Molecular differentiation of the Murraya paniculata Complex (Rutaceae: Aurantioideae: Aurantieae).

BACKGROUND: Orange jasmine has a complex nomenclatural history and is now known as Murraya paniculata (L.) Jack. Our interest in this common ornamental stemmed from the need to resolve its identity and the identities of closely related taxa as hosts of the pathogen 'Candidatus Liberibacter asiaticus' and its vector Diaphorina citri. Understanding these microbe-vector-plant relationships has been hampered by taxonomic confusion surrounding Murraya at both the generic and specific levels. RESULTS: To resolve the taxonomic uncertainty, six regions of the maternally-inherited chloroplastal genome and part of the nuclear-encoded ITS region were amplified from 85 accessions of Murraya and Merrillia using the polymerase chain reaction (PCR). Clustering used maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI). Chronograms were produced for molecular dating, and to test the monophyly of Murraya rigorously, using selected accessions of Murraya and 26 accessions of the Rutaceae and Simarubaceae. Sequence data from the ITS and chloroplastal regions suggest that Murraya paniculata (sensu (Swingle WT and Reece CR, The Citrus Industry, p. 190-430, 1967)) can be separated into four distinct but morphologically somewhat cryptic taxa: Murraya paniculata (sensu (Mabberley DJ, Taxon 65:366-371, 2016)), M. elongata, M. sumatrana and M. lucida. In addition, Murraya omphalocarpa was identified as a putative hybrid of M. paniculata and M. lucida with two geographically isolated nothovarieties representing reciprocal crosses. Murraya is monophyletic, and molecular dating suggests that it diverged from Merrillia during the Miocene (23-5 Ma) with this Murraya group speciating and dispersing during the Middle Miocene onwards. CONCLUSIONS: The accessions from Asia and Australasia used in this study grouped into biogeographical regions that match herbarium specimen records for the taxa that suggest natural allopatric distributions with limited overlap and hybridity. Murraya paniculata has been distributed around the world as an ornamental plant. The division of the Murraya paniculata complex into four species with a rare hybrid also confirms morphological studies.

Host and environmental factors influencing 'Candidatus Liberibacter asiaticus' acquisition in Diaphorina citri.

BACKGROUND: Diaphorina citri is a vector of 'Candidatus Liberibacter asiaticus' (CLas) associated with citrus Huanglongbing. In this study, the infection and titers of CLas in the psyllid, were monitored for life cycle stage, sex, host-plant CLas titer, host-plant genotype, and ambient temperature. RESULTS: Acquisition efficiency of CLas by D. citri was highest in nymphs reared at 25 °C on a host plant with high CLas titers but was independent of the host genotypes assessed and of vector sex. We further observed that D. citri nymphs acquired CLas more rapidly than adults based on acquisition access periods (AAPs). CLas did not multiply in the alimentary canal, hemolymph, and salivary glands of adults for 18 days after a 3-day AAP as adult. However, CLas multiplication was detected in hemolymph and salivary gland of adults after the bacterium was acquired by nymphs. Eighty percent of salivary glands of adults contained CLas 18 days after a 3-day AAP as nymph compared to 10% 18 days after a 3-day AAP as adults. CONCLUSION: Different factors tested herein influenced CLas acquisition efficiency of D. citri, CLas multiplication and spread inside the psyllid. These observations serve to better understand mechanisms of CLas infection in D. citri. © 2018 Society of Chemical Industry.

Population diversity of Diaphorina citri (Hemiptera: Liviidae) in China based on whole mitochondrial genome sequences.

BACKGROUND: Diaphorina citri (Asian citrus psyllid; ACP) transmits 'Candidatus Liberibacter asiaticus' associated with citrus Huanglongbing (HLB). ACP has been reported in 11 provinces/regions in China, yet its population diversity remains unclear. In this study, we evaluated ACP population diversity in China using representative whole mitochondrial genome (mitogenome) sequences. Additional mitogenome sequences outside China were also acquired and evaluated. RESULTS: The sizes of the 27 ACP mitogenome sequences ranged from 14 986 to 15 030 bp. Along with three previously published mitogenome sequences, the 30 sequences formed three major mitochondrial groups (MGs): MG1, present in southwestern China and occurring at elevations above 1000 m; MG2, present in southeastern China and Southeast Asia (Cambodia, Indonesia, Malaysia, and Vietnam) and occurring at elevations below 180 m; and MG3, present in the USA and Pakistan. Single nucleotide polymorphisms in five genes (cox2, atp8, nad3, nad1 and rrnL) contributed mostly in the ACP diversity. Among these genes, rrnL had the most variation. CONCLUSION: Mitogenome sequences analyses revealed two major phylogenetic groups of ACP present in China as well as a possible unique group present currently in Pakistan and the USA. The information could have significant implications for current ACP control and HLB management. © 2018 Society of Chemical Industry.

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.

Genetic variation amongst biotypes of Dactylopius tomentosus.

The tomentose cochineal scale insect, Dactylopius tomentosus (Lamarck) (Hemiptera: Dactylopiidae), is an important biological control agent against invasive species of Cylindropuntia (Caryophyllales: Cactaceae). Recent studies have demonstrated that this scale is composed of host-affiliated biotypes with differential host specificity and fitness on particular host species. We investigated genetic variation and phylogenetic relationships among D. tomentosus biotypes and provenances to examine the possibility that genetic diversity may be related to their host-use pattern, and whether their phylogenetic relationships would give insights into taxonomic relatedness of their host plants. Nucleotide sequence comparison was accomplished using sequences of the mitochondrial cytochrome c oxidase I (COI) gene. Sequences of individuals from the same host plant within a region were identical and characterized by a unique haplotype. Individuals belonging to the same biotype but from different regions had similar haplotypes. However, haplotypes were not shared between different biotypes. Phylogenetic analysis grouped the monophyletic D. tomentosus into 3 well-resolved clades of biotypes. The phylogenetic relationships and clustering of biotypes corresponded with known taxonomic relatedness of their hosts. Two biotypes, Fulgida and Mamillata, tested positive for Wolbachia (α-Proteobacteria), a common endosymbiont of insects. The Wolbachia sequences were serendipitously detected by using insect-specific COI DNA barcoding primers and are most similar to Wolbachia Supergroup F strains. This study is the first molecular characterization of cochineal biotypes that, together with Wolbachia sequences, contribute to the better identification of the biotypes of cochineal insects and to the biological control of cacti using host-specific biotypes 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.

Development of Epiphyas postvittana (Lepidoptera: Tortricidae) on leaves and fruit of orange trees.

Development of Epipyas postvittna (Walker) (Lepidoptera: Tortricidae), on leaves and fruit of 'Valencia', 'Washington navel', and 'Navelina' orange trees was studied under constant and fluctuating temperatures. E. postvittna was able to complete its life cycle feeding exclusively on leaves or fruit of orange trees. However, larval survival rate was very low (< 20%) on orange tissues compared with that on noncitrus hosts. Among the four types of orange tissues, young orange leaves and fruit afforded larvae higher survival rates than mature orange leaves and fruit. Fruit (young or mature) produced heavier pupae than leaves (young or mature). Larvae developed more slowly on mature orange fruit than on other orange materials and more slowly on orange leaves than on leaves of most noncitrus hosts. Degree-day accumulations based on the fastest developmental rates obtained in this study suggested that E. postvittna is capable of completing 4.4-4.7 generations per year in orange orchards in the Riverina region of New South Wales, Australia. Implications of the results in the management of the insect in citrus are discussed.

Evaluation of mating disruption for control of lightbrown apple moth (Lepidoptera: Tortricidae) in citrus.

Three large-scale mating disruption (MD) trials were conducted from 2001 to 2004 in an organic citrus orchard in inland southeastern Australia to evaluate the effectiveness of the MD dispenser Isomate LBAM Plus in controlling lightbrown apple moth, Epiphyas postvittana (Walker), in citrus. At the application rate of 364-728 dispensers per ha, the dispensers reduced pheromone trapping of E. postvittana to almost undetectable levels for approximately 6 mo in the treated area. During this period, most sentinel females in the treated area failed to mate. Infestation by E. postvittana in the treated area was reduced by >50%. If distributed in citrus orchards in late winter (August), the dispensers can be expected to remain effective until next February in southeastern Australia, covering the period when most fruit scarring caused by its larvae occurs.