Effectiveness of entomopathogenic fungi against peach fruit fly, Bactrocera zonata (Saunders) (Tephritidae: Diptera)

Abstract

Bactrocera zonata, commonly known as peach fruit fly, attacks a number of soft fruits such as peach, guava and mango.  For its control, entomopathogenic fungi offer a safe and efficient substitute of insecticides, which can lead to pest resistance and environmental pollution. In the present study, four entomopathogenic fungi namely Beauveria bassiana, Metarhizium anisopliae, Trichoderma harzianum and Verticillium lecanii were tested against male and female adults of B. zonata through in vitro contact bioassay at concentrations of 1×10⁴, 1×10⁶, 1×10⁸, 1×10¹⁰, and 1×10¹² cfu/ml. Mortality of B. zonata was recorded at 3, 7, 10 and 14-day post-exposure intervals. Results showed that as the concentration of spore/condial suspension of B. bassiana, M. anisopliae, V. lecanii and T. harzianum was increased from 1.0 × 10⁴ to 1.0 × 10¹² cfu/ml, LT₅₀ values were decreased from 20.45 to 8.40 , 62.85 to 16.68, 62.85 to 16.68, and 34.09 to 16.42 days for female, and 23.82 to 9.1, 63.80 to 12.65, 63.80 to 12.65 and 29.55 to 13.90 days for male B. zonata, respectively. LC₅₀ values of B. bassiana, M. anisopliae, V. lecanii and T. harzianum against B. zonata decreased from 5.17 × 10¹⁶ to 6.36 × 10⁸, 9.33 × 10¹³ to 5.58 × 10⁹, 3.02 × 10¹⁵ to 8.07 × 10¹¹and 4.00 × 10¹⁸ to 6.80 × 10¹³ cfu/ml  for female, and from 2.60 × 10¹⁵ to 3.03 × 10⁸, 2.26 × 10¹⁴ to 1.13 × 10⁹, 3.73 × 10¹⁵ to 7.04 × 10¹⁰ and 2.67 × 10¹⁹ to 1.02 × 10¹²  cfu/ml for male, respectively, over a period of 3–14 days. On the 14^th day, B. zonata males had the highest mortality (84%) due to B. bassiana at 1×10¹² cfu/ml, followed by 48%, 59% and 74% mortality due to T. harzianum, V. lecanii and M. anisopliae, respectively. In general, adult female mortality was lower than the adult male mortality. With a moderate to high mortality of B. zonata due to different fungal species, the findings of the present study show that the tested entomopathogenic fungi are highly effective in controlling this pest. Because of their high efficacy against B. zonata, the two fungal species viz. B. bassiana and M. anisopliae can be included in an IPM plan to control B. zonata.