Avaliação da seletividade dos extratos aquosos de algarobeira e de juazeiro sobre o predador Stethorus tridens (Coleoptera: Coccinellidae) em pinhão-manso

Abstract

The ladybugs belonging to the genus Stethorus (Coleoptera: Coccinellidae), stand out for being within the main groups of natural enemies used in biological control, as well as in Integrated Pest Management (MIP). Many species, such as S. gilvifrons, S. punctillum and S. tridens, have been studied and used in the control of pest mites in different regions of the world, as they present specificity in the predation of phytophagous mites, having preference for mites of the family Tetranychidae, the which have a high infestation power, causing damage to the host plant, such as yellowing of the leaves, reducing the photosynthetic rate, leading to the death of the plant. Currently, there is a great interest in seeking alternative methods that minimize or replace the use of synthetic insecticides / acaricides, such as the use of plant extracts. Therefore, the objective was to evaluate the selectivity of aqueous extracts of algarobeira and juazeiro over the predator S. tridens, aiming at the use of the two associated methods (Biological Control + Plant Extracts). The study was developed at the Arthropod Ecology Center (NEA), at the Universidade Federal Rural de Pernambuco, Unidade Acadêmica de Serra Talhada (UFRPE-UAST). The experiments were conducted in a completely randomized design, with treatments: T1 = CL50 of the algarobeira extract; T2 = CL90 of the mesquite extract; T3 = LC50 of juazeiro extract; T4 = CL90 of juazeiro extract; T5 = distilled water (control). HPLC chromatography of lethal concentrations of algarobeira extracts (CL50 = 53.54% and CL90 = 85.35%), and juazeiro (CL50 = 53.54% and CL90 = 85.35%) was performed. The effects of the LC50 and the LC90 of the extracts on the survival of larvae, pupae and adults of S. tridens were evaluated, as well as the ovicidal effect and viability of the larvae from the eggs that were exposed to the concentrations; the rate of predation and the effect of repellency in larvae and adults of the ladybug. To evaluate the effect of the extracts on the survival of larvae, pupae and adults of S. tridens, they were mounted on 9 cm Petri dishes containing moistened cotton wool, filter paper and a disk of physic nut leaf. 10 individuals were placed in each arena. For the curative test the treatments were sprayed directly on the individuals and for the preventive test, the physic nut leaves were dipped for five seconds in each treatment and after 30 minutes the larvae and adults were released in each arena. Counting was done every 24 hours for 7 days. For the ovicidal test, adult females of S. tridens were removed from the breeding so that they could oviposit. After 24 hours the females were removed and the eggs individualized. The application of treatments in the curative and preventive test was developed following the methodology mentioned above. For the viability of the larvae, the survival of the larvae that hatched from the eggs exposed to the concentrations was checked for seven days, with the number of live / dead individuals being recorded every 24 hours. To assess the predatory capacity of S. tridens, arenas of physic nut leaves were infested with 100 individuals of T. bastosi and sprayed with the concentrations of the extracts, according to the treatments, for the curative test and for the preventive treatment. Jatropha discs were dipped for five seconds and then infested. Then, in each arena a female of S. tridens was released. After 24 hours and 48 hours of setting up the experiments, the predated mites / treatment will be counted. The repellent effect of the extracts on S. tridens larvae was evaluated in arenas of leaf discs of the physic nut inside Petri dishes. For each leaf disc, based on the central rib of the leaves, extracts were applied to only one half of the disc, according to the treatments. Then, in each arena, 10 larvae (L3 and L4) were released in the central rib. The arenas were covered with organza fabric and the counting took place after 30 minutes, 12, 24, 36 and 48 hours after application, without counting the side on which the larvae were (treated and untreated). For the purpose of repellency in adults, three plastic pots with a capacity of 100 mL were connected. In the central pot, 10 adult ladybugs were released and in the other pots, Jatropha leaves infested with mites were placed, and the treatments were then applied to one of the poles. After 48 hours, the number of individuals in each pot was counted. All experiments were maintained in B.O.D.-type climatic chambers, at a temperature of 27 ± 2 ºC, 70% ± 5 RH and 12 h of photophase, with 10 repetitions. All data were submitted to ANOVA and subsequently to regression analysis and comparison of means by the Tukey test at 5% probability. It was verified that the concentrations of algarobeira extract for the curative test did not affect the survival of the larvae (LC50 = 66.67% and LC90 = 55.56%), pupae (LC50 = 100% and LC90 = 100%), and adults (LC50 = 100% and LC90 = 100%), but the LC90 of the juazeiro extract showed an adult survival rate of 19.44%. There was no difference between the curative and preventive tests for the survival rate of larvae, pupae and adults. There was no ovicidal effect in any of the concentrations of the extracts in the two types of test. The viability of the larvae was affected only by the concentrations of the mesquite extract by the curative test (LC50 = 30.56% and LC90 = 36.11). The predation rate was affected by the CL90 of the extracts in the two types of curative test (EA-CL50 = 39.2% and EA-CL90 = 20.5; EJ-CL50 = 23.3 and EJ-CL90 = 18.1%) and preventive (EA-CL50 = 37.2% and EA-CL90 = 25.2; EJ-CL50 = 21.8 and EJ-CL90 = 14.6%). The CL90 of the two extracts showed repellency in S. tridens larvae with IS <1. It was found that only the CL90 of the algarobeira extract proved repellency in adults (IS = 0.108). In general, the algarobeira extract was more selective to S. tridens than the juazeiro extract. In this sense, studies of this nature should be encouraged, to assess the feasibility of associating the use of plant extracts with biological control using S. tridens in different agricultural systems.