Feeding preference of pink mealybug, Phenacoccus manihoti to infestation level of four cassava varieties

Abstract

The pink mealybug, Phenacoccus manihoti is one of the most serious pest of cassava, Manihot esculenta (L.) Crantz. When this insect feeds on cassava, it causes leaf curl symptom which categorize into 5 level (0-4). The infestation level and development of the mealybug differ among cassava varieties. This study aimed to compare the amount and leaf curl level of pink mealybug on four cassava varieties: Rayong72 (RY72), Rayong9 (RY9), Kasetsart50 (KU50) and Huaybong60 (HB60). Five female mealybug was introduced to one month old cassava in net house. After 8 weeks, the highest increasing number of mealybug and leaf curl level was shown in RY72, RY9, KU50 and HB60, respectively. The RY72 RY9 and KU50 showed leaf curl level 4, while HB60 showed level 3. Honeydew excretion was measured to investigate the host preference of the pink mealybug. The highest of honeydew excretion was on RY72 followed by RY9, KU50 and HB60. Test on moving efficacy of 1st instar nymph after hatching from ovisac was observed. The ovisac was released on the 4th leaf (bottom). The fastest movment to the 1st leaf (top) within 7-8 days was in RY72 and HB60, respectively, while on the other two varieties mealybug stayed on the initial leaf. Pink mealybug infestation also affected the yield and starch percentage of cassava. The yield of RY72 and HB60 was less than KU50 and RY9. The percentage of starch in RY72 was significant lower than the other cassava varieties.