Spatiotemporal association between the mite Brevipalpus yothersi and Citrus leprosis virus C in orange orchards.

Citrus leprosis virus C (CiLV-C) is an economically important pathogen and the main causative agent of leprosis disease in citrus orchards. The main vector of this disease, the mite Brevipalpus yothersi, is widely distributed in Mexican orchards on a wide range of citrus species. Despite the importance of both the virus and the mite, field studies recording their occurrence and co-occurrence are practically non-existent. We systematically sampled orange orchards for both CiLV-C and B. yothersi throughout the year. The distribution of the CiLV-C and B. yothersi was evaluated on each sampling occasion and their spatiotemporal associations were determined. Specifically, 100-112 orange trees, distributed in 18 rows (five or six trees per row), were sampled monthly between March 2017 and February 2018 (11 sampling dates). Twenty leaves per tree were sampled on each occasion. The number of mites per tree and the percentage of leaves per tree with disease symptoms were recorded. On each sampling occasion, spatiotemporal associations between mites and disease were determined using the Spatial Analysis by Distance Indices (SADIE) method. CiLV-C and B. yothersi were identified using molecular methods. Throughout the study, the distribution of CiLV-C was aggregated and the distribution of B. yothersi was random. No association was found between the virus and the mite on any of the sampling dates. In total, 173 mites were collected, but only 43 mites were found to be carrying CiLV-C. The reason for this lack of association between the virus and the mite, as well as the impact of our findings on the epidemiology of the disease in orange orchards, are discussed.

Variability in Damage Caused by the Mite Tetranychus urticae (Trombidiformes: Tetranychidae) Koch on Three Varieties of Strawberry.

The strawberry, Fragaria×ananassa Duchesne (Rosales: Rosaceae), is an important crop in Mexico. We evaluated the tolerance of three newly developed Mexican strawberry varieties (CP0615, CPLE-7, and CPJacona) to Tetranychus urticae Koch (Trombidiformes: Tetranychidae), the most important pest of strawberry. We evaluated the effect of three different initial mite densities on population growth, duration of each developmental stage and survival of T. urticae on the three strawberry varieties. We also compared the photosynthetic activity (Pn), sub-stomatal CO2 concentration (Ci), stomatal conductance (gs) and the area of leaf damaged in the three varieties. The largest final density of mites occurred on the variety CP0615, followed by the varieties CPLE-7 and CPJacona. There were no significant differences in the duration of T. urticae developmental stages amongst the varieties, except for larvae where the shortest duration was on variety CPLE-7. The proportion of eggs reaching the adult stage (survival) was significantly lower on the variety CPLE-7. The number and morphology of the trichomes did not play an important role in the outcomes, as they were similar in the three varieties. There were no significant differences in Pn, Ci, and gs values amongst the three varieties in the presence and absence of T. urticae. The area of leaf damaged in variety CPLE-7 was significantly smaller than for the other varieties. Based on these results, and with regard to spider mite tolerance, we believe that the variety CPLE-7 has the greatest potential for further development, and eventually, for use on a commercial scale in Mexico.

Metarhizium pingshaense applied as a seed treatment induces fungal infection in larvae of the white grub Anomala cincta.

Metarhizium pingshaense has potential as a control agent of the white grub Anomala cincta. We compared its ability to cause infection when applied as a seed treatment or directly to the compost around the plant roots. Although the greatest infection (93%) occured in the direct inoculation treatment, 50% of larvae still became infected by M. pingshaense applied as a seed treatment. The fungus persisted in the compost and also colonised the roots of the developing maize plants endophytically. More research is required but seed treatments with M. pingshaense have potential as cost-effective control options for A. cincta.

Diversity and Genetic Variation among Brevipalpus Populations from Brazil and Mexico.

Brevipalpus phoenicis s.l. is an economically important vector of the Citrus leprosis virus-C (CiLV-C), one of the most severe diseases attacking citrus orchards worldwide. Effective control strategies for this mite should be designed based on basic information including its population structure, and particularly the factors that influence its dynamics. We sampled sweet orange orchards extensively in eight locations in Brazil and 12 in Mexico. Population genetic structure and genetic variation between both countries, among locations and among sampling sites within locations were evaluated by analysing nucleotide sequence data from fragments of the mitochondrial cytochrome oxidase subunit I (COI). In both countries, B. yothersi was the most common species and was found in almost all locations. Individuals from B. papayensis were found in two locations in Brazil. Brevipalpus yothersi populations collected in Brazil were more genetically diverse (14 haplotypes) than Mexican populations (four haplotypes). Although geographical origin had a low but significant effect (ca. 25%) on the population structure, the greatest effect was from the within location comparison (37.02 %). Potential factors driving our results were discussed.

Contrasting effects of geographical separation on the genetic population structure of sympatric species of mites in avocado orchards.

Oligonychus punicae and Oligonychus perseae (Acari: Tetranychidae) are the most important mite species affecting avocado orchards in Mexico. Here we used nucleotide sequence data from segments of the nuclear ribosomal internal transcribed spacers (ITS1 and ITS2) and mitochondrial cytochrome oxidase subunit I (COI) genes to assess the phylogenetic relationships between both sympatric mite species and, using only ITS sequence data, examine genetic variation and population structure in both species, to test the hypothesis that, although both species co-occur, their genetic population structures are different in both Michoacan state (main producer) and Mexico state. Phylogenetic analysis showed a clear separation between both species using ITS and COI sequence information. Haplotype network analysis done on 24 samples of O. punicae revealed low genetic diversity with only three haplotypes found but a significant geographical population structure confirmed by analysis of molecular variance (AMOVA) and Kimura-2-parameter (K2P) analyses. In addition, a Mantel test revealed that geographical isolation was a factor responsible for the genetic differentiation. In contrast, analyses of 22 samples of O. perseae revealed high genetic diversity with 15 haplotypes found but no geographical structure confirmed by the AMOVA, K2P and Mantel test analyses. We have suggested that geographical separation is one of the most important factors driving genetic variation, but that it affected each species differently. The role of the ecology of these species on our results, and the importance of our findings in the development of monitoring and control strategies are discussed.

Species composition and abundance of Brevipalpus spp. on different citrus species in Mexican orchards.

We studied the abundance of Brevipalpus spp. in citrus orchards in the Mexican states of Yucatan, Quintana Roo and Campeche. Mites were collected from 100 trees containing a mixture of citrus species where sweet orange was always the main species. Eight collections were made at each location from February 2010 to February 2011. Mites from the genus Brevipalpus were separated from other mites surveyed and their abundance and relationships with the different citrus species were quantified throughout the collection period. A subsample of 25% of the total Brevipalpus mites collected were identified to species level and the interaction of mite species and citrus species were described. Brevipalpus spp. were present on all collection dates and their relative abundance was similar on all citrus species studies. The smallest number of mites collected was during the rainy season. Brevipalpus phoenicis (Geijskes) and Brevipalpus californicus (Banks) were the only two species present and they were found in all locations except Campeche, where only B. phoenicis was present. Yucatan and Campeche are at greater risk of leprosis virus transmission than Quintana Roo because the main vector, B. phoenicis, was more abundant than B. californicus. The implications of our results for the design of more accurate sampling and control methods for Brevipalpus spp. are discussed.