Influence of relative humidity on the growth and development of the Mite Typhlomalus aripo De Leon (Acari: Phytoseiidae): Evidence from Laboratory and Greenhouse experiments

Abstract

The influence of selected relative humidity regimes on the development and growth of the various immature stages from egg to adult of the predacious mite Typhlodromakus aripo de Leon was studied in the laboratory at a constant temperature of 27 ± 2o C . A related greenhouse study where the temperatures and relative humidity fluctuated closely paralleling the outdoor conditions in Eastern Kenya Province was also carried out. T. aripo was raised on its natural diet of phytophagous cassava green mites, Mononychellus tanajoa Bondar, reared on cassava apices of young stems. Development was measured as the life history of the mite, that is, the total duration of development from egg to egg; whereas growth was determined as the duration in days it took each immature stage to change into the next stage. A coefficient of correlation between the mite developmental period or life cycle duration and relative humidity showed that there was a negative relationship between decreasing relative humidity and the length of development or duration of the mite’s life history. In other words, a decrease in the relative humidity increased the duration length of the life history which also resulted in increased mortalities. Similarly, there was a negative relationship between the fecundity or the number of offspring (eggs) produced by individual female mites with respect to lower relative humidity regimes. In this case the growth period of individual young stages was not affected by either low or high relative humidity levels. The tendency by T. aripo motile cohorts to aggregate at the fresh cassava apices than at the older or wilting ones was an indication that they were attracted to areas of high relative humidity regimes usually caused by transpiration. These findings on the relationships between relative humidity regimes and the life cycle durations of the stages of mites allows a better understanding of its population dynamics. In a similar experiment the current study has confirmed these findings. The knowledge gained will contribute to mass rearing methods of this predacious mite in greenhouse for further release in cassava fields for biological control of the cassava green mite pest.