Ángel Rebollar-Alviter

Insecticide resistance of adults and nymphs of Asian citrus psyllid populations from Apatzingán Valley, Mexico

BACKGROUND Control of the Asian citrus psyllid Diaphorina citri Kuwayama, the most important pest of citrus worldwide, is based on the use of insecticides, though unsatisfactory results have recently been reported. In this study, insecticide resistance of D. citri to three insecticides (bifenthrin, malathion, and chlorpyrifos) was examined. RESULTS Three populations (designated Dci-CParácuaro, Dci-El Junco, and Dci-Antúnez) of both adults and fourth-instar D. citri individuals were collected in 2014 at two different times and on one occasion, respectively, from three locations (Crucero de Parácuaro, El Junco, and Antúnez). These locations represent the major commercial Mexican lemon production areas in the Apatzingán Valley in the state of Michoacán, Mexico. The three populations of D. citri adults and fourth-instar nymphs at the different collection times showed low levels of resistance (≤7-fold) to bifenthrin, but were very resistant to malathion (≤345- and ≤432-fold for adults and fourth instars, respectively) and chlorpyrifos (≤2435- and ≤1424-fold for adults and fourth instars, respectively). CONCLUSION Resistance levels to the tested insecticides were highly variable but homogeneous among seasons and localities. Resistance management programmes that include crop sanitation, use of biological and cultural control practices, and rotation of insecticide classes should be established, particularly in areas where D. citri has developed resistance to malathion and chlorpyrifos.

Identification, Parasitoids, and Population Dynamics of a Blackberry Leafroller (Lepidoptera: Tortricidae) from Michoacán, Mexico

Abstract. The blackberry, Rubus sp., crop in the state of Michoacán, Mexico is the second-most important crop after avocado, Persea americana Mill., in relation to value of production and employment. In this study was identified a blackberry leafroller, its parasitoids, and population dynamics in two commercial orchards at Michoacán, Mexico, during the growing seasons of 2007 and 2008. Collected rolled leaves containing larvae and pupae where maintained in a laboratory until leafroller adults and their parasitoids emerged. Population dynamics of moths were determined using wing traps containing the sex pheromone of Argyrotaenia citrana (Fernald) (Lepidoptera: Tortricidae). Numbers of males caught peaked in September and November 2007 at the two locations. After these months, numbers gradually decreased to almost zero during the dry season in 2008. Moths that emerged were identified as Argyrotaenia montezumae (Walsingham) (Lepidoptera: Tortricidae). Of the A. montezumae larvae collected in the field, 38% were parasitized by Apanteles near aristoteliea Viereck (Hymenoptera: Braconidae), 9% by Colpoclypeus michoacanensis Sánchez and Figueroa (Hymenoptera: Eulophidae), and 3% by unidentified specimens of the family Ichneumonidae. Males of A. montezumae were attracted to the sex pheromone of A. citrana. The greatest number of moths trapped during the growing season coincided with the periods of intense vegetative growth and harvest.

Population Fluctuation and Spatial Distribution of Trioza aguacate (Hemiptera: Triozidae) on Avocado (Lauraceae) in Michoacan, Mexico

Abstract The psyllid Trioza aguacate Hollis & Martin (Hemiptera: Triozidae) causes deformation of leaves and young shoots of avocado. In recent years, population densities of this pest in avocado orchards have increased. The objectives of this study were to determine seasonal fluctuations of the populations of eggs, nymphs, and adults of T. aguacate, how these fluctuations are related to the incidence of avocado vegetative shoots, temperature and rainfall at 3 different altitudes in Michoacan, Mexico, i.e., 2,130 m, 1,860 m and 1,293 m. In addition, we attempted to determine the spatial distributions of nymphs and adults found on avocado vegetative shoots. We sampled the populations of adult and immature T. aguacate every 20 days from Jan 2012 to Jul 2013. To estimate population densities, 9 trees were selected in each orchard, and the trees were distributed in the form of a cross. From each replicate of trees, 4 shoots were randomly collected, and the eggs and nymphs were counted on them. Adults counts were obtained from yellow traps established at the 4 cardinal points in each tree. During the same period, young vegetative shoots, temperature and rainfall were recorded. The results showed that this psyllid was not present at all in the orchard located at the low altitude level of 1,293 m. The psyllid was present at the medium altitude site from Jan to Jun, and from Dec to Jun at the high altitude site. All of the development stages were most abundant from Mar to May, when avocado vegetative shoots were most abundant in both years. The abundance of eggs and nymphs showed a positive relationship with young vegetative shoots, a negative relationship with rainfall, and the eggs showed a positive relationship with temperature. The incidence of adults was strongly related with spring budding, but not significantly correlated with temperature. Both nymphs and adults had an aggregated spatial distribution.

Phylogenetics and histology provide insight into damping-off infections of ‘Poblano’ pepper seedlings caused by Fusarium wilt in greenhouses

The ‘Poblano’ pepper crop is economically important in Mexico and throughout the world as it is used as a hot spice in food. The cultivated area of the ‘Poblano’ pepper crop is decreasing yearly for many reasons, among them a wilt disease commonly associated with Fusarium spp. This disease is a problem of field and greenhouse production plants. Moreover, it is not clear whether the pathogens that cause wilt in mature plants are the same as those involved in the damping-off symptoms and death of pepper seedlings in greenhouses. For this reason, the aim of the present study was to identify the causal agent of damping-off in pepper during seedling production, establish its relationship with the causal agent of wilting in mature plants, and determine whether histological damage in seedlings occurs. Isolates were recovered from the crown rot and stem base of 4-month-old infected ‘Poblano’ mature pepper plants and were identified using morphological and phylogenetic approaches. Fusarium oxysporum and F. solani were isolated from the crown rot and base stem, respectively. A pathogenicity test showed that both species caused damping-off in pepper seedlings. Histological studies with inoculated seedlings of both isolates showed several changes in the external cortex, epidermal cells, endodermis, Casparian strips, cell size, and xylem wall. Casparian strip rupture resulted in permeability loss and regulatory activity to maintain the cellular equilibrium inside the vascular bundles. Hence, according to these findings, producers should avoid seedling contamination by infected mature plants because the aggressiveness of Fusarium isolates can cause rapid seedling mortality.

Potential Distribution of Drosophila suzukii (Diptera: Drosophilidae) in Relation to Alternate Hosts in Mexico

Abstract The spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is one of the most important pests of berry crop production in Mexico. The purpose of this research was to model the potential distribution of D. suzukii in the Mexico relative to 4 non-crop hosts using Maximum Entropy Ecological Niche Modeling. Spotted wing drosophila records were collected from a survey conducted in commercial blackberry plots and non-cultivated areas between 2013–2015. The data for the presence of non-crop hosts in the country and the bioclimatic variables used in the modeling were obtained from the Global Biodiversity Information Facility and WorldClim websites, respectively. For climatic variable selection, a principal component analysis on climatic variables was conducted prior to the MaxEnt modeling. The results demonstrate that the potential distribution of spotted wing drosophila was primarily in central Mexico. However, other suitable locations in the southeastern portion of the county were identified, which were not previously known. Likewise, the joint modeling depicted areas of coincidence between the spotted wing drosophila distribution and 4 alternating non-crop hosts commonly distributed in the berry-producing region, which includes the states of Michoacán, Jalisco, Guanajuato, and Mexico. This joint modeling of the potential distribution of spotted wing drosophila and non-crop hosts partly explains how the populations of the pest sustain themselves during seasons of low or no commercial berry production in Mexico.