Management of Chinese Rose Beetle (Adoretus sinicus) Adults Feeding on Cacao (Theobroma cacao) Using Insecticides

Abstract

The Chinese rose beetle (Adoretus sinicus Burmeister (Coleoptera: Scarabaeidae)) is an introduced, widely-established pest in Hawai’i. The adult beetles feed on the leaves of cacao (Theobroma cacao L.), which can lead to defoliation and even death of young trees. We evaluated the impact of five commercially available products with different active ingredients (imidacloprid, azadirachtin, Beauveria bassiana (Bals.-Criv.) Vuill., kaolin clay, and pyrethrin) and the presence or absence of weed mat cover in reducing adult beetle feeding on sapling cacao in the field. The use of weed mat cover reduced feeding damage compared to the untreated control, as did foliar application of imidacloprid, azadirachtin, and B. bassiana. In the laboratory, field-collected adult beetles were presented cacao leaf samples dipped in one of the five products and compared to a control. Beetles exposed to pyrethrin died rapidly. Among the other treatments, only exposure to imidacloprid significantly reduced survival relative to the control. Beetles fed very little on leaf samples with azadirachtin but their longevity was not significantly reduced. Imidacloprid, azadirachtin, and weed mat application had the most promise for reducing adult Chinese rose beetle feeding damage in young cacao and deserve further investigation for successful management of this significant pest.

A scarab beetle (Coleoptera: Scarabaeidae) causes tree mortality, delayed growth, and yield reduction in cacao with genotype‐specific susceptibility to herbivory

“…One notable case is the Rutelinae beetle A. sinicus, recognized as a significant cacao pest in Hawaii. 8,22 The Chinese rose beetle inflicts severe leafskeletonizing attacks, hindering tree growth and causing the demise of newly established cacao plants. This corresponds with our observations for L. femoratus.…”

“…Notable examples include the lepidopterans Anomis leona Schauss, Earias biplaga Walker (Noctuidae), Oiketicus kirbyi, Oiketicus geyeri (Psychidae), Sibine nesea (Limacodidae), certain Tortricidae, and the leaf cutter ant Atta sp., known for their potential to cause severe defoliation in cacao. [6][7][8] Even though foliar herbivory by insects affects cacao plant development due to the consumption of photosynthetic tissue and the reduction of photosynthesis, 9 little is known about the effect of defoliators on cacao tree development and yield. In fact, a limited number of studies have addressed the relationship between herbivory damage and production loss in woody crops.…”

“…The high herbivory rate caused the death of a considerable number of young plants, exhibiting a distinct leaf-skeletonizing pattern similar to the damage caused by the Chinese rose beetle, Adoretus sinicus Burmeister, in cacao orchards in Hawaii. 8,22 Adoretus sinicus adults are active at night and consume large quantities of cacao leaf surface, resulting in leaf skeletonization and defoliation to the extent that it is considered the most severe pest of young cacao in the islands. 22 In this study, we provide empirical evidence of L. femoratus as a defoliating pest of cacao.…”

“…Among them, some defoliating insects have gained interest as they primarily feed on tender leaves, delaying plant growth or causing the death of young trees. Notable examples include the lepidopterans Anomis leona Schauss, Earias biplaga Walker (Noctuidae), Oiketicus kirbyi , Oiketicus geyeri (Psychidae), Sibine nesea (Limacodidae), certain Tortricidae, and the leaf cutter ant Atta sp., known for their potential to cause severe defoliation in cacao 6–8 . Even though foliar herbivory by insects affects cacao plant development due to the consumption of photosynthetic tissue and the reduction of photosynthesis, 9 little is known about the effect of defoliators on cacao tree development and yield.…”

“…The plot, representative of the cacao‐growing system in the region, was established as part of a breeding program to evaluate the performance of different genotypes under local soil and environmental conditions. The high herbivory rate caused the death of a considerable number of young plants, exhibiting a distinct leaf‐skeletonizing pattern similar to the damage caused by the Chinese rose beetle, Adoretus sinicus Burmeister, in cacao orchards in Hawaii 8,22 . Adoretus sinicus adults are active at night and consume large quantities of cacao leaf surface, resulting in leaf skeletonization and defoliation to the extent that it is considered the most severe pest of young cacao in the islands 22 …”