Suitability of ‘Cleopatra’ Mandarin as a Host Plant for Diaphorina citri (Hemiptera: Psyllidae)

The Asian citrus psyllid, Diaphorina citri (Ku wayama) is currently the most significant insect pest of Florida citrus as the vector of Candidatus Liberibacter asiaticus, the phloem-limited bacte rium associated with citrus greening disease, also known as huanglongbing (HLB). The biology of D. citri has been studied by Catling (1970); Pande (1971); Capoor et al. (1974); Yang (1989); Liu & Tsai (2000); Nakata (2006); and Nava et al. (2007). In these studies, the host range of D. citri is reported to comprise numerous species within the Rutaceae, including citrus and close citrus relatives. While there are many field observations regarding host-plant associations of D. citri (Hal bert & Manjunath 2004), there are only 2 labora tory studies (Tsai & Liu 2000; Nava et al. 2007) in which factors including fecundity, adult longevity, sex ratio, and survival and development period of immature stages have been compared on differ ent host plants. In both studies, significant differ ences were reported for adult fecundity and sur vival of nymphs when D. citri was reared on dif ferent host plants. However, despite these differ ences, all citrus species evaluated were considered to be suitable host plants for D. citri. During the course of our studies on the biology of D. citri, we observed a lack of successful devel opment from egg to adult by D. citri on 'Cleopatra' mandarin (Citrus reshni Hort, ex Tan.) growing in both the field and greenhouse. Based on these ob servations, we compared the suitability of 'Cleo patra' mandarin versus 'sour orange' (Citrus au rantium) as host plants for D. citri by assessing oviposition rate, survival, and developmental pe riod on each host. Adult D. citri used in experiments were ob tained from a colony reared on Murraya koenigii in a greenhouse at the Citrus Research and Edu cation Center, Lake Alfred, Florida. Colony plants were maintained in polyester/nylon netting cages (61x61x91.5 cm3) (Bioquip, Rancho Dom?nguez, CA). Test plants of'Cleopatra' mandarin and 'sour orange' (30-50 cm in height) were grown from seed in the greenhouse, pruned, and fertilized prior to use in experiments to ensure new leaf growth for psyllid oviposition. Clear acetate cylin ders (34 cm height 6 cm diameter) were used to cage adult psyllids on new leaf growth. One end of each cylinder was covered with extra fine muslin and the opposite end, in which the plant was in serted, was sealed with a sponge to prevent psyl lids from escaping. To ensure proper ventilation, a small opening (5x5 cm) covered with extra fine muslin was made in the side of each cage, 5 cm from the top of the cage. All experiments were conducted under greenhouse conditions with an average temperature of 28.8 ? 6.79?C and 70.9 ? 27.31% relative humidity. Oviposition rate was assessed over a period of 15 d by caging 1 female D. citri on new leaf growth of 10 'Cleopatra' mandarin and 'sour orange' seed lings. Two male D. citri were confined with each female to allow multiple matings, which has been demonstrated to maximize reproductive output (Wenninger & Hall 2008). Female psyllids were moved every 3 d to new plants to provide suitable oviposition sites. Eggs laid on each plant were counted and remained caged until adult emer gence. Survival from egg to adult was calculated as the number of the adults emerged divided by the number of eggs laid per plant. Sex ratio of the emerged adults was determined. To compare the duration of the egg stage and each of the instars between the 2 host plants, fe male adult psyllids from the greenhouse colony were caged on new leaf growth of both citrus spe cies under greenhouse conditions as described above. After oviposition, the adults were removed from the cages and eggs were counted with use of a stereomicroscope. The eggs were checked daily and when a first instar emerged, it was trans ferred with a fine paintbrush and caged on young leaf tissue of a seedling of the same species. Nymphs were checked daily for ecdysis until they reached the adult stage to determine develop mental rate for each instar. All data collected were analyzed and compared by 2-sample f-test statistics (Analytical Software 2008). During the 15-d caging period, significantly fewer eggs were laid on "Cleopatra' mandarin compared to 'sour orange' (2-sample ?-test, t = 6.34, df = 58, < 0.0001). The mean number of eggs laid by female D. citri was 24.1 ? 2.7 and 80.2 ? 8.5 on 'Cleopatra' mandarin and 'sour orange,' respectively. Survival to the adult stage on 'Cleo patra' mandarin was 4.38 ? 1.46%, and signifi cantly lower compared to survival on 'sour orange' (62.21 ? 2.86%) (t = 18.03, df= 58, < 0.0001). Survival on 'sour orange' was lower compared to results reported in Tsai & Liu (2000), who found a survival rate of 71% on 'sour orange'. Differences may be due to slight differences in environmental conditions under which experiments were con ducted. Host plant did not have any effect on the sex ratio (0.50 ? 0.04 on sour orange, 0.50 ? 0.09 on Cleopatra) (t = 0.16, df= 35, = 0.8766). The development rate of psyllid nymphs was significantly longer for 'Cleopatra' mandarin com