Immune Response of Mormon Crickets That Survived Infection byBeauveria bassiana

Robert B Srygley,Stefan T Jaronski

doi:10.1155/2011/849038

Abstract

Beauveria bassiana(Fungi: Ascomycota) is an entomopathogenic fungus that serves as a biological control agent of Mormon cricketsAnabrus simplexHaldeman (Orthoptera: Tettigoniidae) and other grasshopper pests. To measure the dose-dependent response of Mormon crickets to fungal attack, we appliedB. bassianastrain GHA topically to adults using doses of 5.13 × to 1.75 × conidia in sunflower oil, with oil only as a control. After three weeks, we assessed the survivors' hemolymph for fungal cells, active phenoloxidase (PO), and lysozyme. Mortality increased and body mass of survivors decreased with conidial dose. survivors' PO activity was elevated to the same level independent of dose. Those with fungal cells visible in their hemolymph did not differ in PO activity from those with clear hemolymph. We conclude that circulating PO may be an important enzymatic defense againstBeauveriainfection and that it is associated with attempted clearing ofBeauveriablastospores and hyphae from Mormon cricket hemolymph.

Highlights

Nomadic insects risk contact with fungal pathogens [1]
We investigate circulating PO and lysozyme titres in adult Mormon crickets that have successfully defended themselves against invasion from topically applied Beauveria bassiana strain GHA
Mortality at 21 days ranged from 22% to 80% and increased with the dose of B. bassiana applied to the cuticle (Table 1) with an LD50 estimate of 6.46 × 105 conidia per insect

Summary

Introduction

A long-horned grasshopper or katydid, form bands and march across western United States grasslands seeking food, salt, and oviposition sites (Figure 1, [2, 3]). Wingless, they must walk, which increases the risk of contacting insect-pathogenic ascomycetous fungi, such as Beauveria spp. and Metarhizium spp., on plants or soil [4]. The ability of the fungus to infect an insect depends on its ability to adhere and penetrate the exoskeleton, resist the insect’s hemolymph-borne defenses, and grow rapidly [5]. Death of the host may result from competition with the pathogen for nutrients, mechanical damage resulting from hyphal growth, and fungal toxins [5]

Methods

Results

Conclusion