First occurrence of Spodoptera cosmioides (Walker, 1858) (Lepidoptera: Noctuidae) on eucalyptus seedlings after in field transplantation, in the Rio Grande do Sul State, Brazil

This study reports the first occurrence of Spodoptera cosmioides (Walker, 1858) (Lepidoptera: Noctuidae) larvae causing defoliation in transplanted seedlings in a clonal plantation of Eucalyptus urophylla S.T. Blake (Myrtaceae), in Butiá municipality, Rio Grande do Sul State (30°9’45” S; 51°59’42” W). The S. cosmioides caterpillars are polyphagous, including eucalyptus among their host plants. It was observed that the caterpillar infestation damaged 80% of the seedlings, while the defoliation varied from 13% to 24% per plant. This is the first record of S. cosmioides caterpillars causing injuries in a new plantation of E. urophylla.

In Rio Grande do Sul State, the occurrence of some insect pests were reported in eucalyptus seedlings settled at the field. Diloboderus abderus (Sturm, 1826) (Coleoptera: Melolonthidae) was reported damaging the plant root collar of clonal seedlings of E. grandis Hill ex Maiden x E. urophylla S. T. Blake (Garlet et al. 2009) and Heilipodus dorsosulcatus (Boheman, 1843) (Coleoptera: Curculionidae) damaging the apical portion of the seedlings of E. saligna Smith and hybrid clones of E. urophylla x E. grandis (Garlet et al. 2011).
The present work reports, for the first time, the occurrence and damage of S. cosmioides larvae in field transplanted E. urophylla seedlings in a commercial plantation in Rio Grande do Sul State, Southern Brazil.
The attack by S. cosmioides larvae was verified in a one-monthold commercial plantation of E. urophylla (AEC 0144 clone) in Cambará garden forest (30°9'45" S; 51°59'42" W), at a parcel identified as 009A (25.4 ha), belonging to the company CMPC, at Butiá municipality, Rio Grande do Sul. Planting was performed on November 3, 2015, using a spacing of 3.0m x 2.5m, with a density of 1,334 plants/ha. A survey of the attack intensity was performed in the studied area by evaluating five randomly distributed 100-plant parcels.
The caterpillars (Fig. 1A) were collected with the aid of tweezers, packed in plastic containers with small holes, and transported to the laboratory of Universidade Federal de Santa Maria (UFSM), Santa Maria, Rio Grande do Sul, for raising and later identification. The 20 collected specimens were kept in plastic pots covered with voile, where they remained in a controlled environment (temperature of 25 o C ± 1°C, air relative humidity of 70% ± 5%, and 12-hour photoperiod) until the adult emergence (Fig. 1B). The caterpillars fed only eucalyptus leaves in the laboratory and completed the life cycle until the adult phase of the insect, evidencing that the eucalyptus is a potential host for the pest.
In this area of attack, the eucalyptus plantation has been carried out for more than 30 years, while its surrounding areas are used for agriculture and livestock. The first attack was recorded on December 1, 2015 (Figs. 1C, 1D). The feeding was performed only with eucalyptus leaves until the pupal stage. The species was identified as S. cosmioides by a specialist in the area. The voucher specimens are deposited in the collection of the Forest Entomology Laboratory of the UFSM. The fact that this caterpillar is polyphagous and feeds on several hosts, and that the area planted in nearby agricultural areas may have attracted the adults of S. cosmioides to oviposit in the eucalyptus plantation. As a consequence, after the eclosion, the larvae damaged the plants. It was observed that the larvae of S. cosmioides caused defoliation at the border or inside of leaves of eucalyptus plants. Defoliation occurred on both new and old leaves (Figs. 1C, 1D).

Scientific Note
The severity of damage was estimated by the percentage of defoliation of each plant. In 500 evaluated plants, the average severity was 13% defoliation, with maximum defoliation rate reaching 24%. According to Tang et al. (2006), the defoliation causes water loss around the injury, decreasing the foliar photosynthetic area even more, besides reducing the foliar area for performing the photosynthesis and reducing the accumulation of photoassimilates.
The reduction in the foliar area by caterpillars may compromise the seedling settling and development soon after planting, especially for species as S. cosmioides that presents great potential for defoliation (Santos et al. 2010). S. cosmioides has a high capacity for leaf consumption. In a study comparing the potential leaf consumption between different Lepidoptera pests in soy crops, S. cosmioides consumed twice the leaf area consumed by Anticarsia gemmatalis Hübner, 1818, Pseudoplusia includens (Walker, 1857), S. eridania or S. frugiperda (Lepidoptera: Noctuidae) (Bueno et al. 2011).
Given the defoliation capacity and the population density of S. cosmioides, the occurrence of this species in E. urophylla is a new and relevant fact for eucalyptus cultivation in Rio Grande do Sul State and in Brazil. Concerning the high infestation mentioned, the reproductive capacity of the species stands out, in which females of S. cosmioides, under ideal laboratory conditions, can generate more than five thousand larvae, resulting in an estimated biotic potential of about five sextillions individuals/female/year (Specht & Roque-Specht 2019). It is possible to obtain from 9.6 to 11.7 annual insect generations in ideal temperature ranges, between 25°C e 28°C (Bavaresco et al. 2002).
Thus, as a basis for implementing adequate pest management, plantation monitoring must be constant, mainly in the initial phase. S. cosmioides is a potential pest insect for eucalyptus crop, stressing E. urophylla, which was identified in the present study as host species. Hence, given the polyphagous characteristic of S. cosmioides, constant monitoring is advisable, as well as the performance of studies involving measures to prevent the attack of the pest. The use of chemical or mechanical weeding in eucalyptus crop areas may be used to eliminate invasive plants characterized as potential hosts of S. cosmioides.
There are no registered products for controlling S. cosmioides in the eucalyptus culture (AGROFIT 2020). Therefore, testing biological insecticides based on pathogenic fungi, such as Beauveria bassiana (Bals.) Vuill. and Metharizium anisopliae (Metsch.), as well as virus entomopathogenic Baculovirus, (i.e., all pathogens that act in the natural biological control of caterpillars in the complex Spodoptera; Teodoro et al. 2013) is recommended. Such biological insecticides meet the requirements of forest certification, which has encouraged the implementation of more sustainable techniques and decisions in the management of pests in forest plantations in Brazil (Lemes et al. 2017).

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