Diversity and dominance of order: Diptera and Hemiptera fruit pests on papaya in two commercial farms in Weligama, Sri Lanka

Abstract

Papaya (Carica papaya) is one of the major commercial fruit crops cultivated in Sri Lanka, catering to both local and export markets. However, studies on insect pests affecting papaya and their dominance status remain limited. This study was conducted to identify insect fruit pests (IFPs) and assess their dominance level in two selected papaya farms (commercial varieties) in Weligama, Matara, Sri Lanka. The Midigama Fruit Farm (MFF) and the Weligama Urban Council’s Model Fruit Farm (WFF) were selected as the study sites. The survey was conducted from August to October in 2024, using two randomly selected sub-sampling sites (~10 m2 per site) per fruit farm. In each sampling round, five papaya trees were randomly selected. For each tree, five mature leaves and five fruits were observed for pest occurrence. Recorded insect pests were collected and identified using pictorial guides. A total of 15 IFP species were recorded, belonging to two orders: Diptera (9 species), Hemiptera (6 species). Of these, 11 insects were identified to the species level, while four were identified only to genus level (Aphid sp.2 & 3, and Bactrocera sp.3 & 4). MFF recorded 12 species (80% of total): 4 Hemipteran [33.33%] and 8 Dipteran [66.67%], while WFF recorded 14 species (93.33% of total): 6 Hemipteran [42.86%] and 8 Dipteran [57.14%]. WFF showed higher Margalef species richness (dm=1.695) and Shannon Weiner diversity (H=0.538) than MFF (dm=1.410; H=0.451). Eleven IFP species, including Paracoccus marginatus, Pseudococcus longispinus, Aleurodicus dugesii, Aphid sp.3, Bactrocera dorsalis, Bactrocera kandiensis, Bactrocera correcta, Bactrocera latifrons, Zeugodacus cucurbitae, Zeugodacus tau, and Zeugodacus caudatus were common to both farms. Icerya seychellarum, Aphid sp.2, and Bactrocera sp.4 were recorded only in WFF, while Bactrocera sp.3 was exclusive to MFF. P. marginatus was the most dominant IFP species in both farms (in MFF, D=0.518 & in WFF, D=0.432), whereas B. dorsalis showed the lowest dominance (MFF, D=0.011; WFF, D=0.010). The results indicated that WFF had a higher diversity (H=0.538) and species richness of IFPs than MFF (H=0.451), with P. marginatus (Papaya Mealybug) emerging as the most dominant pest in both farms