Bulletin of Insectology 73 (1): 111-116, 2020 ISSN 1721-8861 eISSN 2283-0332 Biology and life table of Stethorus tridens fed Tetranychus bastosi on physic nut Jessica Faria COSTA, Cláudia Helena Cysneiros MATOS, Carlos Romero Ferreira de OLIVEIRA, Gabriel Alves dos SANTOS Universidade Federal Rural de Pernambuco, Unidade Acadêmica de Serra Talhada, PE, Brazil Abstract This study provides information about the life cycle of the predator Stethorus tridens Gordon (Coleoptera Coccinellidae), and its potential to control the pest Tetranychus bastosi Tuttle, Baker et Sales (Acari Tetranychidae). Life table parameters of S. tridens fed T. bastosi infesting physic nut (Jatropha curcas L.) were evaluated. The mean life cycle of S. tridens was 12.35 days and mean longevity was 57.1 days, with an average of 101.1/female. The life table parameters of S. tridens were: specific fertility came to a maximum of 2.49 eggs; survival probability: 0.92%; net reproduction rate: 53.05 individuals; average generation time: 17.09 days; intrinsic rate of growth: 0.23 females/day; finite rate of increase: 1.26 individuals/female; and population doubling time: 2.98 days. These results indicate that S tridens develops successfully when fed T. bastosi on J. curcas. Key words: biological parameters, Jatropha curcas, Stethorini, red spider mite, Tetranychidae. Introduction Driesche (1999), there are several approaches to evalu- ate the impact of natural enemies on biological systems, Coccinellids of the genus Stethorus Weise (Coleoptera and one is life table construction and analysis. Coccinellidae) are specialist predators of tetranychid In this context, the development and fertility life table mites (Putman, 1955), and they forage on a wide range parameters of S. tridens fed with the pest mite T. bastosi of cultivated plants on which tetranychids are abundant on J. curcas were evaluated. We tried to answer to the (Biddinger et al., 2009). Several species have been re- following questions: (i) Does the predator can develop ported to be effective biological control agents mainly successfully feeding on T. bastosi on jatropha plants? due to their voracity, adult longevity and ability to mi- (ii) Does the predator show greater population growth grate to agricultural crops (Chazeau, 1985; Rott and compared to the pest? Ponsonby, 2000; Biddinger et al., 2009). Tetranychid mites are considered the main pest mites for infest several economically important crops. Among Materials and methods spider mite species, Tetranychus bastosi Tuttle, Baker et Sales (Acari Tetranychidae) is the most important phys- Rearing T. bastosi and S. tridens ic nut (Jatropha curcas L.) mite (Sarmento et al., 2011; Populations of the predator S. tridens and the spider Pedro-Neto et al., 2013), causing extensive damage to mite T. bastosi were obtained from experimental jatropha cultivated in several regions of Brazil (Santos jatropha plantations belonging to the Active Germplasm et al., 2010). The control of T. bastosi requires the use Bank of the Lauro Bezerra Station of the Pernambuco of synthetic acaricides that are not registered for the Agronomy Institute (IPA - Serra Talhada, Pernambuco crop (AGROFIT, 2018), and among other aspects, this State (PE), Brazil). approach can cause problems such as pesticide re- A morphological study of the male genitalia of speci- sistance in the target organisms, fruit residues and envi- mens was conducted to confirm the identity of Stethorus ronmental pollution (Watanabe et al., 1994; Escudero beetles. The males were dissected and compared to the and Ferragut, 2005). In this context, studies are being original description of S. tridens (Gordon, 1982) in the conducted on the natural enemies of tetranychid mites to Gordon and Chapin (1983) identification key. The male evaluate their potential for the biological control of this genitalia had a pair of lateral teeth and a triangular apex pest (Oliveira et al., 2007; Marques et al., 2015). on the basal lobe, diagnostic characters of this species. The Stethorini comprise beetles that specialize on T. bastosi colonies were kept in the laboratory on phytophagous mites. Among them, Stethorus tridens Gerbox® plates (11.0 × 11.0 × 3.0 cm) containing foam Gordon (Coleoptera Coccinellidae) is noteworthy and (3.0 cm thick) that were moistened with distilled water was recorded associated with T. bastosi on Solanaceae and covered with filter paper. A jack bean leaf, Ca- in North-East and South-East Brazil (Fiaboe et al., navalia ensiformes (L.) DC., was placed on the paper, 2007; Britto et al., 2009; Costa et al., 2017). and its borders were surrounded by moist cotton wool to Life table studies are fundamental for understanding prevent the mites from escaping (Reis and Alves, 1997). the population dynamics of a species since they provide The predators were reared in plastic pots (9 cm diame- a comprehensive view of its survival, development and ter) on T. bastosi infested jatropha leaves. Leaf petiole reproduction in certain environmental conditions (Cop- were kept in small tubes of water to maintain turgidity pel and Mertins, 1977). According to Bellows and Van (Costa et al., 2017); the leaves were changed every two days to maintain satisfactory densities of T. bastosi. The Results rearing units were maintained in air-conditioned cham- bers (27 ± 2 °C, 70 ± 10% RH and a 12-h photophase). Biology of S. tridens The jatropha plants used in the experiment were grown Data on the development of S. tridens (egg, four larval in 5-L pots containing soil, commercial substrate and instars, pupa and adult) are presented in table 1; there bovine manure at a 3:1:1 ratio, irrigated every 2 days, were no significant differences between males and fe- housed in 1.5 × 1.0-m cages coated with fabric and males. maintained in the experimental area. Newly deposited S. tridens eggs are bright, milky white and elongated, but the colour may gradually Biology change to orange during the incubation period. The eggs Thirty eggs of standardized age (up to 24 hours) were were individually deposited on leaf ribs and adhered obtained from the reared S. tridens females; each egg firmly to the leaf surface (figure 1 a-b). was placed in an individual plastic pot (9 cm diameter) The mean development time for S. tridens eggs was containing one T. bastosi-infested jatropha with the pet- 3.5 days, corroborating the observations by Fiaboe et al. iole in a tube containing water. (2007) on S. tridens fed with Tetranychus evansi Baker Observations were performed at 24-h intervals to de- et Pritchard (table 1). Four larval instars were observed termine the duration and survival of each of the devel- over a total of 5.9 days (table 1), which was consistent opment instars of S. tridens. When the insects reached with the observations by Hodek (1973) for most coc- adulthood, one adult male was added to each of the are- cinellid species. The larvae show blackish coloration nas containing females for mating, and when the male and numerous dark brown bristles along the dorsum, died, it was replaced by others until the female died. and all stages are similar. They are differentiated based The eggs laid by the females were raised separately to on the size of the cephalic capsule and the presence of the adult stage to determine the progeny sex-ratio. the exoskeleton (figure 1 c-d) (Khan et al., 2002). All tests were conducted in controlled growth cham- The 1st, 2nd and 3rd larval instar periods were short, bers at 27 ± 2 °C, 70 ± 10% RH and a 12-h photophase. during which the larvae actively searched for food. The The experiment was conducted in a completely random- development time of the 4th instars was longer, and ac- ized design with 30 replicates, and the data were sub- cording to Hodek (1973), this allows the individuals to jected to analysis of variance using the program Sisvar obtain the nutritive substances required for transfor- version 5.6 (Ferreira, 2011). mation into pupa and their later emergence as adults. As the 4th instar larvae matured, they reduced feeding activ- Fertility life table ity and moved little, becoming red and fixing to the sub- Life table parameters were determined from the sur- strate of the leaf by means of a viscous fluid to pupate. vival and fecundity data of S. tridens females, and the The pupal stage is one of the inactive phases in Coc- following development and survival parameters of the cinellidae. The pupa is reddish orange when newly juvenile and adult forms of the progeny were obtained transformed and becomes blackish, covered with nu- during the biological evaluation: intrinsic population merous bristles (Chazeau, 1985). They are attached by growth rate (rm); net reproduction rate (Ro); finite rate the abdomen to the leaf surface until they emerge as of population increase (λ); average generation time (T); adults (figure 1 e-f). In the present study, this period population doubling time (Td); specific fertility (mx); lasted an average of 2.95 days in both males and fe- and survival rate (lx). The biological parameters were males (table 1). calculated using the LIFETABLE.SAS tool developed Newly emerged adults had a reddish coloration that by Maia et al. (2000) in the "SAS System" environment gradually changed to black (figure 1 g-h). The duration of SAS software version 8.02 (SAS, 2001). of development from the egg to the adult stage lasted an Table 1. Duration (mean ± standard error) of the biological stages of S. tridens fed T. bastosi on J. curcas in the la- boratory. Development time (days) a Biological phase Survival (%) Females (n = 11) b Males (n = 9) Mean (n = 20) Egg 96 3.5 ± 1.0 3.6 ± 1.0 3.5 ± 1.0 Larval instars I 100 1.3 ± 1.1 1.3 ± 0.5 1.3 ± 0.47 II 100 1.2 ± 0.4 1.4 ± 0.7 1.3 ± 0.57 III 100 1.1 ± 0.3 1.0 ± 0.0 1.05 ± 0.22 IV 93 2.2 ± 0.4 2.3 ± 1.3 2.25 ± 0.97 Larval stage 5.7 ± 0.5 6.1 ± 0.6 5.9 ± 1.12 Pupal stage 89 3.0 ± 0.4 2.9 ± 0.3 2.95 ± 0.39 Egg - adult 93 12.2 ± 1.2 12.6 ± 1.3 12.35 ± 1.23 Longevity 57.9 ± 19.2 56.1 ± 14.4 57.1 ± 17.