G. Andrew C. Beattie

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

Abstract 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.

Feeding behaviour of the Asiatic citrus psyllid, Diaphorina citri, on healthy and huanglongbing-infected citrus

Diaphorina citri Kuwayama (Hemiptera: Sternorrhyncha: Psyllidae) is a vector of huanglongbing, a disease of citrus that in Asia is caused by ‘Candidatus Liberibacter asiaticus’ (α‐Proteobacteria) (Las). Acquisition of Las by D. citri appears to be variable, and this variability may be due to the suitability of the host plants and their tissues for acquisition. Therefore, this study aimed to determine the effect of symptom severity of the disease on the feeding behaviour of D. citri. Use of an electrical penetration graph showed that the pathway phase of D. citri consisted of four waveforms, A, B, C, and D; waveforms A and B have not been reported for D. citri before. The remaining waveforms, E1, E2, and G, conform to those described before for D. citri. The duration of the non‐penetration period did not differ between healthy or infected plants. However, in moderately and severely symptomatic plants, the duration of the pathway phase increased, whereas the phloem phase was shorter. In all diseased plants, the times to first and sustained salivation in the phloem were longer than those in control plants, with the times being related to symptom severity. As symptom expression increased, the percentage of time spent by psyllids salivating during the phloem phase increased; however, the percentage of time spent in phloem activities reduced gradually from ca. 74% in the control plants to ca. 8% in the severely symptomatic plants. In contrast, the percentage of time spent on xylem activities increased, as did the proportion of psyllids feeding from xylem. The differences in the durations of the E waveforms on plants showing different levels of symptom expression may account for differences in acquisition found amongst studies; therefore, future work on the acquisition and transmission of Las needs to carefully document symptom expression.

Post-harvest disinfestation of lightbrown apple moth, Epiphyas postvittana Walker (Lepidoptera: Tortricidae), with an alkane

Lightbrown apple moth (LBAM), Epiphyas postvittana Walker was used as a test insect to evaluate a post-harvest oil, C15 Ampol CPD, and a spray oil, C23 Ampol DC-Tron NR, both applied as dips. CPD was much more efficacious than C23 DC-Tron NR against exposed third-instar larvae. Higher oil concentrations were required to penetrate and kill larvae sheltering under the calyx of oranges. LBAM eggs were more susceptible to CPD oil than larval stages. LBAM larvae dipped in sub-lethal doses of oil continued to develop, but the fecundity of both males and females was reduced. DC-Tron had a significant effect on egglaying. CPD and C23 DC-Tron NR affected the fertility of eggs laid. CPD oil sprayed at 50 ml litre−1 on adult LBAM moths reduced their fertility. Factors contributing to the higher efficacy of CPD and its potential use as a post-harvest treatment are discussed. © 1999 Society of Chemical Industry

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.

Conservation of natural enemy fauna in citrus canopies by horticultural mineral oil: comparison with effects of carbaryl and methidathion treatments for control of armored scales.

Abstract  The disruptive effects of an nC24 horticultural mineral oil (HMO) and two other insecticides (carbaryl and methidathion) on two armored scale insects and natural enemy fauna were evaluated in two citrus orchards. In the first orchard, all three spray treatments and non‐sprayed controls were distributed separately among individual trees in one block, whereas in the second orchard the control, HMO and methidathion treatments were applied at the level of whole blocks. The results in both orchards were similar. All three of the spray treatments had a lethal effect on the red scale insects and the effects of HMO and methidathion tested at the second site lasted for at least 19 weeks and for purple scale, at least 50 weeks. HMO did not have a significant effect on the abundance and species diversity of parasitoids and (for the most part) did not affect coccinellids and predatory mites. Both carbaryl and methidathion caused significant ongoing disruption to the above groups. No treatment resulted in the resurgence of the scale insects or the outbreak of phytophagous mites, even where whole blocks were sprayed.

Systematics and biology of two species of Microcera associated with armoured scales on citrus in Australia

Microcera coccophila has been regarded as an entomopathogen of armoured scales in Australia since the late 1800s. We confirmed its identity and presence in Australia using morphological and molecular data. We also confirmed that a related species, M. larvarum, is an entomopathogen of armoured scales in Australia. M. coccophila was recorded as a parasite of Aonidiella aurantii, A. citrina, Lepidosaphes beckii, L. gloverii and Unaspis citri in citrus orchards on the Central Coast of New South Wales. We recorded M. larvarum in these orchards in association with A. aurantii and one or more hosts that could not be identified due to their condition. The sexual and asexual morphs of both species are described. Genetic variation suggested that the taxa could represent various phylogenetic species. We fulfilled Koch’s postulates for both fungi in separate bioassays with Aspidiotus nerii. Infection was not dependent on the reproductive status of the scale. A laboratory study showed that Iridomyrmex rufoniger, a common ant in Australian citrus orchards, can passively disperse conidia of M. coccophila. Field observations suggested that the prevalence of the two fungal parasites in orchards is influenced by host scale densities, climate, and foraging by I. rufoniger workers on honeydew produced by their sternorrhynchan trophobionts, particularly Saissetia oleae. These foraging activities induced dense populations of A. aurantii by disrupting the activities of the scale’s natural arthropod enemies; this was followed by epizootics of M. coccophila that decimated populations of the scale.

The influence of sublethal deposits of agricultural mineral oil on the functional and numerical responses of Phytoseiulus persimilis (Acari: Phytoseiidae) to its prey, Tetranychus urticae (Acari: Tetranychidae)

Occasional pesticide application in integrated pest management to at least part of a crop requires that any biological control agents must re-invade previously sprayed areas in order that resurgent pests can be constrained. The ability of the phytoseiid predatory mite Phytoseiulus persimilis to feed on adult two-spotted spider mite (TSSM) Tetranychus urticae on excised leaf discs in both control conditions and in a treatment with a sub lethal residue of agricultural mineral oil (AMO) was assessed. The predator exhibited a Type II functional response with the asymptote significantly higher in the AMO conditions due to the fact that the prey grew slower and reached a smaller size in this treatment. In terms of prey volume eaten, the satiation level of the predator was unchanged by the AMO deposits. The numbers of eggs produced by adult P. persimilis females at densities of 4, 8 and 16 TSSM adult females/disc in the control were significantly higher than those in the AMO treatment, but were similar for the higher density levels, 32 and 64 prey per disc. Thus the functional response in terms of volume of prey eaten explained the numerical response in terms of predator eggs produced. The presence of AMO deposits when the prey were at high density had no effect on predator efficiency (volume eaten) but resulted in a lower intake than that in control conditions when there was a greater distance between prey.

Primary parasitoids of red scale (Aonidiella aurantii) in Australia and a review of their introductions from Asia.

We used morphological and molecular differences to confirm the identities of red scale (Aonidiella aurantii) and yellow scale (A. citrina), and their primary parasitoids, in Australia. An extension to the distribution of yellow scale was confirmed. Six primary parasitoids of red scale were identified: Aphytis chrysomphali, A. lingnanensis, A. melinus, Comperiella bifasciata, Encarsia citrina, and E. perniciosi. With the exception of A. lingnanensis, these parasitoids, and a species of Aphelinus, were detected in association with red scale during studies in citrus orchards in coastal New South Wales between 2009 and 2012. Two races of A. melinus were recorded: one from the Indian Subcontinent, the other previously only recorded in China. The studies, and reviews of historical records, led us to conclude that 4 parasitoids, A. lingnanensis, C. bifasciata, and both species of Encarsia, were present in Australia before successful or unsuccessful formal introductions between 1902 and 1970. The A. melinus race previously recorded in China may also have been present before the Indian Subcontinent race was formally introduced in 1961. We suggest the possibility that the natural distribution of some of the parasitoids may include East and Southeast Asia, and parts of Australasia. We found no reports of native armored scales being recorded on species and hybrids of Citrus introduced to Australia, and no reports of introduced armored scales being recorded on native Rutaceae, including 6 species of Citrus. However, we subsequently recorded yellow scale on Geijera parviflora, a native rutaceous tree.