The pathogenicity of Vairimorpha necatrix (Microspora: Microsporidia) against the tomato moth, Lacanobia oleracea (Lepidoptera: Noctuidae) and its potential use for the control of lepidopteran glasshouse pests

Abstract

A droplet feeding technique was used to feed known amounts of Vairimorpha necatrix (Kramer) spores to larvae of the tomato moth, Lacanobia oleracea (L) in order to assess the susceptibility of this lepidopteran pest to the pathogen. All first- to fourth-instar larvae died as a result of ingesting 1000 or more V necatrix spores. Two forms of death were observed, which were dependent on the dose and the age of the insect when treated. For first-instar larvae, rapid death (within 6days of dosing) occurred after ingestion of 2000 spores, whereas lower doses resulted in a proportion of larvae dying from chronic infection (microsporidiosis). For more advanced stages, increasing spore doses were required to give rapid death, such that a dose of 200,000 spores was needed to give 80% mortality within 6 days for third-instar larvae. Rapid death was not observed in fourth- to sixth-instar larvae. In all cases successful pupation and adult emergence were much reduced compared with non-infected larvae. Suspensions of V necatrix were sprayed on to tomato (Lycopersicon esculentum Mill) plants maintained in small glasshouses prior to infestation of the plants with L oleracea larvae. The numbers and biomass of pest larvae retrieved from the plants sprayed with V necatrix were significantly reduced by up to 40% and 70%, respectively, compared with plants sprayed with water (control). Similarly, plants sprayed with V necatrix showed a reduction in damage of up to 45% compared with the control plants.

Infection by the microsporidium Vairimorpha necatrix (Microspora: Microsporidia) elevates juvenile hormone titres in larvae of the tomato moth, Lacanobia oleracea (Lepidoptera: Noctuidae)

“…Therefore it could be advantageous to the parasite to extend the larval development of the host, possibly resulting in gigantism of the host, and allowing the microsporidium to maximise the number of spores it can produce for transmission when the host dies, as predicted by Obreski (1975). Extended larval development of the host, and gigantism, are common features of microsporidian infections in Lepidoptera (Gaugler and Brooks, 1975;Mitchell and Cali, 1994;Henn and Solter, 2000), and has been shown in L. oleracea larvae infected with V. necatrix in this present study and in previous work (Down et al, 2004).…”

“…Infected larvae were kept at 20°C, 65% relative humidity and 16L:8D. Vairimorpha necatrix spores were harvested three to four weeks later as described previously (Down et al, 2004). Briefly, infected larvae were dissected and the body cavities rinsed with tap water.…”

“…Mature spores of V. necatrix are only released into the environment when the host larvae dies and its body disintegrates or is eaten (Maddox et al, 1998). In many cases infection by V. necatrix markedly extends the developmental period of the host, and sometimes results in gigantism (Gaugler and Brooks, 1975;Mitchell and Cali, 1994;Henn and Solter, 2000;Down et al, 2004). Some authors (Obreski, 1975;Blaser and Schmid-Hempel, 2005) have suggested that this extended development period may be adaptive and serve to allow the microsporidium to produce a greater number of spores over hosts that more closely follow a normal developmental pattern.…”

“…The microsporidium Vairimorpha necatrix is an intracellular parasite, which has been shown to infect a number of lepidopteran species under laboratory conditions (Maddox and Sprenkel, 1978;Fuxa, 1981;Maddox et al, 1981;Wilson, 1984Wilson, , 1986Down et al, 2004). Host larvae are usually fatally infected.…”

Prevalence and impact of the microsporidium Thelohania solenopsae (Microsporidia) on wild populations of red imported fire ants, Solenopsis invicta, in Louisiana

“…They typically produce chronic, sublethal infections causing prolong larval development; reduced pupal weight and adult reproduction; increased susceptibility to other pathogens and toxins; and they can alter host behavior (e.g., Windels et al, 1976;Fuxa, 1979Fuxa, , 1981Solter et al, 1990;Tanada and Kaya, 1993;Mitchell and Cali, 1994;Inglis et al, 2003;Reardon et al, 2004;Shi and Njagi, 2004). In some instances, they can cause severe diseases and high mortality rates (e.g., Maddox et al, 1981;Down et al, 2004;Goertz et al, 2004). Kohler and Hoiland (2001) suggested that a microsporidian disease was a key factor controlling the population dynamics of a caddysfly (Brachycentrus americanus Banks), while Tanada and Kaya (1993) proposed that microsporidia show potential for being used in biological control.…”