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

• Published in: Archives of biological sciences Vol. 61; no. 4; pp. 777 - 785
• Main Authors: Marcic, D., Ogurlic, Irena, Peric, P.
• Format: Journal Article
• Language: English
• Published: University of Belgrade, University of Novi Sad 2009
• Subjects: population growth; reproduction; spirodiclofen; survival; Tetranychus urticae
• ISSN: 0354-4664; 1821-4339
• DOI: 10.2298/ABS0904777M

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).
Efekti spirodiklofena na prezivljavanje i reprodukciju mladih i oplodjenih zenki obicne paucinaste grinje (Tetranychus urticae Koch) ispitivani su u laboratorijskom ogledu. Zenke su prskane serijom koncentracija akaricida (96, 48, 24, 12 i 6 mg/l) 24-30 h nakon pojave adulta, tj. u uzrastu bliskom reproduktivnom maksimumu, kada je najveca verovatnoca za disperziju. Proporcija zenki T. urticae koje su prezivele tretman bez simptoma trovanja zavisila je od koncentracije i kretala se izmedju 0.41 i 0.88 (0.96 u kontroli). Sa izuzetkom zenki koje su prezivele 6 mg/l, fekunditet tretiranih zenki bio je znatno umanjen tokom ekspozicije, u poredjenju sa kontrolom. Srednji dnevni fekunditet (EL) i srednji dnevni fertilitet (EH) prezivelih zenki, prebacivanih dnevno na nove lisne isecke tokom pet dana, znacajno su se smanjivali kako se koncentracija povecavala. U tretmanima sa 6 mg/l i 12 mg/l, samo je ova druga koncentracija znacajno redukovala i EL i EH, u odnosu sa kontrolu. Kod zenki koje su prezivele 24 mg/l ili 48 mg/l ovi zivotni parametri bili su redukovani za preko 90%, dok je tretman sa 96 mg/l potpuno prekinuo polaganje jaja. Tretirane zenke zivele su znacajno krace od netretiranih, osim zenki tretiranih sa 6 mg/l. U poredjenju sa kontrolom, bruto fekunditet (GL) i bruto fertilitet (GH) tretiranih zenki bili su znatno smanjeni prvog i drugog dana posle tretiranja; od treceg dana nadalje, zenke tretirane nizim koncentracijama vidno su se oporavile a njihove GL i GH vrednosti bile su cak i iznad odgovarajucih vrednosti u kontroli. Medjutim, neto fekunditet (NL) i neto fertilitet (NH) svih tretiranih zenki bili su znatno umanjeni za sve vreme trajanja ogleda, sto ukazuje na umanjenje stopa prezivljavanja. Izracunati kao ukupna suma dnevnih bruto i neto vrednosti, fekunditet i fertilitet tretiranih zenki znacajno su opadali sa povecanjem koncentracija spirodiklofena. Dve najnize koncentracije nisu ostvarile znacajnu redukciju GL, dok su GH, NL i NH bili znacajno nizi kod svih tretiranih zenki. Visok procenat neispiljenih jaja, posebno u prva dva dana posle tretiranja (35-100 %) dodatno je doprineo znacajnoj redukciji ukupnog fertiliteta zenki tretiranih spirodiklofenom. Sve koncentracije akaricida znacajno su redukovale trenutnu stopu rasta populacije. Regresiona analiza pokazala je linearno opadanje populacije u zavisnosti od povecanja koncentracije spirodiklofena (y = 1.13 - 0.24x; R2 = 0.91, p < 0.05).