احتمال گروه‌گرایی کنه تارتن دولکه‌ای Tetranychus urticae Koch درحضور کنه‌های شکارگر Neoseiulus californicus وAmblyseius swirskii

Grouping ,a counterattack strategy has rarely been studied in mites especially as they are mostly dependent on volatiles in their interactions. In two spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), webbing and grouping behavior have been proven to increase survival rate in risk. we studied the grouping probability of this species in the presence of phytoseiid predators, Neoseiulus californicus and Amblyseius swirskii. The risk situations were prepared at four levels i.e. zero (no predator), low (traces), medium (one predator and two eggs) and high (one predator and five eggs). The experimental arenas were consisted from circle bean leaves, (upside down) three cm in diameter on water saturated sponge in Petri dishes (9 cm in diameter) which put in controlled conditions in germinator. Ten hours prior to experiment, we inserted the predator in arenas to start foraging. At first, five same-aged female spider mites were added to the arena and their individual locations were recorded for two and half hours every 30 minutes with water color. After 24 hours, the last spider mite location was checked alongwith the oviposition rate. 20 replicates were performed. In continue, we assessed the impact rate of the predators with spider mites in two grouping (four mites with one mm. in square position) and single (four mites each on a quarter circle) situations. The experiment was started by releasing the same-aged predator female individuals on the central point of arena and the time at which the first legs of predator touched the spider mite was recorded in addition with the first successful attack. This was monitored for the first two hours every five minutes and for the next one hour every 20 minutes. 15 replicates performed. Data analyzed through SPSS25 within oneway ANOVA and t student experiments. Results showed that in the presence of A. swirskii, the mean distance among the spider mites at the end of the third monitoring phase (cm, considering SE) was significant between control (2.03 ± 0.17) and the low risk patches (2.83 ± 0.18 , P<0.05) and the least oviposition rate was recorded from high risk patches (14.05 ± 1.68, P<0.01). When the interaction happened with the presence of N. californicus, the mean distance among the spider mite individuals was not significant (P>0.05) while the highest oviposition rate was recorded in control patches (27.45 ± 1.18). The grouping presence of spider mites did not increase the impact probability in the presence of neither of predator species (P>0.05). Results showed that the sptted spider mite was not able to decrease the predation risk through the grouping behavior although perceiving the risk would affect the oviposition process. It seems that this behaviour could change due to the risk type and predator species.