Page | 242 IRCHLB Proceedings Dec. 2008: www.plantmanagementnetwork.org 6.10 Effects of host plant on fitness of the Asian citrus psyllid, Diaphorina citri Tsagkarakis A.E. and Rogers M.E. University of Florida, IFAS, Citrus Research and Education Center, Lake Alfred, FL, USA. The reproductive biology of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is closely tied to the availability of new leaf flush for egg laying and subsequent development of psyllid nymphs. Increases in the psyllid population are thus most evident during periods of abundant new flush. However, what is not well understood are the varying effects of the host plant on psyllid fitness that may affect the magnitude of the increase or decrease in psyllid populations. The host range of D. citri includes many citrus and close citrus relatives. While there are many observations about preferred hosts of D. citri (Halbert and Manjunath 2004), only a few comparative laboratory studies have been conducted to date that specifically address suitability of different host plants on psyllid fitness under controlled conditions. In one study, Tsai & Liu (2000) examined the biology of D. citri on four host plants, orange jasmine (Murraya paniculata (L.) Jack), rough lemon (Citrus jambhiri Lushington), sour orange (Citrus aurantium L.), and grapefruit (Citrus × paradisi Macfad.). In this study, grapefruit was determined to be the best host, followed by the other plant species tested, among which there was no statistical difference. A second study, Nava et al. (2007) compared the duration and viability of psyllid egg and nymphal stages, sex ratio, fecundity and longevity on Rangpur lime (Citrus limonia), orange jasmine (Murraya paniculata) and Sunki mandarin (Citrus sunki) across a range of temperatures. Nymphal viability was lower on mandarin than on the other hosts evaluated while overall nymphal development was highest on C. limonia and M. paniculata. Fecundity was highest on M. paniculata. No other detailed comparative studies have been conducted on the effect of host plants on the fitness of D. citri, especially with regards to commercially grown citrus varieties in Florida. As part of a larger project investigating the effects of host plant quality on psyllid fitness, fitness of psyllids was examined when completing development on various citrus rootstock species commonly used in Florida citrus production. Here we report our intial findings comparing psyllid fitness on two rootstock species, sour orange (Citrus aurantium L.) and Cleopatra mandarin (Citrus reticulata Blanco). Previously, we have observed marked differences in psyllid colonization of these two rootstock species when provided as host plants for laboratory maintained colonies of D. citri. Psyllids were observed to readily colonize C. aurantium whereas little or no development was believed to occur on C. reticulata. The fitness of D. citri when reared on C. aurantium and C. reticulata was determined by evaluating the effects of these host plants on psyllid fecundity and longevity as well as mortality and developmental rate of psyllid nymphs. Host plants of both species used in this study were 30 cm in height grown in containers of potting media consisting of Canadian sphagnum peat, perlite and vermiculite mix. Plants were fertilized with 20-20-20 (N, P, K) soluble fertilizer every two weeks and watered three times per week. Plants were pruned two weeks prior to the initiation of experiments to obtain young flushes. Psyllids used in this study were from a colony reared in a