Identity and Population Density of Thrips hawaiiensis (Insecta: Thysanoptera) in Conventional “Magallanes” Pummelo Orchard in Carmen, Davao del Norte, Philippines

Abstract

A conventional “Magallanes” Pummelo orchard in Brgy. Minda, Carmen, Davao del Norte, Philippines was selected to assess thrips species composition, population density, and associated natural enemies. The insecticide treated pummelo orchard was situated adjacent to vast Cavendish banana plantations. Thrips were collected weekly from September 2017 to July 2018 from five different randomly selected flowering pummelo trees by destructive sampling and yellow sticky trap methods. Thrips were sorted and examined under the microscope. Findings of the study showed that Thrips hawaiiensis (Morgan), (Thripidae: Thripinae) was the only species of thrips infesting “Magallanes” pummelo. This constitutes the first report in this host variety. Thrips hawaiiensis population fluctuated within the six phenological stages of pummelo fruiting cycle but was significantly high at the peak of flowering stage. Population started to decline at petal fall and fruit development stages although the pummelos still produced small numbers of new terminal shoots. These shoots provided stable food source for remaining thrips larvae. Population was significantly low when the fruits are at harvestable stage (p < 0.01). Among the weather variables monitored temperature had very low coefficient value (r = 0.09) with a positive relationship to thrips population; however, together with rainfall and relative humidity, statistical significance value did not significantly (p > 0.05) influence thrips population. Furthermore, absence of parasitoids during the whole duration of the study may have been affected by the conventional pest management continuously being practiced by plantation owners of using broad spectrum insecticides that may have affected the non-target species in the area.