Neoseiulus baraki (Acari: Phytoseiidae) survival and walking in response to environmental stress

Living organism is exposed to the influence of various environmental conditions. These environmental conditions can trigger stress and compromise the fitness of the organism. As living organisms, phytoseiid mites are frequently exposed to a range of environmental stressors. In the present study, we attempted to explore the responses of the Neoseiulus baraki to environmental stress factors (temperature and humidity). Initially, the effect of different temperature (18–33 °C) and relative humidity (10–95%) levels on the survivorship of unfed N. baraki females was evaluated. Next, we estimated the walking parameters (distance traveled and average walking speed) with a computerized tracking system and we tested how N. baraki is constrained in their effective displacement by their ability to walk and survive in absence of food. The proportion of surviving N. baraki as well as mean survival time decreased significantly with increasing temperature. The opposite trend was observed to relative humidity. The distance covered by N. baraki reduced with increasing temperature (when only taking the temperature dependence of the survival time but not of walking speed and neither the tortuosity of the walking path) ranged from 550 m at 18 ºC to 100 m at 33 ºC. Under climatic conditions representative for the Tropics (27 ºC and 75 % RH) N. baraki was able to survive up to 1.5 days (36 h) without feeding and covered 0.9 m in 10 min as displacement estimated by walking.

Predator performance is impaired by the presence of a second prey species

The simultaneous infestation of a plant by several species of herbivores may affect the attractiveness of plants to the natural enemies of one of the herbivores. We studied the effect of coconut fruits infested by the pestsAceria guerreronisandSteneotarsonemus concavuscutum, which are generally found together under the coconut perianth. The predatory miteNeoseiulus barakiproduced lower numbers of offspring on fruits infested withS. concavuscutumand on fruits infested with both prey than on fruits withA. guerreronisonly. The predators were attracted by odours emanating from coconuts withA. guerreronis, but not by odours from coconuts withS. concavuscutum, even whenA. guerreroniswere present on the same fruit. FewerN. barakiwere recaptured on fruits with both prey or withS. concavuscutumthan on fruits with onlyA. guerreronis. Furthermore, the quality ofA. guerreronisfrom singly and multiply infested coconuts as food forN. barakidid not differ. Concluding, our results suggest thatN. barakidoes not perform well whenS. concavuscutumis present on the coconuts, and the control ofA. guerreronisbyN. barakimay be negatively affected by the presence ofS. concavuscutum.