Exclusion techniques reveal significant biotic mortality suffered by Asian citrus psyllid Diaphorina citri (Hemiptera: Psyllidae) populations in Florida citrus

Abstract

Management of ‘huanglongbing’ (HLB) or the Asian form of citrus greening disease caused by the bacterium, Candidatus Liberibacter asiaticus, and spread by Diaphorina citri Kuwayama depends largely on the management of the vector insect. Seventeen experiments conducted during 2006–2007 included D. citri colonies initiated with eggs or first instar nymphs on young shoots protected with sleeve cages, sticky barriers or left unprotected through adult emergence to assess the relative impact of abiotic and biotic factors on psyllid populations. Temperatures dropped to 0 °C and killed most of the shoots and nymphs in February 2007. Spiders (Araneae) and insects in the families Coccinellidae, Blattellidae, Chrysopidae, Formicidae, Syrphidae, Anthocoridae and Miridae were observed on colonies or caught in sticky barriers. The ladybeetles Olla v-nigrum, Curinus coeruleus, Harmonia axyridis, and Cycloneda sanguinea, the cockroach Blattella asahinai, lacewings, Ceraeochrysa sp. and Chrysoperla sp., and spiders were most often encountered. Parasitism by Tamarixia radiata provided 1–3% nymphal mortality in relation to adult emergence although a maximum of about 25% was observed. Net reproductive rate ( R 0), based on observed survivorship and temperature-dependent fecundity data was estimated to be 5- to 27-fold higher in the colonies protected with full cages compared to the unprotected colonies except during the freeze. At the extreme, R 0 was estimated in caged colonies at 125–285 in Jun 2006 whereas all nymphs disappeared in the unprotected colonies. Intermediate results were observed in colonies protected with sticky barriers or coarse mesh cages. These findings suggest that biotic factors play a vital role in regulating populations of D. citri. Their elimination through reckless pesticide use could increase pest pressure and enhance the spread of the disease. Therefore, integrated control programs based on conservation of natural enemies of D. citri through judicious use of insecticides and releases of new parasitoids are needed for sustainable management of pest and disease.