Reproduction of Helopeltis theivora Waterhouse (Hemiptera: Miridae) and Egg Parasitoid Characteristics of Helopeltis spp. Infesting Eucalyptus in PT Toba Pulp Lestari and PT Riau Andalan Pulp and Paper, Sumatra

Abstract

Mirid bugs of the genus Helopeltis spp. (Hemiptera: Miridae) are major pests of Eucalyptus in Indonesia. These insects attack young shoots and leaves, causing puncture marks, necrotic lesions, shoot dieback, stunted growth, and even mortality of young plants. Egg parasitoids have potential as biological control agents; however, information on their species composition, biological characteristics, and ecological roles in Eucalyptus ecosystems in Indonesia remains limited. In addition, understanding the reproductive performance of Helopeltis theivora on different host plants is essential to support insect rearing and the provision of host eggs for parasitoid studies. This study aimed to (1) compare the reproductive performance of H. theivora on two host plants, (2) identify egg parasitoids associated with Helopeltis spp. eggs on Eucalyptus in PT Toba Pulp Lestari (TPL) and PT Riau Andalan Pulp and Paper (RAPP), (3) describe the abundance, parasitism rate, and biological characteristics of egg parasitoids, and (4) analyze the main ecological factors influencing parasitism rates of Helopeltis spp. eggs. The study was conducted from May 2024 to January 2025. Reproductive performance tests of H. theivora were conducted using 20 pairs of one-day-old adults derived from the first generation (F1) of field-collected populations. The experiments were carried out on two host plants, Eucalyptus shoots and cucumber, with daily replacement of host material until female death. Observed variables included oviposition period, fecundity, daily egg production, and female longevity. Egg samples of Helopeltis spp. on Eucalyptus were collected purposively from infested trees in three TPL estates and three RAPP estates, then reared until parasitoid emergence. Parasitoids were identified based on morphological characteristics, and a dichotomous key was constructed. Observed parasitoid variables included species composition, parasitism rate, incubation period, emergence rate, sex ratio, and egg density per branch. Data were analyzed using Microsoft Excel 365 and RStudio (Version 2024.9.01+94). Reproductive performance data of H. theivora on the two host plants were analyzed using two-sample tests (t-test, Welch’s t-test, or Wilcoxon test) based on data normality and variance homogeneity. Egg density per branch was analyzed using Welch ANOVA followed by the Games–Howell post hoc test at a 5% significance level. The number of egg parasitoids was analyzed using one-way ANOVA followed by Tukey’s HSD test. In addition, Conditional Inference Tree (CIT) analysis was applied to identify the main ecological factors influencing parasitism rates based on permutation-based independence tests (a = 0.05). The results showed that the reproductive performance of H. theivora was influenced by host plant species. Individuals reared on cucumber exhibited higher fecundity (112.4 eggs/female) and daily egg production (10.6 eggs/day) than those reared on Eucalyptus shoots, indicating that cucumber is a more suitable alternative host plant for laboratory rearing of H. theivora. Egg density of Helopeltis spp. differed significantly between TPL and RAPP estates. Three egg parasitoids were recorded in this study: Chaetostricha sp. (Hymenoptera: Trichogrammatidae), Erythmelus helopeltidis (Hymenoptera: Mymaridae), and Telenomus sp. (Hymenoptera: Scelionidae). A dichotomous key was successfully developed to support identification. The parasitoid community was dominated by Telenomus sp., with the highest abundance and parasitism rate reaching 37.3%. Biologically, E. helopeltidis exhibited a shorter incubation period (8.27 days) and a higher emergence rate (44%) than the other parasitoid species. Parasitoid sex ratios were generally female-biased. CIT analysis identified parasitoid species richness as the main ecological factor influencing parasitism rates of Helopeltis spp. eggs. These findings provide important baseline information for the development of natural enemies as biological control agents against Helopeltis spp. in Eucalyptus plantations in Indonesia.