Biology and control of the mango seed weevil in South Africa

[摘要] English: The mango seed weevil (MSW), Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae), generally causes few problems on early-season cultivars, since the fruit are marketed and consumed before adult emergence from the fruit. Adult emergence from late-hanging cultivars, however, results in unattractive lesions that influence the marketability of the fruit. There is little evidence that MSW influences yield, although some authors argue that MSW development in the seed may lead to premature fruit drop. The economic impact of the MSW is primarily based on the fact that it is a major phytosanitary pest, restricting access to new foreign markets and contributing to substantial rejections of fruit destined for existing export countries. The MSW has no natural enemies, is monophagous on mango and completes its entire life cycle within the mango seed. The impact of this pest can, therefore, be greatly reduced by orchard sanitation. Sanitation practices, however, are labour intensive, necessitating producers to rely on alternative or additive control measures. Several semi-penetrant and contact pesticides are registered for MSW control. However, with trans-laminar products it is imperative that treatments coincide with, or are applied just after, the onset of weevil oviposition. This requires intensive and accurate scouting programmes, with an in-depth knowledge regarding the duration of oviposition necessary to ensure seasonal control. When using contact insecticides, applications should coincide with seasonal and daily activity peaks to ensure direct contact. Since adult weevils are extremely inactive, this necessitates an in-depth knowledge of MSW activity patterns. It is also imperative to understand the development cycle and life strategies of the insect in order to know at which time intervention would prove to be the most effective. The product most generally used for MSW control in the Hoedspruit magisterial district of the Limpopo Province is fenthion (Lebaycid® EC 500g/�?a.i.). This product is very effective, but does not provide 100% control and can lead to secondary infestations of mango scale, Aulacaspis tubercularis (Newstead) (Hemiptera: Diaspididae), and mealybug (various species). The use of organophosphates on fruit destined for certain overseas markets is also under investigation by the EU. It is for this reason that Westfalia Technological Services, over the past four years, investigated various aspects of MSW general biology, reproduction and control. The investigation into the activity patterns of adult weevils indicated that MSW were crepuscular �?nocturnal insects. For this reason, applications with contact insecticides aimed at controlling the adult weevil would be expected to be more efficacious when applied at dusk. During the study investigating MSW development, it was found that the majority of MSW eggs hatched between 7 and 14 days, with some of the first instar larvae already having penetrated into the seeds between 7 and 14 days after oviposition, depending on whether the eggs were laid early or late in the season. This implies that chemical control with contact and semi-penetrant chemicals, aimed at controlling the MSW larvae, should preferably not commence later than 7 days after observing the first eggs in the orchards. However, it was found during the course of this study that MSW oviposition commenced during the latter part of September and continued up to the latter part of January, a period considerably longer than previously stated in the literature. For this reason, more than one chemical application would be warranted. While investigating alternative chemical control measures, it was found that a single application with the systemic insecticide, thiamethoxam (Actara�?SC 240g/�?a.i.), applied during flowering in the root zone, rendered seasonal MSW control. The use of this product, therefore, negates the necessity of tedious fruit inspections and an in-depth understanding of the pest in order to determine the most appropriate time for chemical intervention.

[发布机构] University of the Free State