Population dynamics of the mango seed weevil, Sternochetus mangiferae (F.) (Coleoptera: Curculionidae) in South Africa.
Graaf J. de
Author Affiliation: Westfolia Tegnologiese Dienste, Posbus 1103, Tzaneen 0850, South Africa.
27 : 30-35
Abstract : Sternochetus mangiferae (F.) is a monophagous pest of mango distributed widely from its probable origin in Myanmar and North-East India. The insect is considered a quarantine pest by the plant protection authorities of several countries, including the Peoples Republic of China and the USA. The most universal phytosanitary measure to control the pest is the establishment of pest free production sites and areas. Monitoring and an integrated approach focussing on chemical control are important measures to test for their ability to achieve and/or maintain pest free status. The aim of the study was to investigate the population dynamics of the mango seed weevil to determine the most vulnerable life stage of the pest to optimize specific timing of controls. Two orchards were monitored over seven two-week intervals from 10 October 2006 to 3 January 2007 (harvest date). Weevil occurrence was recorded on the surface of fruit (eclosed and uneclosed eggs) and in seeds (larvae, pupae, adults). Mean ambient temperatures during the study were obtained from a nearby weather station. Trees were physically shaken every two weeks to knock adults from a tree. A factorial ANOVA and post hoc Tukey HSD test was used for analysis, while a Pearson Product Moment correlation was used to relate the dependent variables with ambient temperature. Eggs were observed over 12 weeks from 10 October, and showed a long peak in November and December. Small larvae mainly occurred on 21 November, large larvae on 5 December, pupae on 19 December and adults on 3 January. The amount of data available to determine adult activity was limited, but suggested adults were most common in trees before first egg laying to middle November. Based on infestation data, Tommy Atkins mangoes were the most vulnerable to eggs laid 4-5 weeks after the first signs of oviposition, when fruit were approximately tennisball size. The susceptibility to infestation may be related to the insect and/or the fruit development stage. The life stage occurrence of S. mangiferae did not correlate with temperature, but models making use of heat units may be useful to accurately predict the timing of controls. The susceptible egg and small larval stage of the pest can be targeted by chemical and physical control measures and adult beetles can also be targeted by chemicals before oviposition.