Bulletin of Insectology 73 (1): 71-78, 2020 ISSN 1721-8861 eISSN 2283-0332 Parasitism capacity of Telenomus remus and Trichogramma pretiosum on eggs of moth pests of peanut José Ricardo Lima PINTO, Odair Aparecido FERNANDES School of Agricultural and Veterinarian Sciences, São Paulo State University (UNESP), Jaboticabal, SP, Brazil Abstract Telenomus remus Nixon (Hymenoptera Scelionidae) and Trichogramma pretiosum Riley (Hymenoptera Trichogrammatidae) are widely used for the control of lepidopteran pests in several countries, but applied programs using these parasitoids in peanuts are still rare. Therefore, the comparative parasitism capacity of T. remus and T. pretiosum in Stegasta bosqueella (Chambers) (Lepi- doptera Gelechiidae), Spodoptera cosmioides (Walker) and Spodoptera frugiperda (J.E. Smith) (Lepidoptera Noctuidae) eggs were studied under controlled conditions (12L:12D photoperiod, 25 ± 1 °C, and 70 ± 10% RH). Eggs of S. bosqueella, S. cosmi- oides and S. frugiperda were offered daily throughout the adult lifespan of the parasitoids. Both parasitoids did not parasitize eggs of S. bosqueella. Eggs of Spodoptera spp. were significantly more parasitized by T. remus than by T. pretiosum. These two parasi- toids presented the highest parasitism rate in the first 24 hours in Spodoptera eggs. However, to obtain 80% of parasitism in Spodoptera spp. took up to seven days for T. remus and up to three days for T. pretiosum. Telenomus remus demonstrated a long- er lifespan, greater number of emerged parasitoids, and a female-biased sexual ratio, which might result in a greater potential con- trol of Spodoptera spp. in the field. For S. bosqueella, other biological control agents should be considered. Key words: biological control, egg parasitoids, biological parameters. Introduction According to Faria et al. (2000) for biological pest con- trol to be successful, basic studies to evaluate biological Technological innovations in the Brazilian peanut (Ara- parameters are crucial, as they are the basis for choosing chys hypogaea L.) production chain, such as the use of the ideal control agent and assuring efficacy in a biologi- runner varieties, have provided an increase in planted cal control program. Parasitoids of the genera Telenomus area, yield and exports in recent years (MDIC, 2018). (Hymenoptera Scelionidae) and Trichogramma (Hyme- This leguminous plant is the main species used in crop noptera Trichogrammatidae) are widely used to control rotation with sugarcane in the Brazilian Southeastern lepidopteran pests, mainly because these parasitoids of region, which is responsible for about 90% of the na- eggs eliminate the pest before the damage is caused to the tional peanut production (CONAB, 2018). crop (Cônsoli et al., 2010). Thus, considering the im- The rednecked peanutworm moth, Stegasta bosqueella portance of lepidopteran pests and lack of studies on the (Chambers) (Lepidoptera Gelechiidae), and the use of egg parasitoids as biological control agents in pea- armyworms Spodoptera cosmioides (Walker) and nuts, this work aimed to evaluate the comparative parasit- Spodoptera frugiperda (J.E. Smith) (Lepidoptera Noctu- ism capacity of Telenomus remus Nixon and Trichogram- idae), are reported as the main lepidopteran insects in ma pretiosum Riley on eggs of S. bosqueella, S. cosmi- peanut crop and may cause high yield losses (Campos et oides, and S. frugiperda under laboratory conditions. al., 2010; Boiça Junior et al., 2011; 2013). These insects can cause intense defoliation with negative effect on plant development. In addition, S. bosqueella can feed Materials and methods directly on the tips of peanut vines reducing their growth and, hence, peanut production in runner varie- Host and parasitoid rearing ties. These insects are usually controlled by chemical T. remus adults were from a strain introduced from insecticides, and growers do not apply other tools to Venezuela and kept in mass rearing using eggs of control these defoliators. S. frugiperda as host, according to methodology of Parasitoids have been used worldwide in applied bio- Bueno et al. (2010b). The initial colony of T. remus was logical control programs and many successful cases established from 650.000 individuals collected in S. fru- concern the control of insect pests (van Lenteren et al., giperda egg masses in maize crop from Barquisimeto, 2018). In Brazil, successful biological control by egg Lara, Venezuela and introduced into Brazil in 2012 (Na- parasitoids in various crops, such as sugarcane, soy- ranjo-Guevara et al., 2020). The adults of T. pretiosum beans, maize, and tomato have already been reported came from Bug Biological Agents, Piracicaba, SP, Bra- (Parra, 2014), constituting an economically viable con- zil (currently Koppert Brazil - Biological Products), trol method and less harmful to the environment (Simo- where they are kept on the factitious host, Ephestia ku- nato et al., 2014). However, research on biological con- ehniella Zeller (Lepidoptera Pyralidae). A total of trol of pests in peanuts is still scarce and biocontrol is 20.000 parasitized eggs of E. kuehniella were provided not yet applied in the field. by the company and adults of T. pretiosum were used in the essays after emergence. Both parasitoids were kept to the parasitoids. Only five tubes (replicates) could be in glass tubes (10 × 2 cm in diameter) and conditioned used for each parasitoid and lepidopteran species, be- in climate chambers 12L:12D photoperiod, 25 ± 1 °C, cause the number of eggs available on daily basis from and 70 ± 10% RH. S. bosqueella was a limiting factor. This species is not Adults of S. bosqueella were collected in a pesticide- reared in artificial diet and oviposition was not enough free peanut field, brought to the laboratory and kept in for a larger number of replications. The tubes were acrylic cages (30 × 30 × 30 cm) inside climate chambers closed with clear plastic film (PVC). The cardboards 12H:12D photoperiod, 25 ± 1 °C, and 70 ± 10% RH, were replaced daily until the females died. The card- according to Boiça Junior et al. (2011). The adults were boards were transferred to similar glass tubes and main- fed with a 10% honey aqueous solution supplied in cot- tained at the controlled conditions as mentioned below ton swabs placed in the cages. Each cage had also one until the emergence of the parasitoids. After the emer- plastic cup (700 ml) containing one fifteen-day-after- gence, all parasitoids were counted and sexed using emergence peanut seedling (A. hypogaea variety ‘Gran- morphological characteristics (antennae and hind tibi- oleico’) as an oviposition substrate, which was replaced ae), as suggested by Cave (2000) for T. remus and by daily throughout the lifespan of adult moths. The plant Pinto et al. (1997) for T. pretiosum. parts containing eggs were clipped and transferred to The experiment was carried out under controlled con- plastic Petri dishes (1.5 × 9 cm in diameter). These plant ditions using climate chambers 12L:12D photoperiod, fragments were placed on double-sheet moist filter pa- 25 ± 1 °C, and 70 ± 10% RH. Longevity of experi- per to avoid egg viability reduction and favour initial mental female parasitoids, number of eggs parasitized larval development. For the studies, F2 generation eggs daily, total number of eggs parasitized per female, cu- were used. mulative percentage of parasitism (total number of para- Adults of S. cosmioides and S. frugiperda were ob- sitized eggs/total number of eggs exposed to a female tained from laboratory colonies maintained at the during its lifespan), survivorship rates of the experi- UNESP campus of Jaboticabal, SP, Brazil. Larvae were mental females, number of emerged parasitoids and sex fed an artificial diet based on beans and wheat germ ratio (number of females divided by total number of in- (Greene et al., 1976). The adults were maintained in dividuals) were determined. polyvinyl chloride (PVC) cages (21.5 × 10 cm in diame- ter), adopting a methodology proposed for rearing Ultrastructure of the lepidopteran eggs S. frugiperda (Bueno et al., 2010b). Rearing conditions, Eggs were transferred to 0.5-ml plastic microcentri- including a potted 15-day-old peanut plant, were similar fuge tubes (Eppendorf, Hauppauge, NY, USA) contain- to S. bosqueella. Eggs laid on leaves were used for the ing sodium phosphate buffer solution (0.1M, pH 7.2) tests. where they were kept for 30 minutes. The eggs were then fixed in 2.5% glutaraldehyde solution in phosphate Parasitism capacity buffer (0.1M, pH 7.2) at 4 °C for 72 hours. After this Freshly-laid individual eggs or egg masses (<24 period, the samples were washed using phosphate buffer hours) of the lepidopteran pests were removed along solution and the material was subjected to a second fixa- with the substrate (leaves or petioles) according to Faria tion using 1% osmium tetroxide solution overnight at et al. (2000). Prior to use, the eggs were counted using a 4 °C. The samples were repeatedly washed with sodium stereomicroscope (Zeiss Stemi SV6, Jena, Germany) phosphate buffer and the dehydration of the material in and the substrates fixed to a rectangular white cardboard an increasing series of ethanol concentrations (30, 50, (0.8 × 5 cm) using non-toxic white glue (Tenaz Henkel 70, 80, 90 and 100%) for 15 minutes each. The dehy- Ltd., São Paulo, SP, Brazil). Each cardboard contained drated material was critically dried (EMS-850) and then eggs of only one species: 20 eggs of S. bosqueella, 100 the stubs were prepared for gold metallization of the eggs of S. cosmioides and 100 eggs of S. frugiperda. sample in DESK II Vacuum. Eggs were than scanned Lower numbers of S. bosqueella eggs were offered be- using Scanning Electronic Microscopy (model Zeiss cause of limited availability. As Spodoptera species lay Evo MA10, Jena, Germany). egg masses with several layers, all eggs of the upper layers were removed with a thin camel-hair brush to Data analysis keep only one layer. This assured access to the host by Longevity, number of parasitized eggs, number of both parasitoid species because T.