Tree growth losses from Gonipterus sp. 2 feeding damage on Eucalyptus plantations and quantified economic impact

Economic impact and re-establishment of biological control for <em>Gonipterus</em> sp. 2 in <em>Eucalyptus</em> plantations in South Africa data including figures, r codes, and datasets. <em>Gonipterus</em> sp. n. 2 (Coleoptera: Curculionidae), native to Australia, was reported in South Africa in 1916 and has become a serious pest in <em>Eucalyptus</em> plantations. The adults and larvae feed on young and tender leaves of <em>Eucalyptus</em> which can result in a reduction in tree growth and/or extension of rotation length and thus negatively affect economic benefits derived from plantations. Despite the economic importance of <em>Eucalyptus</em> and the threat posed by <em>Gonipterus</em> sp. n. 2, there is a lack of knowledge on the economic impact of this insect in South Africa. The main control strategy for <em>Gonipterus</em> sp. n. 2 is biological control, using a solitary egg parasitoid wasp, <em>Anaphes nitens</em> Girault (Hymenoptera: Mymarid). However, there are still outbreaks of <em>Gonipterus</em> sp. n. 2 despite the presence of this biological control agent, thus necessitating the use of alternative control measures for effective integrated pest management. In this study, the tree growth losses and corresponding economic impact of <em>Gonipterus</em> sp. n. 2 were quantified from insect exclusion trials, and the effect of cypermethrin (pyrethroid insecticide) on the re-establishment of <em>A. nitens</em> was also investigated. The insect exclusion trials consisted of chemically treated plots for the exclusion of <em>Gonipterus</em> sp. n. 2 and untreated plots for this beetle to freely feed. Results from insect exclusion trials showed that <em>Gonipterus</em> sp. n. 2 can result in a significant 17.5% (p = 0.022) reduction in wood volume from cumulative 18% defoliation of two assessment events which translates to a projected economic impact of between R6 399.22/ha (344.11 USD) and R29 224.53/ha (1571.51 USD) at harvest (8 years). The effect of cypermethrin on the re-establishment of <em>A. nitens</em> was investigated by comparing parasitism rates from chemically treated and untreated treatments, before and after spraying of  ~2-year-old (at time of last egg collection) <em>Eucalytpus dunnii</em>. <em>Gonipterus</em> sp. n. 2 egg capsules were collected from the field for assessment of parasitism rates. It was found that the insecticide did not influence the parasitism rate (re-establishment) of the parasitoid, indicating potential compatibility between biological and chemical control of <em>Gonipterus</em> sp. n. 2, although larger trials are needed to confirm the results. This is the first study in South Africa to quantify the economic impact of <em>Gonipterus</em> sp. n. 2 and the compatibility of cypermethrin (one of the most used broad-spectrum insecticides) with <em>A. nitens</em> in the field.