Pg. 18-22 Progress with litchi moth research

Quantification of peak oviposition is crucial for litchi moth control as it will determine the application timing of contact insecticides. First eggs were observed during mid November 2007, but the majority of oviposition took place when the fruit began to color noticeably. The best time for a contact insecticide would therefore be towards the end of November annually. Due to Last Cali’s mode of action, an earlier application is suggested. Last Call was evaluated on a 10 ha Wai Chee litchi farm, just outside Nelspruit. Infestation on the farm was significantly less than the previous season. The probability of the pheromone plume emanating from the treated plot (8 ha) affecting adjoining untreated plots is a distinct possibility and this trial should probably be repeated for another season to confirm these results. The insecticide trial was replicated in both the treated (Last Call) and untreated plots and despite a very low infestation, triflumuron SC appeared to be the superior product. It was positively proven that the coconut bug fed on litchis. While mature fruit are apparently not affected, significant abortion of immature fruit was recorded (averagee ±21%; range 16 – 32%). While the ability of subtropical fruit trees to compensate for early crop loss is unquestionable, the amount of early bug induced abortion that can be tolerated before economic losses ensue, still has to be determined experimentally. For macadamias it has been proven that mouthparts of the bugs introduce an array of opportunistic saprophytic fungi into the kernels. The effect of coconut bug feeding on post-harvest shelve life of the fruit is also a factor that needs clarification. A gross margin analysis revealed that significant infestation (±1 – 6%) of the litchi moth could be tolerated before the application of any corrective spray is economically justifiable on fruit destined for the internal market.

Summary:

• Litchi moth (Cryptophlebia peltastica) is a dominant tortricid moth affecting litchis in South Africa, alongside false codling moth (Thaumatotibia leucotreta), with generally low infestation levels but occasional localized outbreaks.
• Peak oviposition (egg laying) occurs as fruit begin to color, making late November the best time for applying contact insecticides to control the moth.
• A field trial using the pheromone-based product Last Call on a 10 ha Wai Chee litchi farm showed reduced infestation, but pheromone plume effects on control plots need further confirmation with repeated trials.
• Triflumuron SC insecticide showed the best efficacy among tested chemicals for controlling litchi moth larvae.
• Coconut bugs feed primarily on litchi seeds rather than the fruit flesh, causing significant early fruit abortion—on average 21% of immature fruit were aborted due to bug feeding.
• The economic threshold for litchi moth control is about 6% infestation; spraying below this level may not be economically justified for fruit marketed internally in South Africa.
• Effective control strategies include pheromone disruption, insect growth regulators, and selective insecticides, with a preference for environmentally-friendly options with short residual effects.
• Regular monitoring during the critical period starting mid-November is recommended, using pheromone traps and fruit inspections for eggs and early larval damage.
• Spray coverage is critical, requiring thorough application to reach all fruit for effective control.
• The economic analysis showed that current levels of litchi moth infestation usually do not justify routine insecticide application, but farms with histories of severe outbreaks should spray when necessary.
• The study highlights the importance of integrated pest management to sustain environmentally responsible litchi production while managing quarantine pest risks.