Thrips - Biological control of pests
Fig. 1: Anthocorid or Pirate bug (Orius laevigatus)
attacking a thrips larvae (photo: U Wyss, Entofilm)
Fig. 2: Amblyseius degenerans attacks a thrips larva (photo: U Wyss, Entofilm)
Fig. 3: Phytoseiid mite (Neoseiulus sp.)
Fig. 4: Predatory thrips (Franklinothrips vespiformis) on an adult Parthenothrips dracaenae (photo: U Wyss, Entofilm)
Predatory thrips (Franklinothrips vespiformis) feeds on a thrips larva
Fig. 6: Thribobius sp. attacks a Hercinothrips larva (photo: U Wyss, Entofilm)
Fig. 7: Larval endoparasitoid (Ceranisus menes) - adult
Fig. 8: Larval endoparasitoid (Ceranisus menes) - parasitized pupae
Fig. 9: Metarhizium anisopliae infected adult thrips
Fig. 10: Pronotum of Thrips tabaci with calcufluor stained hyphae of Lecanicillium longisporum (Verticillium lecanii)
Fig. 11: Abdomen of Chirothrips guillarmodi strongly infected with nematods
Fig. 12: Pregenitalregion of abdomen of Chirothrips guillarmodi with embryonic stages of roundworm parasites (Nematoda)
Biological control of thrips
Several species of thrips are a major constraint to productivity of wide array of crops including staple food crops, high value vegetables, oil seed crops, cash crops and ornamentals both in the open field and the greenhouses. They inflict direct damage due to their feeding and indirect damage due to their ability to transmit tospoviruses. Due to their cryptic feeding behavior effective targeting of thrips with chemical pesticides has been a challenge, resulting in excessive use of chemical pesticides. The short generation time and excessive pesticide use has resulted in rapid development of resistance to insecticides (Robb et al. 1995). Further there is associated risk of harmful pesticide residues and emergence of secondary pests in an insecticide based thrips and tospovirus management approach. Biological control methods offer a viable and sustainable alternative for management of thrips and thrips-transmitted tospoviruses. An effective biological control strategy needs to target the various development stages of thrips observed above and below ground.
Biological control options available for thrips control can be broadly grouped into predators, parasitoids, entomopathogenic fungi and entomopathogenic nematodes.
Although diverse groups of arthropods have been identified as predators of thrips (Ananthakrishnan 1979; Riudavets 1995), groups that have potential for use in biological control of thrips include Anthocorid bugs; predatory mites and some predatory thrips (Riudavets 1995). However most of the predators are generalist, capable of predating a wide range of insects and mites.
The Anthocorid or Pirate bugs, especially the insect belonging to the genera Orius Wolff, Anthocoris Fallen, Montandoniola etc are active generalist predators used in biological control programs for thrips (Riudavets 1995). They are very effective against the larval stages of the thrips, and to some extent they also predate on the eggs. In East African cropping systems Orius albidipennis (Reuter), Orius tantillus (Motschulsky) and Orius thripoborus (Hesse) were the most abundant and broadly distributed among the species belonging to genus Orius (Hernandez & Stonedahl, 1999). A key to identification of economically important species of Orius in East Africa has been published by Hernandez & Stonedahl (1999). Globally Anthocorid species such as Orius albidipennis, Orius armatus, Orius insidiosus,Orius laevigatus, Orius majuscules, Orius minutes, Orius strigicollis and Orius tristicolor are commercially available and used in augmentative biological control targeting thrips (van Lenteren 2012).
Among the predatory mites, species belonging to Phytoseiidae such as Amblyseius swirskii, Amblyseius limonicus; Amblyseius degenerans; Neoseiulus barkeri, Neoseiulus cucumeris and Typhlodromips montdorensis have been used commercially for thrips control in augumentative biological control programs (van Lenteren 2012). Neoseiulus cucumeris is commercially available for thrips management in East Africa. The predatory mites are effective predators against both the egg and larval stages of thrips (van Houten et al. 1995).
Unlike the Anthocorid bugs and predatory mites, use of predatory thrips belonging to Aeolothripidae and others such as Scolothrips and Karnyothrips are limited. Species such as Franklinothrips vespiformis, Franklinothrips megalops have been used in classical and conventional biological programs and some are available commercially. Further thrips species such as Scolothrips sexmaculatus, Karnyothrips melaleucus and Karnyothrips flavipes are potential biological control options for thrips (van Lenteren 2012).
All parasitoids of thrips belong to the superfamily Chalcidoidea in the Families Eulophidae, Trichogrammatidae and Mymaridae. Based on their mode of parasitism, they can be broadly grouped as larval solitary endoparasitoids (Eulophidae) or egg parasitoids (Mymariidae, Trichogrammatidae) (Loomans & van Lenteren 1995).
Thrips control-larval endoparasitoids-entedonine
In Eulophidae, many entedonine parasitoids (Hymenoptera: Chalcidoidea: Eulophidae: Entedoninae) promise to be potential biological control agents of pest thrips. They are minute (0.5 to 1.1 mm), solitary endoparasitoids of larval stages of thrips, although sometimes the prepupae and/or pupae of thrips may be attacked, and can be found in four closely related genera: Ceranisus, Goetheana, Thripobius and Entedonomphale (Boucek 1976). Currently 27 species are described, parasitizing over 70 species of Thysanoptera (Loomans & van Lenteren 1995). In Africa, so far eight larval endoparasitoids belonging to Entedoninae: Eulophidae including Ceranisus menes, Ceranisus femoratus; Entedonomphale esenini, Entedonomphale lermontovi; Thripobius javae, Thripobius hirticornis and Goetheana shakespeari and Goetheana incerta have been recorded (Loomans & van Lenteren 1995; Tamò et al. 1993; Triapitsyn 2005). Among these classical biological control efforts with Ceranisus femoratus for the management of Bean Flower thrips has shown promise (Tamò et al. 1993).
Egg parasitoids of thrips mostly belong to the genus Megaphragma (Trichogrammatidae) and one species in the genus Polynema (Mymaridae). Very small size of these parasitoids hampers their collection and efficacy evaluation. Egg parasitoids have been only observed on thrips belonging to thripidae were oviposition is endophytic (Loomans & van Lenteren 1995). In Africa, three egg parasitoids including Megaphragma sp., Megaphragma mymaripennae and Oligosita sp. have been recorded. Records of thrips parasitoids from Africa are relatively low as compared to other parts of the world. However this might be more due to lack of extensive information on their diversity in Africa, and not the actual diversity.
Among the biopesticide available for insect control, the entomopathogenic fungi and nematodes have great potential for use in thrips management due to their mode of action and habitats where they are effective. The amenability for their mass culturing is also an advantage with both entomopathogenic fungi and nematodes.
Entomopathogenic fungi and nematods
The use of entomopathogenic fungi for thrips holds a lot of promise due to its contact infectivity and ability to penetrate through the cuticle (Goettel & Inglis 1997; Butt & Goettel 2000). Metarhizium anisopliae (Vestergaard 1995; Ekesi et al. 1998, 2000; Maniania et al. 2003; Niassy et al. 2012), Beauveria bassiana (Castineiras et al. 1996a,b; Gao et al. 2012), Paecilomyces fumosoroseus (Castineiras et al. 1996), Lecanicillium (=Verticillium) lecanii (Saito 1992; Helyer 1993, Schreiter et al 1994) are potential entomopathogenic fungi evaluated for thrips control. Optimization of formulation and application technology, enhancement of shelf and environmental durability are very essential to ensure success with entomopathogenic fungi for thrips management. In Africa, a strain of Metarhizium anisopliae has been commercialized under the trade name Campaign ® for thrips control (Ekesi et al. 2011).
Entomopathogenic and parasitic nematode
Entomopathogenic nematodes (EPNs) belonging to families Steinernematidae and Heterorhabditidae are potentially effective biocontrol agents of soil dwelling stages of the thrips (Chyzik et al. 1996; Ebssa et al. 2004; Arthurs & Heinz, 2006; Sims et al. 2012). The entomoparasitic nematode Thripinema nicklewoodi Siddiqi and Thripinema fuscum infects above ground thrips stages and causes sterility of female hosts (Arthurs & Heinz 2003, 2006).
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