Initiation of fungal epizootics in diamondback moth populations within a large field cage: proof of concept for auto‐dissemination

Abstract

Adult diamondback moths (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), inoculated with the fungus Zoophthora radicans , were released within a large field cage containing DBM-infested potted broccoli plants. Larvae and pupae on exposed and caged control plants were examined on five occasions over the next 48 days for evidence of Z. radicans infection. Infected larvae were first detected on exposed plants 4 days after the initial release of adults, and after 48 days the infection level reached 79%. Aerially borne conidia were a factor in transmission of the fungus. Infection had no effect on possible losses of larval and adult cadavers due to scavengers in field crops. In a trial to measure the influence of infection on dispersal, twice as many non-infected as infected males were recaptured in pheromone traps, although the difference in cumulative catch only became significant 3 days after release of the males. In a separate experiment, when adult moths were inoculated with Beauveria bassiana conidia and released into the field cage, DBM larvae collected from 37 of 96 plants sampled 4 days later subsequently died from B. bassiana infection. The distribution of plants from which the infected larvae were collected was random, but the distribution of infected larvae was clustered within the cage. These findings suggest that the auto-dissemination of fungal pathogens may be a feasible strategy for DBM control, provided that epizootics can be established and maintained when DBM population densities are low.

Entomopathogenic fungi and insect behaviour: from unsuspecting hosts to targeted vectors

“…The insects that are inoculated can either be the pest species or non-target insects that act as vectors of the pathogen. Assisted auto-dissemination works by attracting an insect into an inoculation device where it becomes contaminated with the infective conidia before returning to the crop and disseminating the pathogen to pest insects (Vega et al 2000;Vickers et al 2004). Assisted-autodissemination has been widely assessed for a number of insect and fungal species and has several advantages over the mass application of entomopathogenic fungi, the benefits include: (1) it is highly efficient, especially when incorporating a target specific pheromone, (2) it can be species specific, (3) dissemination devices are simple to construct and maintain, (4) it is cost effective as the ratio of fungal inoculum to hosts is low and, (5) contaminated insects will return to their habitats, therefore dispersing the pathogen (Vega et al 2000;Yasuda 1999).…”

Biological control of the diamondback moth,Plutella xylostella: A review

“…Zoophthora (0/Erynia ) radicans , an important entomopathogenic fungus isolated from DBM, is reported to cause epizootics under favorable environmental conditions and can reduce local populations to zero (Ooi 1981;Riethmacher et al 1992). The moths infected/ contaminated with Z. radicans can serve as a source of fungal inoculum in the field and airborne conidia lead to epizootics as a result of auto-dissemination in DBM populations (Vickers et al 2004). Although infected insects can survive for some time, a reduction in feeding damage may occur sooner.…”

“…It involves the attraction of male moths in response to synthetic female sex pheromone into specially designed inoculation chambers containing infective fungal spores. Once inside the chamber they become contaminated with conidia and then return to the crop, disseminating the pathogen in the local population (Vickers et al 2004). Intensive research is needed to determine the potential and efficacy of other entomopathogens.…”

“…The DBM is multivoltine with four to 20 generations per year in temperate and tropical regions, respectively (Harcourt 1986;Vickers et al 2004). Each female can lay over 200 eggs mainly on the upper leaf surface (Talekar et al 1994;Justus et al 2000).…”

Spatiotemporal distribution and impact of diamondback moth parasitoids in the Dakar Niayes in Senegal

“…This insect species is a problem in the tropical and subtropical countries where cabbage is grown all year round. Weather conditions hightly favourable for its biological development, associated with a high reproduction rate, result in more than 20 generations of DBM per year (Vickers et al, 2004).…”