers/book chapters:

  • Binns, E.S., 1973.  Fungus gnats (Diptera: Mycetophilidae, Sciaridae) and the role of mycophagy in soil: a review. Rev. Ecol. Biol. Sol. 18, 77-90.
  • Chambers, R.J., Wright, E.M., Lind, R.J., 1993.  Biological control of glasshouse sciarid larvae (Bradysia spp.) with the predatory mite, Hypoaspis miles on Cyclamen and Poinsettia. Biocontrol Sci. Technol. 3, 285-293.
  • Ecke, P.Jr., Faust, J.E., Williams, J., Higgins, A., 2004.  The Poinsettia Manual. Ball Publishing, The Paul Ecke Ranch, Encinitas, California, USA.
  • Freeman, P., 1983.  Sciarid flies, Diptera; Sciaridae. Handbooks for the identification of British insects 9, Part 6. London, Royal Entomol. Soc. pp 68.
  • Gillespie, D.R., Menzies, J.G., 1993.  Fungus gnat vector Fusarium oxysporum f. sp. radicislycopersici.  Ann. Appl. Biol. 123, 539-544.
  • Gouge, D.H., Hague, N.G.M., 1994.  Control of sciarids in glass and propagation houses with Steinernema feltiae. Brighton Crop Protection Conference: Pest Dis. 3, 1073-1078.
  • Gouge, D.H., Hague, N.G.M., 1995.  Glasshouse control of fungus gnats, Bradysia paupera, on fuchsias by Steinernema feltiae. Fundam. Appl. Nematol. 18, 77-80.
  • Grewal, P.S., Richardson, P.N., 1993.  Effects of application rates of Steinernema feltiae (Nematoda: Steinernematidae) on control of the mushroom sciarid fly, Lycoriella auripila (Diptera: Sciaridae).  Biocontrol Sci. Technol. 3, 29-40.
  • Grewal, P.S., Tomalak, M., Keil, C.B.O., Gaugler, R., 1993. Evaluation of a genetically selected strain of Steinernema feltiae against the mushroom sciarid fly, Lycoriella mali. Ann. Appl. Biol. 123, 695-702.
  • Harris, M.A., Oetting, R.D., Gardner, W.A., 1995.  Use of entomopathogenic nematodes and new monitoring technique for control of fungus gnats, Bradysia coprophila (Diptera: Sciaridae), in floriculture. Biol. Control 5, 412-418.
  • Jagdale, G. B., Casey, M. L., Grewal, P. S. and Lindquist, R. K. 2004.  Application rate and timing, potting medium and host plant on the efficacy of Steinernema feltiae against the fungus gnat, Bradysia coprophila, in floriculture. Biol. Contrl. 29: 296-305.
  • Jagdale, G. B., Casey, M. L., Grewal, P. S. and Luis Cañas. 2007.  Effect of entomopathogenic nematode species, split application and potting medium on the control of the fungus gnat, Bradysia difformis (Diptera: Sciaridae), in the greenhouse at alternating cold and warm temperatures. Biol. Control. 43: 23-30.
  • Kim, H.H., Choo, H.Y., Kaya, H.K., Lee, D.W., Lee, S.M., Jeon, H.Y., 2004.  Steinernema carpocapsae (Rhabditida: Steinernematidae) as a biological control agent against the fungus gnat Bradysia agrestis (Diptera: Sciaridae) in propogation houses. Biocontrol Sci. Technol. 14, 171-183.
  • Lindquist R., Piatkowski J. 1993. Evaluation of entomopathogenic nematodes for control of fungus gnat larvae. Bull. Int. Organiz. Biol. Integr. Control Noxious Animals and Plants. 16, 97-100.
  • Lindquist, R.K., Faber, W.R., Casey, M.L., 1985.  Effect of various soilless root media and insecticides on fungus gnats.  HortScience. 20, 358-360.
  • Menzel, F., Smith, J.E., Colauto, N.B., 2003.  Bradysia difformis Frey and Bradysia ocellaris (Comstock): two additional neotropical species of black fungus gnats (Diptera : Sciaridae) of economic importance: a redescription and review. Ann. Entomol. Soc. Am. 96, 448-457.
  • Nielsen, G. R., 2003. Fungus gnats. http://www.uvm.edu/extension/publications/el/el50.htm
  • Oetting, R.D., Latimer, J.G., 1991.  An entomogenous nematode Steinernema carpocapsae is compatible with potting media environments created by horticultural practices. J. Entomol. Sci. 26, 390-394.
  • Olson, D.L., Oetting, R.D., van Iersel, M.W., 2002.  Effect of soilless media and water management on development of fungus gnats (Diptera: Sciaridae) and plant growth. HortScience. 37: 919-923.
  • Richardson, P.N., Grewal, P.S., 1991.  Comparative assessment of biological (Nematoda: Steinernema feltiae) and chemical methods of control of mushroom fly, Lycoriella auripila (Diptera: Sciaridae).  Biocontrol Sci. Technol. 1, 217-228.
  • Tomalak, M., Piggott, S. and Jagdale, G. B. 2005.  Glasshouse applications. In: Nematodes As Biocontrol Agents. Grewal, P.S. Ehlers, R.-U., Shapiro-Ilan, D. (eds.). CAB publishing, CAB International, Oxon. Pp 147-166.
  • Wilkinson, J.D., Daugherty, D.M., 1970.  Comparative development of Bradysia impatiens (Diptera: Sciaridae) under constant and variable temperatures. Ann. Entomol. Soc. Am. 63, 1079-1083.