Biology of Scymnus (Pullus) trukensis Chapin (Coleoptera:Scymninae) on Pentalonia nigronervosa Coquerel (Hemiptera:Aphididae)

The biology of Scymnus trukensis Chapin on Pentalonia nigronervosa Coquerel was studied. The eggs were laid in cracks and crevices of the sliced banana stalks among aphid exuviae, either singly or in batches of two to three. The eggs hatched within 2-4 days period. The total number of eggs laid by a female throughout its oviposition period ranged from 22 to 156 while eggs laid per day ranged from 1 to 29. Hatchability of eggs was 50 to 100 percent. The predator passed through four larval stages. All the larval instar had a cottony and waxy exudations except for th first larval stage. The durations of the stagia were: first stadium, one day; second stadium, 1-2 days; third stadium, 1-2 days; and fourth stadium, 1-2 days. The total larval period ranged from 4 to 8 days. The pupal period ranged from 3 to 4 days. Total life span of adult males ranged 27 to 60 days and of females, 28 to 60 days. The total developmental period from egg to adult stage ranged from 7 to 11 days. Percentage survival of the first three larval stages was higher than the fourth and pupal stages. Longevity of the female and male adult was more or less the same. The functional response of the different life stages at 5, 10, 15, and 20 prey densities was determined. The mean number of aphids consumed increased with increasing prey density. The same trend was observed during the entire larval period and during a 30-day test period with adult females and males. The voracity of S. trukensis per life time varied from the 318 to 440 aphids for the male and from 370 to 608 for the female. The field population of S. trukensis was at its peak during months when the amount of rainfall and the number of rainy days were minimal; temperature and relative humidity, constant. Other Scymninae species found together with S. trukensis and also feeding on P. nigronervosa on banana were: Scymnus sp., S. frontalis (Pullus) quadripustulatus (Herbst) and Acarinus philippinensis Kapur. Five species of mites were also noted, namely, Caloglyphus sp. (Acaridea), Lesioseonus sp. (Ascidae), one unidentified species each belonging to the Acaridae, Anoetidae and Laelapidae. These mites are probably predators of the eggs of S. trukensis. A species of chalcid wasp was also observed emerging from the pupae of S. trukensis resulting to reduced survival rate