Distribution, biology, ecology and control of the psyllid Diaphorina citri Kuwayama, a major pest of citrus : a status report for China

The Asiatic citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is a major pest of citrus in China. Its status derives, not from the damage it causes, but from its role as the only known vector in China of huanglongbing, a phloem-limited bacterial disease of international importance. The disease can devastate orchards within a few years of planting. It also poses a major threat to endangered indigenous citrus germplasm in Asia and Australasia. The distribution, biology, ecology and control of the psyllid in China are reviewed in these contexts. Constraints and challenges related to control of the vector in China are discussed

Influences of leaf age and type, non-host volatiles, and mineral oil deposits on the incidence, distribution, and form of stylet tracks of Diaphorina citri

Psyllids produce saliva that gels to form a protective sheath around their stylets. This saliva can be visualized as stylet tracks, and we have used the presence of tracks to study the feeding behaviour of Diaphorina citri Kuwayama (Hemiptera: Liviidae). Both single and branched tracks were produced by nymphs and adults, and the tracks made by males and females did not differ. Tracks dissipated from calamondin leaves within a 7-day post-feeding period after adults fed for 2 days and numbers of tracks declined with increasing maturity of calamondin leaves. In the six host plants studied, most psyllids fed abaxially from midribs and most probes traversed or terminated in the tissue (midrib, lateral vein, minor vein, or mesophyll) above which the stylets entered the leaf or leaflet. The number of tracks and landings were recorded on the six hosts in choice tests. More tracks were found in leaves or leaflets of orange jasmine, wampee, and trifoliate orange than in sour orange, calamondin, and lemon. Orange jasmine is considered a preferred host of D. citri, and this is in agreement with the number of tracks found in this study, but not the number of landings. Trifoliate orange is considered a poor host of D. citri, which, in this study, is reflected in the low number of landings, but not in the numbers of tracks. Our results indicate that the presence of adult psyllids on a plant may not reflect its host status, and that the presence of stylet tracks should also be determined in host preference studies. When calamondin leaves were paired with leaves of guava, billygoat weed, or greenleaf desmodium, the presence of volatiles from these plants reduced feeding by adults on calamondin and suggests that understoreys of billygoat weed or desmodium in orchards may also reduce feeding. A negative, exponential relationship between numbers of tracks per leaf and the concentrations of an agricultural mineral oil applied to leaf surfaces was found. This reduction in feeding, in conjunction with reductions in oviposition, has practical implications for suppressing psyllid populations in orchards

Phytotoxicity of narrow-range petroleum spray oils to satsuma mandarin, Citrus reticulata Blanco

The phytotoxicity of narrow-range petroleum spray oils, D-C Tron produced by Caltex, to satsuma mandarin was investigated at Huangyan, Zhejiang, China, in 1998-2000. D-C Tron at 0.5% was sprayed 4-10 times every year from late April to early October. Spray operations were conducted after 16.00 h during midsummer. Bad effects were not found on leaf drop, fruit drop, fruit yield and quality, except that monstrous flower rate was increased when spray was performed during flower bud period and sunburn disease spot appeared slightly more visible when sprayed in September and October. Cumulation dosage per year should be controlled below 4%