Life Table Parameters of Tetranychus merganser Boudreaux (Acari: Tetranychidae) on Five Host Plants.

The quality of the host plant affects the life history parameters of tetranychid mites. The biology and fertility life tables of Tetranychus merganser on five host plants (Carica papaya, Phaseolus vulgaris, Capsicum annuum var. glabriusculum, Helietta parvifolia, and Rosa hybrida) were assessed under laboratory conditions at 28 ± 1 °C and 70-80% relative humidity (RH) with a photoperiod of 12:12 h (L:D). The development period of immature females differed among the tested host plants and ranged from 9.32 days on P. vulgaris to 11.34 days on H. parvifolia. For immature males, it ranged from 9.25 days on P. vulgaris to 11.50 days on H. parvifolia. The female survival rate varied from 53.97% on H. parvifolia to 94.74% on P. vulgaris. The highest total fecundity rate was recorded on P. vulgaris (125.40 eggs/female) and the lowest on H. parvifolia (43.92 eggs/female). The intrinsic rate of increase (rm) varied from 0.271 (H. parvifolia) to 0.391 (P. vulgaris). The net reproductive rate (RO) was higher on P. vulgaris than on the other host plants. The longest mean generation time (GT) was calculated on C. annuum var. glabriusculum and the shortest on Rosa hybrida. The demographic parameters suggest the unsuitability of H. parvifolia as the host for the development of red spider mites, and the best performance of T. merganser was on P. vulgaris.

Evaluation of Resistance of Eleven Maize Races (Zea mays L.) to the Red Spider Mite (Tetranychus merganser, Boudreaux).

At least 59 maize races (Zea mays L.) have been registered in Mexico. The feeding damage caused by insects and mites to maize crops generates up to ~30% of maize yield losses. Spider-mite-resistant plants are needed. The red spider mite, Tetranychus merganser Boudreaux (Acari: Tetranychidae), is distributed in the United States, China, Mexico, and Thailand. It is considered a potential pest in Mexican agriculture. The aim of this study was to evaluate the resistance mechanisms (antixenosis and antibiosis) of 11 native maize populations, representative of each race of maize grown in Tamaulipas, Mexico, to T. merganser under laboratory conditions. The aim was also to obtain information on the chemical composition and some morphological characteristics of these maize races and to identify resistant maize races for incorporation into a breeding program. Antixenosis was assessed by non-preference for oviposition and feeding. Antibiosis was measured by growth rate (ri). The presence of secondary metabolites in the 11 maize races were different. In the 11 maize races, quantitative analysis of total phenol concentration, total flavonoid concentration, and antioxidant capacity were significantly different. The multivariate analysis of variance showed that there is evidence of antixenosis noted by maize race differences in egg laying and percentage feeding damage but not of antibiosis noted by growth rate. Red spider mites laid significantly more eggs on the Celaya (24 h: 25.67 ± 17.04, 48 h: 42.67 ± 26.86, 72 h: 49.33 ± 28.54) race than on Raton (24 h: 7.00 ± 5.00, 48 h: 12.67 ± 8.02, 72 h: 14.67 ± 9.29) and Elotes Occidentales × Tuxpeño (24 h: 9.67 ± 5.85, 48 h: 15.33 ± 10.69, 72 h: 17.67 ± 10.97) races. However, the growth rate and mortality of T. merganser in the 11 corn races were similar. The Vandeño (24 h: 11.67 ± 2.89, 48 h: 27.67 ± 7.64, 72 h: 30.00 ± 18.03) and Tabloncillo × Tuxpeño (24 h: 18.33 ± 7.64, 48 h: 25.00 ± 8.66, 72 h: 25.00 ± 8.66) races were the most resistant to red spider mite damage, whereas the most susceptible race was Celaya (24 h: 26.67 ± 15.28, 48 h: 48.33 ± 29.30, 72 h: 65.00 ± 30.00). Further analysis by PCA at 24, 48, and 72 h found the Celaya race positively correlated to growth rate and oviposition of T. merganser and to a lesser extent with the percentage of feeding damage, suggesting that the Celaya race was most susceptible to T. merganser. At 24 h, the Vandeño race was most resistant, given a negative correlation to growth rate and oviposition by T. merganser. The PCA at 48 and 72 h noted the Elotes Occidentales × Tuxpeño race was most resistant to red spider mite, with negative relationships to growth rate and oviposition and, to a lesser extent, to feeding damage. This resistance is due to the differences in both its morphological characteristics and the secondary metabolites present in their leaves.

The Resistance of Seven Host Plants to Tetranychus merganser Boudreaux (Acari: Tetranychidae).

Red spider mites, Tetranychus merganser Boudreaux (Acari: Tetranychidae), is an agricultural pest that causes economic losses in papaya and nopal crops in Mexico. The aim of this research was to assess antibiosis and antixenosis as resistance mechanisms in seven host plants (Thevetia ahouai, Carica papaya, Phaseolus vulgaris, Moringa oleifera, Pittosporum tobira, Helietta parvifolia, Capsicum annuum var. glabriusculum) to red spider mites. Antixenosis was evaluated by non-preference for oviposition and feeding, antibiosis by infinitesimal rate of increase, finite rate of increase and doubling time, and the percentage of spider mites mortality. Oviposition and damage by feeding of T. merganser were significantly greater on C. papaya than on the other host plants. The growth rate of the spider mite was significantly lower in P. tobira and T. ahouai than in the other host plants. The percentage of hatched eggs of T. merganser was significantly higher in P. vulgaris than in the other plant species. Based on the demographic parameters, survival, food intake, and oviposition, these results indicated that compared with C. papaya, P. tobira and T. ahouai were more resistant. These results may be due to the fact that they were plants species of different families. The resistant plants can be studied as alternatives in the management of T. merganser.

Social and environmental factors in the diversity of tomato landraces from the South-Central region of Mexico / Influência de fatores sociais e ambientais na diversidade de variedades crioulas de tomateiro da região Centro-Sul do México

ABSTRACT: In the present study, we investigated the influence of social and environmental factors in the genetic diversity of tomato landraces in the South-Central region of Mexico. A total of 30 tomato landraces, collected in 18 villages with different ethnolinguistic affiliations, were analyzed. We reported that the genetic diversity of tomato landraces is associated with the ethnolinguistic group, weather, and soil-type present in the region studied. Our results showed that there are morphological differences between landraces grown by different ethnolinguistic groups; however, there was also evidence of morphological similarities between landraces from groups with different ethnolinguistic affiliations. Finally, different selection criteria, mainly fruit color, size and shape, plays an important role in the phenotypic divergence among landraces grown in different traditional farming systems.

RESUMO: No presente estudo investigamos a relação da afiliação etnolinguística com a diversidade genética de variedades locais de tomate na região Centro-Sul do México. Um total de 30 variedades de tomate, coletadas em 18 aldeias com diferentes afiliações etnolinguísticas, foram analisadas. Verificamos que a diversidade genética das variedades crioulas de tomate está associada ao grupo etnolinguístico presente na região estudada. Nossos resultados mostram que existem diferenças morfológicas entre raças cultivadas por diferentes grupos etnolinguísticos. No entanto, também houve evidências de semelhanças morfológicas entre raças de grupos com diferentes afiliações etnolinguísticas. Finalmente, diferentes critérios de seleção, como, principalmente, cor, tamanho e forma dos frutos, desempenham um papel importante na divergência fenotípica entre as variedades crioulas cultivadas em diferentes sistemas agrícolas tradicionais.