Effect of fungal infection on reproductive potential and survival time of Tetranychus urticae (Acari: Tetranychidae)

Abstract

The effect of fungal infection on the reproductive potential of two-spotted spider mite, Tetranychus urticae, was evaluated as part of the full biocontrol potential of three entomopathogenic fungi by modeling of fecundity probability. Female mites (<or=2-day-old) on leaves were exposed to the sprays of Beauveria bassiana, Paecilomyces fumosoroseus and Metarhizium anisopliae at the concentrations of 1.13 x 10(3), 1.55 x 10(3) and 0.95 x 10(3) deposited conidia mm(-2) and then individually reared at 25 degrees C and 12:12 L:D for oviposition. Mite mortalities 10 days after spraying were 73.1, 75.4 and 67.9% in the fungal treatments versus 15.5% in control. On average, females infected by the three fungal species survived 5.8, 6.2 and 6.3 days, and laid 3.1, 4.0 and 4.0 eggs per capita, respectively. These were 3-4 fold lower than the control fecundity at 12.3. The cumulative probabilities [P(m <or= N)] for the counts of infected and non-infected (control) females laying m eggs per capita (m <or= N) during 10 days fit very well the equation P(m <or= N) = 1/[1 + exp(a + bm)] (r(2) >or= 0.98), yielding a solution to the probability for the female mites to achieve a specific fecundity {P(m <or= N)-P[m <or= (N - 1)]}. Consequently, the infected mites had 71-78% chance to lay <or=5 eggs per capita but only 5-8% to deposit >10 eggs despite some variation among the tested fungi. In contrast, the chances for the non-infected mites to achieve the low and high fecundities were 23 and 55%. The fitted probabilities provide a full coverage of the fecundity potential of infected versus non-infected mites and are more informative than the mean fecundities.