Serratia marcescens found in eggs of Heliothis zea: Tests against Trichoplusia ni

Abstract

The red strain ofSerratia marcescens(Bizio) has been isolated from healthy, diseased, or dead field-collected insects, but it is most frequently reported as a pathogen of insectary-reared insects. In this study, we determined the path of transmission ofS. marcescensin adultHeliothis virescens(F.) to the next generation and compared longevity of infected and uninfected adults. Our results show thatS. marcescenscan be present on or within eggs produced byS. marcescens-infected pairs. Highest external contamination and/or internal infection of surface sterilized eggs from moths fed an aqueous solution of 10% honey contaminated withS. marcescens(4 × 108bacterial cells/ml) was 45% and internal infection of eggs from the same group of moths was 19%. The highest percentage of adults producing eggs contaminated and/or infected withS. marcescenswas 70% and the highest percentage producing internally infected eggs was 17%. The highest percentage of total adult mortality at day 10, in bacterial treatments, was 90.1% and in the controls was 15%. Living infected moths are usually asymptomatic, but typically become red postmortem. We demonstrated thatS. marcescenscan be transmitted both vertically (genetic transmission; the passage of pathogen from one host generation to the next in or on egg) and horizontally (transmission of pathogen between insects at any age after birth) inH. virescens,and that the bacterium has detrimental effects on adult longevity. We point out in this paper thatS. marcescenshas been frequently reported from poor quality insectary-rearedH. virescens(poor vigor and high mortality). This insect which is commonly used for a host of beneficial endoparasitoids, production of viruses and protozoa, and testing various biological control agents, must be pathogen free (such asS. marcescens) to provide quality biological control agents or meaningful data.