Effects of spirodiclofen on the reproductive potential of two-spotted spider mite (Acari: Tetranychidae) ovipositing females

Abstract

A laboratory bioassay was conducted to evaluate the effects of spirodiclofen on the survival and reproduction of young and mated females of two-spotted spider mite (Tetranychus urticae Koch). The females were sprayed with a series of acaricide concentrations (96, 48, 24, 12, and 6 mg/l) 24-30 h after adult emergence, i.e., at the age most likely to exhibit dispersal behavior and close to their reproductive maximum. The proportions of T. urticae females that survived treatment without symptoms of poisoning were concentration-dependent, ranging between 0.41 and 0.88 (0.96 in the control). With the exception of females that survived 6 mg/l, fecundity of the treated female mites was strongly affected during the exposure, compared to the control. The mean daily fecundity (EL) and mean daily fertility (EH) of surviving females, transferred daily to new leaf disks over the following five days, significantly decreased as spirodiclofen concentrations increased. In treatments with 6 mg/l and 12 mg/l, only the latter concentration significantly reduced both EL and EH, compared to the control. In females that survived 24 mg/l and 48 mg/l, these life history parameters were reduced by over 90%, while treatment with 96 mg/l completely terminated egg-laying. The treated females lived for a significantly shorter time than untreated ones, with the exception of females that survived 6 mg/l. Compared to the control females, gross fecundity (GL) and gross fertility (GH) of the treated females were strongly reduced on the first and second day; from the third day onward, females treated with the lowest concentrations achieved marked recovery, their GL and GH going even above the values in the control. However, net fecundity (NL) and net fertility (NH) of all treated females decreased considerably throughout the trial, indicating that survival rates of these females were lower, compared to the control. Calculated as total sums of gross and net daily schedules within five days, fecundity and fertility significantly decreased as spirodiclofen concentration increased. The two lowest concentrations failed to achieve a significant reduction of GL, while GH, NL, and NH were significantly lower than control values starting with the females treated with 6 mg/L. A high percentage of unhatched eggs, especially during the initial two days after treatment (35-100%), further contributed to the significant reduction in fertility of the females treated with spirodiclofen. All concentrations of spirodiclofen significantly reduced the instantaneous rate of increase. Regression analysis showed a linear population decline with increased acaricide concentrations (y = 1.13 - 0.24x; R2 = 0.91, p < 0.05)

EFFECTIVENESS OF PLANT EXTRACTS FOR THE CONTROL OF RED MITE (Raoiella indica HIRTS) IN THE COCONUT TREE (Cocos nucífera L.)

“…On the other hand, the chemical product Spirodiclofen presented one of the highest LC 50 , with 38.8637 ml/L (Table 1) and could develop resistance by the red mite. Montoya et al (2017) tested this chemical product on adult females of T. urticae and found that it has slow effectiveness, while Marcic et al (2009) point out that mortality is lower within the first 48 hours.…”

Side effects of insecticides alone or in a mixture with acaricide on life history traits and demographic parameters of Brevipalpus yothersi

“…The sublethal effect is the name given to this response. It may be manifested as reductions in life span (Shen et al 2021), development rates (Bozhgani et al 2018), fertility (Marcic et al 2009), fecundity (Amaral et al 2019), and changes in behavior such as feeding (Holland et al 1994), and oviposition (Marcic et al 2007). Thus, insecticides alone or in a mixture with acaricides can exert subtle and overt effects that must be considered when examining their impact on the B. yothersi population.…”