Effects of Acaricides on the Functional and Numerical Responses of the Phytoseid Predator Neoseiulus idaeus (Acari: Phytoseiidae) to Spider Mite Eggs

Integrated control tactics are often necessary for pest management. This is especially true for organisms such as the two-spotted spider mite, Tetranychus urticae Koch. The management of this mite pest species relies on pesticide use, but its short life cycle associated with high selection pressure results in frequent problems of acaricide resistance and population outbreaks. Therefore, combining acaricides and natural enemies is an appealing strategy for managing this pest species. The predatory mite Neoseiulus idaeus Denmark & Muma (Phytoseiidae) is important in arid environments, where other natural enemies show low efficacy. Thus, we investigated the effects of representative acaricides used for managing spider mites around the world in several crops (i.e., abamectin, fenpyroximate, and azadirachtin), on the functional and numerical responses of the phytoseid predator N. idaeus to increasing egg densities of its prey. Acaricide exposure did not affect the type of N. idaeus functional response or attack rate (a). However, acaricide exposure decreased the amount of consumed prey and increased prey handling time (Th). All acaricides affected the numerical response of the predator, which reduced oviposition rates. Therefore, caution is required in attempts to integrate the control methods.

Predatory phytoseiid mites associated with cassava in Kenya, identification key and molecular diagnosis (Acari: Phytoseiidae)

The objective of this study was to carry out a large survey in order to characterize Phytoseiidae species diversity on cassava in Kenya. A total of 29 species from 10 genera were identified in diverse ecological zones in Kenya. The warm-to-hot low midlands of eastern and the warm-humid coastal strip yielded over 70 % of the species identified. The dominant species were Euseius fustis (Pritchard and Baker) and Typhlodromalus aripo De Leon present in 37 and 34 % of samples, respectively. Typhlodromalus aripo was found persistent in coastal, eastern and western regions of Kenya while E. fustis was present in all sampled localities of the country. In addition to morphological diagnosis, molecular sequences for DNA fragments 12S, CytB, COI and ITS, were obtained for T. aripo and E. fustis. Molecular diagnosis has revealed the unexpected presence of Neoseiulus idaeus Denmark and Muma and indicated its misidentification as Neoseiulus onzoi (Zannou, Moraes and Oliveira) in a previous survey carried out in Kenya. Molecular sequences herein obtained will help further diagnosis of phytoseiid species and complement the international reference databases needed to assist molecular identification of Phytoseiidae species.

Feeding preference and predation rate of Neoseiulus idaeus(Acari: Phytotseiidae) feeding on different preys

Soybean (Glycine max (L.): Fabaceae) is considered the most important agricultural crop in Brazil. Phytophagous tetranychid mites such as Mononychellus planki McGregor, Tetranychus ludeni Zacher, and T. urticae Koch are considered pests of soybean crops. Neoseiulus idaeus Denmark & Muma (Phytoseiidae) is a predatory mite of T. ludeni and T. urticae. This study aimed at analyzing the feeding preference of N. idaeus among three types of prey (M. planki, T. ludeni, and T. urticae), its prey-stage preference, and its predation rate under controlled conditions. During immature stages of N. idaeus, we carried out observations to monitor predator survival and to ensure food availability (eggs and different prey stages) throughout the study period. Neoseiulus idaeus preferred T. urticae compared to T. ludeni and M. planki, and it preferred T. ludeni compared to M. planki. This predator preferred T. urticae and T. ludeni when compared to leaves without prey; however, when analyzed with M. planki and leaves without prey, it showed no preference. Regarding oviposition site, T. urticae was preferred over T. ludeni or M. planki. However, between T. ludeni and M. planki, N. idaeus preferred T. ludeni. This predator preferred to oviposit where T. urticae and T. ludeni were located instead of leaves without prey. However, when it was assessed with M. planki and on dry leaves without prey, there was no preferred oviposition site. These results show a strong preference for T. urticae as food; however, in the absence of this prey, N. idaeus feeds on T. ludeni and M. planki. In all immature stages and as adults, N. idaeus preferred T. urticae eggs. In protonymphal, deutonymphal, and adult stages it also consumed prey larvae and nymphs. Only adult N. idaeus consumed adult prey. The total predation rate for eggs, larvae, nymphs, and adults of T. urticae was 55.9%, 14.34%, 22.11%, and 7.65%, respectively. The average lifespan of females of this predator was 16.07 days, when they consumed 3.05 prey/female/day. These results suggest that N. idaeus has potential to be used in an applied biological control program for T. urticae.

Biological performance of the predatory mite Neoseiulus idaeus (Phytoseiidae): a candidate for the control of tetranychid mites in Brazilian soybean crops

The soybean (Glycine max (L.): Fabaceae) is considered the most important agricultural crop in Brazil. Phytophagous tetranychid mites as Mononychellus planki McGregor, Tetranychus ludeni Zacher and T. urticae Koch have been considered pest in soybean crops. Neoseiulus idaeus Denmark & Muma (Phytoseiidae) is a predatory mite of T. ludeni and T. urticae. The aim of the present study was to evaluate the biological performance of N. idaeus when fed on T. urticae, T. ludeni and M. planki, coming from the Northwest region of Rio Grande do Sul state, Brazil. The study was conducted in the laboratory with individual predators supplied with different preys. The mean duration (days) of N. idaeus egg-adult development was similar independently of supplied prey (T. ludeni - 5.29±0.03; M. planki - 5.34±0.05 and T. urticae - 5.23±0.03 days). Female viability was 90% when fed on M. planki and 100% when fed on T. ludeni and T. urticae. Mean fecundity of N. idaeus was lower when fed on M. planki (4.6±1.58 eggs/female) and higher when fed on T. ludeni (21.8±3.22) and T. urticae (26.2±2.41). The mean generation time (T) was lower when N. idaeus fed on M. planki than when fed on T. ludeni and T. urticae. The net reproductive rate (Ro) was 4.42±0.49 on M. planki, 17.77±0.55 on T. ludeni and 20.59±0.48 on T. urticae. The innate capacity for increase (rm) was lower when N. idaeus was fed on M. planki (0.09) and higher when such predator was fed on T. ludeni (0.20) and T. urticae (0.22 females/females/day). These results demonstrated that N. idaeus is able to reach the complete development feeding on all the three tetranychid species. Mononychellus planki demonstrated to provide a sub-optimal diet if compared to T. ludeni and T. urticae.