The whitefly species Bemisia tuberculata and Aleurotrixus aepim (Hemiptera: Aleyrodidae) are considered important cassava (Manihot esculenta) pests. Leaf color and other morphological characteristics can influence the pest’s interactions with the host plants. Thus, this study aimed to identify the relationship between whitefly occurrence and trichome density and leaf color in different cassava cultivars. The study was conducted in the field during the 2014/2015 and 2016/2017 crop seasons. The whitefly occurrence was surveyed in the cultivars, IAPAR 19, IPR Upira, IPR União, IAC 576-70, IAC 14, IAC 90, Catarina Branca, Santa Helena and Baianinha. The whitefly nymph quantification was correlated with non-glandular trichome density, luminosity (L*) and chroma (a* and b*) of the cassava leaves. IAPAR 19 and IAC 14 were less infested by whitefly nymphs when contrasted with IPR União, IPR Upira and Baianinha, which were the most infested. The lowest B. tuberculata infestations were correlated with lesser trichome density, highest light reflection and highest chroma in the sprout and the plant’s superior third portion leaves. Low A. aepim infestation in both crop seasons made it impossible to verify its correlation with the studied cassava plant characteristics. The cultivars IAPAR 19 and IAC 14 could contribute towards B. tuberculata management in regions with a history of whitefly infestation.
The green-belly stinkbug (Dichelops melacanthus) stands out due to its damage potential towards corn and wheat crops. The population distribution and size greatly influence the potential damage. The insect’s reproductive capacity depends on different temperature conditions during various crop seasons and its lifecycle. The study aimed to evaluate the influence of different constant temperatures on the D. melacanthus biology. The study was performed twice, once in the year of 2017, and again in 2019. The biological features were observed in temperature-controlled climate chambers with the following temperatures: 11, 16, 21, 26, 31 and 36 °C, each with a fluctuation of ±1 °C, using a RH of 65±15% and photophase of 14 h. The evaluations were conducted from eggs to adults in terms of: nymphal hatch period, each instar duration, female fecundity and egg viability. There were no eggs hatching at 11 ºC and it also reached 100% mortality during the second instar at 16 °C. The eggs-to-adult duration for the temperatures 21, 26, 31 and 36 °C in the trial of 2017 was 58.4, 30.1, 18.2 and 16.3 days, respectively. In the same temperatures, but during the 2019 trial, the eggs to adult duration was 58.1; 29.7; 21.3 and 19.1 days, respectively. The reproductive capacity in the temperatures of 21 and 36 °C impaired the female fecundity and egg viability. The temperatures 26 and 31 °C favored the development of D. melacanthus.
The objective of this study was to evaluate the infestation of Vatiga illudens in cassava varieties and to correlate its infestation with the physical and morphological parameters of resistance. The experiments were conducted in the 2014/2015 and 2016/2017 seasons, out in a randomized complete block design with nine treatments and five replicates. Nymphs and adults of V. illudens were evaluated on the abaxial surface of 16 leaves of the middle third of the plant. The density of trichomes was quantified with the use of electron micrographs, and the roughness of the epicuticular wax was assigned to the leaves of the shoot and the apical third. The color components L*, a*, b*, were measured with a portable digital colorimeter. The cultivars IAC 90 and Santa Helena demonstrated the smallest infestations in the 2014/2015 season and maintained low infestation in the 2016/2017 season. The varieties Baianinha, IAC 576-70 and Catarina-Branca, maintained high infestations in the both seasons. The density of trichomes of the middle third of the plants correlated negatively to the V. illudens infestation for the two seasons. The higher density on trichomes, negatively affects the infestation of V. illudens in cassava varieties, characterizing as a specific resistance factor to this species.
The loss caused by the shoot-fly (Neosilba perezi) was simulated through the elimination of the cassava`s terminal buds, with the objective to quantify this effect towards the roots productivity, flour production and propagative material production (stem cuts). The experimental design was random blocks, with three repetitions, in a factorial scheme with an additional treatment (10 × 4 + 1). Ten damage levels (10, 20, 30, 40, 50, 60, 70, 80, 90 and 100%) were studied, including a witness treatment (0%). The cassavas were treated during each of the four seasons of the year. The studied variables were: root productivity (t ha-1), flour production (t ha-1) and number of stem cuttings with a diameter greater than 20 and 25 mm. The induced damage in the cassava`s meristem did not significantly affect the root, nor the flour production. However, the stem cuttings production demonstrated a linear decrease in relation to the apical meristem damage level.
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