Allee Effect in the Infection Dynamics of the Entomopathogenic Fungus Beauveria bassiana (Bals) Vuill. on the Beetle, Mylabris pustulata

Abstract

Successful infection by Beauveria bassiana as with all other entomopathogenic fungi, is accomplished only at a high conidial dose while, theoretically, a single conidium should be sufficient. Indeed, this is a major deterrent in its use as a biocontrol agent. High pathogen load for infection is required by organisms which display 'Allee' effect. In such organisms, a threshold exists for pathogen dose, below which no infection can be caused. B. bassiana has a semelparous life cycle and, therefore, its infection dynamics are expected to conform to the mass action principle with a linear relationship between dose and successful infection observable as mortality of the insect. Whether the need for a high conidial dose to induce insect mortality by B. bassiana is due to the operation of Allee effect was examined. A sample of 34 isolates was bioassayed on Mylabris pustulata (Coleoptera: Meloidae) at four conidial concentrations. With more than half of the isolates in the sample, the lowest dose tested (10(4) conidia/insect) did not cause insect mortality. Thus, a threshold pathogen load is required to cause successful infection. In these isolates, the dose-mortality relationship was sigmoid. Allee effect is thus identified in the infection dynamics of B. bassiana-M. pustulata system. The isolates that induced mortality at the lowest dose tested are concluded to be highly virulent with a lower threshold dose required for successful infection. With some isolates, at high conidial dose, the infection rate decreased either due to a decrease in the proportion of insects showing mycosis, to the speed of death, or both. Such a response could result from intra scramble competition arising from overload of pathogen at very high dose.

Allee Effects May Slow the Spread of Parasites in a Coastal Marine Ecosystem

“…Several studies have empirically documented dose-dependent establishment, incubation time, and host mortality for microparasites (Agnew and Koella 1999;McLean and Bostock 2000;Hughes et al 2004;Devi and Rao 2006), which are processes that may lead to a demographic Allee effect in the population dynamics of the parasite (Regoes et al 2002). Nonetheless, for macroparasites, we are unaware of empirical examples of Allee effects, including mate limitation or other effects.…”

Interactions between the fungal pathogen Beauveria bassiana and three species of coccinellid: Harmonia axyridis, Coccinella septempunctata and Adalia bipunctata

“…A number of recent publications have shown that B. bassiana isolates are very genetically variable (Aquino de Muro et al 2003Estrada et al 2007;Ormond 2007), and concomittantly highly phenotypically variable in parameters such as virulence (Bidochka et al 2002;Devi and Rao 2006;Talaei-Hassanloui et al 2006). The natural enemy escape hypothesis is often used as an explanation for the rapid establishment and proliferation of an invasive alien species; the geographical displacement of the species results in escape from predators and parasites and so gives the invading species an advantage over native species that are attacked by a suite of indigenous natural enemies (e.g.…”

Fungi against insects and contrariwise as biological control models

“…Soil plays a key role in forming insect populations hence the inhabiting EPF. The communities of EPF differ from one location to another, for example, populations of EPF in the arable soils seem to be different than those in barren lands (Devi et al 2006;Garrido-Jurado et al 2011). Quesada-Moraga et al (2007 detected EPF populations in a wide area of Spain, the EPF were isolated from 175 soil samples out of the 244, and only 2 species were found, B. bassiana and M. anisopliae.…”