Improved artificial diet for life history study and bioassay of the Philippine population of eggplant fruit and shoot borer, Leucinodes orbonalis Guenee (Lepidoptera:Pyralidae)

In search for an efficient bioassay protocol suited for the Philippine population of eggplant fruit and shoot borer (EFSB), Leucinodes orbonalis Guenee, four bioassay protocols were initially evaluated. Two bioassay protocols used detached plant parts (eggplant leaf disc, eggplant fruit chip) while the other two used artificial diet media (Patil artificial diet (PAD) and multiple insect diet pre-mix (MID) by Southland Products Inc.). Results obtained from all four bioassay protocols showed that percent larval mortality in control groups (66.67 to 85.56%) exceeded the 10% allowable limit set by the Insecticide Resistance Action Committee (IRAC). However, higher percent larval survival was observed in the artificial diet bioassays (68.89 to 85.56%) compared with the values obtained using detached plant parts bioassays (66.67 to 85%). Further modifications of PAD (MPAD A to MPAD C) and MID (MMID A to MMID E) were formulated by varying the proportions of the main ingredient (e.q. blackgram in PAD) and/or adding supplements namely bee pollen, eggplant fruit powder, eggplant calyx powder singly or in combination. EFSB neonates were reared in each modified artificial diets in replicated trials and their percent survival and weight gain were recorded. Results showed higher percent larval survival in the modified diets (86 to 96.67%) than their original formulations. Among the diets tested, the highest percentage of larval survival and weight gain were recorded in EFSB neonates reared in MMID E. Percent larval mortality in control group reared in MMID E was lower (approximately 4%) than IRAC's 10% allowable limit. To evaluate further the suitability of MPAD C and MMID E for eggplant fruit and borer (EFSB) studies, two studies were conducted: EFSB life history study and EFSB dose-response to Cry1 AC concentrations. Results obtained in the EFSB life history study showed that EFSB successfully completed their life cycles when reared in both diets. On the average, EFSB reared in MMID E showed 32.36 days total developmental period, 82.22% pupation and 75.55% adult emergence. EFSB reared in MPAD C showed shorter developmental period (23.09 days) and less than 50% pupation (46.67%) and adult emergence (34.45%) indicating that MMID E is more suitable artificial diet and developmental host for EFSB. Results from the dose-response Cry1 AC bioassay showed that percent larval mortality of the control group of EFSB reared in both diets did not exceed the 10% allowable limit and negative effects on larval weight were not observed. Using MMID E diet, a dose-response regression line was established and LC50, LC90 and LC95 values were estimated. Based on the results obtained in this study, the modified multiple insect diet E (MMID E) proved to be the most suitable artificial diet for mass rearing and bioassay applications of the Philippine EFSB populations tested.