Optimal pheromone trap density for mass trapping cacao mirids

Abstract

Sahlbergella singularis Haglund and Distantiella theobroma (Distant) (Heteroptera: Miridae) are the key insect pests of cacao in Ghana and elsewhere in West Africa. Since 1954, spraying with synthetic insecticides has been the principal means of controlling these pests. In West Africa, environmental concerns, economic stimuli, and unreliable access to insecticides have stimulated interest in ecologically more benign mirid control strategies as an alternative to a total reliance on insecticides. Males of both mirid species, and those of the less damaging Bryocoropsis laticollis Schumacher, respond to the same synthetic sex pheromone blend, so pheromone‐based strategies may provide control as well as monitoring opportunities. Pheromone traps were deployed for 3 months at nine densities between two and 30 traps per 0.1 ha plot (20–300 traps ha−1) plus an untreated control treatment in a replicated large‐scale field experiment on mature mixed Upper Amazon hybrid cacao in Ghana, in order to determine the optimal dispenser density for mass trapping, lure‐and‐kill, and/or lure‐and‐infect. At the end of the trapping period, mirid populations in the various treatments were assessed by insecticide knockdown on 400 trees and by searches to hand height on 1 200 trees, together with an assessment of mirid damage. In total 781 S. singularis and 235 D. theobroma were captured in the pheromone traps. The optimal dispenser density for S. singularis was 150 traps ha−1. Over 300 traps ha−1 was probably optimal for D. theobroma as a smaller proportion of the population was captured, and numbers caught per trap displayed no decline with increasing trap density. From insecticide knockdowns, mirid population density was estimated at 220–230 ha−1, 63% of which were D. theobroma. Too few pods and orthotropic shoots were damaged by mirids to establish the efficacy of pheromone trapping for mirid control.

Effect of lure age and blend on sex pheromone trap catches of the mirid Sahlbergella singularis on cacao in Ghana

“…Only four Distantiella theobroma were trapped in this study. The low numbers here and in our previous studies at Akwadum (Sarfo et al, 2018a) and Acherensua (Sarfo et al, 2018b), probably reflects a fall in its abundance in Ghana first suggested by Owusu-Manu (2002) and since confirmed from an analysis of 34 years monitoring data of mirids from the Eastern Region of Ghana by Adu-Acheampong et al (2017).…”

Optimization and field demonstration of the Lygus pratensis (Hemiptera: Miridae) sex pheromone

“…Pheromone‐based traps, aerosol dispensers or pheromone lures can occasionally be used for mass‐trapping or mating disruption, thus contributing to a varying extent to pest control in certain crop × pest systems 41‐43 . Pheromone trap captures—at a limited number of field sites—were in accordance with field‐level L. pratensis abundance, with capture rates lower in insecticide‐treated cotton fields (< 25 males per week) (Fig.…”

Untitled

“…Traps baited with pheromone lures will be helpful in early detection of pest, mating disruption and timing of management procedures based on threshold 10 . Mass trapping of cocoa mirids has been efficiently done by pheromone trapping 11 .…”