Aqueous Extracts of Species of the Genus Campomanesia (Myrtaceae) Affect Biological Characteristics of Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae)

Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) is an insect pest that causes great damage to Brassica cultures. It is necessary to develop alternative control methods, because this pest is resistant to many synthetic insecticides that are harmful to the environment. The objective of this study was to evaluate the effects of aqueous extracts of Campomanesia adamantium, C. guazumifolia, and C. xanthocarpa on the life cycle of P. xylostella. These aqueous extracts were prepared in a concentration of 10 g/mL and then applied on cabbage disks of 4 cm2 to feed the larvae until they reached pupal stage. The disks were evaluated daily during the larval stage and replaced every 24 hours. The experiment consisted of ten replicates, each replicate containing five subsamples. The parameters evaluated were larval and pupal survival, pupal biomass, gender ratio, male and female longevity, number of eggs, fecundity, oviposition period and egg survival. The C. xanthocarpa extract increased larval stage and decreased pupal biomass and oviposition period. The C. adamantium extract decreased larval duration, pupal biomass, male longevity, and oviposition period. The C. guazumifolia extract decreased larval stage, male longevity, and oviposition period. The chemical composition of the extracts of Campomanesia species presented flavonoids such as quercetin, phenolic compounds, and tannins, and the highest retention time occurred in C. adamantium. Thus, the extracts of Campomanesia species were effective in decreasing and controlling the oviposition period of P. xylostella, probably because of the presence of flavonoids, which indicates a possible antioxidant potential and, therefore, the observed antibiosis.


Introduction
The diamondback moth, Plutella xylostella (Linnaeus 1758) (Lepidoptera: Plutellidae), is an important microlepidoptera for agriculture, being considered the main pest of Brassicaceae cultivations (Furlong et al., 2013). The highest loss caused by this insect refers to management costs, which amount to more than one billion dollars annually (Zalucki et al., 2012), resulting in vegetable damages of up to 100%, which makes them inappropriate.
The use of pesticides is still the method most used by producers to control insects that cause agricultural damage, such as P. xylostella. These pesticides are used because they are practical, fast, and efficient in population control (Talekar & Shelton, 1993), but their use may select for more resistant individuals (Thuler et al., 2007), which would probably maximize the problem. Therefore, it is necessary to seek control alternatives for these harmful insects. Some studies have shown that the use of insecticidal plants deserves to be highlighted because of their low toxicity, selectivity, and efficiency against numerous insect pests (Neves & Nogueira, 1996).
A recent study by Peres et al. (2017) shows evidence of the insecticide potential of Cerrado species. In this study, the aqueous extracts of three species were analyzed: Alibertia edulis (Rich.), Alibertia intermedia (Mart.), and Alibertia sessilis (Vell.) K. Schum. Treatments with A. intermedia and A. sessilis extracts resulted in the lowest oviposition period and number of hatched larvae. The harmful effects of these aqueous extracts on the life cycle of P. xylostella were attributed to flavonoids and other phenolic compounds present in A. intermedia and A. sessilis. According to the author, these aqueous botanical extracts have low toxicity when compared to synthetic insecticides and may be an effective approach to control P. xylostella populations.
The genus Campomanesia (Myrtaceae) is typical of the Cerrado and has been studied by several authors because of its anti-inflammatory (Silva et al., 2016a) and antioxidant (Abe et al., 2014) properties, leading us to hypothesize that this genus is potentially insecticidal, as the literature shows that the plant extract contains many chemical substances, such as flavonoids, tannins and saponins (Markman, 2002), resulting in antibiosis with insects. Plants have two types of metabolites: primary and secondary. Primary metabolites respond for plant survival, having an active function in the processes of photosynthesis, respiration, and nutrient assimilation, whereas secondary metabolites are closely associated with defense strategies (Nass, 2007).
The objective of this study was to evaluate the insecticidal activity of aqueous extracts of Campomanesia xanthocarpa O. Berg, C. guazumifolia (Cambess.) O. Berg and C. adamantium (Cambess.) O. Berg on the biological cycle of P. xylostella.

Rearing of Plutella xylostella
The larvae and pupae of P. xylostella used in the experiment were from Insect-Plant Interaction Laboratory of the Faculty of Biological and Environmental Sciences at the Federal University of Grande Dourados, Mato Grosso do Sul, Brazil. These stock creation is maintained under constant temperature conditions (25±2 °C) and relative humidity (55±5%).
Cabbage disks of 8 cm in diameter were used as oviposition substrate in wet filter paper disks. This set was changed daily. The adults were fed with diluted honey (10%). After oviposition, the discs with the postures were placed in a sterile, transparent plastic container measuring 30 cm long × 15 cm wide × 12 cm high. The container contained leaves of organic cabbage (B. oleracea var. Acephala) to feed larvae until they entered the pupal phase. The leaves were previously sanitized with 5% sodium hypochlorite solution and washed in running water. The pupae were placed in cages until the emergence of adults. The species were identified based on comparison with exsiccate specimens from the Universidade Federal da Grande Dourados (UFGD) herbarium. They are registered under the following numbers: Campomanesia adamantium, DDMS 5695; Campomanesia guazumifolia, DDMS 5254; and Campomanesia xanthocarpa, DDMS 4644.

Preparation of Aqueous Extracts
Aqueous extracts of C. adamantium, C. guazumifolia and C. xanthocarpa were prepared by maceration from leaves that were collected, dried in a forced circulation oven for 3 days at a maximum temperature of 40 °C (±1 °C) and then ground in a mill to obtain fine powder.   n the present st shows the effe nd mean numb on (Amoabeng ul, 2012), and  Vol. 11, No. 5; insects from plants, such as feeding inhibitors (Couto et al., 2016;Koul, 2005Koul, , 2008. In this line of study the genus Campomanesia interfered in the biological characteristics of P. xylostella. The increased duration of the larval stage induced by the extract of C. xanthocarpa is important for increasing the exposure time to natural enemies and the mean time of each generation, thus, decreasing overall population growth (Torres et al., 2001). Torres et al. (2006) corroborate that the duration of the larval stage is increased because of growth inhibitors or toxic substances present in the extracts.
The C. xanthocarpa extracts resulted in decreased larval and pupal survival and pupal duration, probably because the compounds present in the extracts act for longer in the middle intestine of P. xylostella. Among these compounds are some flavonoids such as quercetin, phenolic compounds, and tannins. The quercetin present in aqueous extracts of Campomanesia influences insect biology. Gazzoni et al. (1997) evaluated the effect of different quantities of rutin and quercetin on the biology of velvetbean caterpillars, Anticarsia gemmatalis (Lepidoptera: Noctuidae) and reported that both quercetin and rutin caused an increase in the number of days of the total cycle (third instar to adulthood) and gradually increased the mortality rate of caterpillars. Peres et al. (2017) verified that quercetin present in Alibertia sessilis and A. intermedia influences the biology of Plutella xylostella causing deformity. Silva et al. (2016b) verified that the rutin flavonoid negatively affected the biology of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) by prolonging the larval development time, reducing the weight of larvae and pupae and decreasing the viability of the pupae.
Another interesting feature is that the C. xanthocarpa extract increased larval duration, consequently increasing pupal biomass, whereas the C. adamantium extract decreased larval duration and pupal biomass. Therefore, pupal weight is directly related to the insect performance in the larval stage (Maroneze & Gallegos, 2009).
The extracts of C. adamantium and C. guazumifolia decreased the longevity of males in the couples evaluated, but the extract of C. xanthocarpa increased longevity by 13.4 days. There was no significant difference among treatments for females, except for C. xanthocarpa, which decreased longevity by 4.8 days.
There was no significant difference in number of eggs in all treatments, but there was a decrease in egg survival in the three Campomanesia extract treatments. However, C. xanthocarpa presented a better result, with only 26% of the total number of eggs hatching. This decrease may be related to the quantity and quality of nutrients absorbed during the larval stage, since these parameters may influence the number of ovarioles per ovary and consequently decrease egg production (Costa et al., 2004). This is very important in the field, because this decreased egg survival will decrease the number of individuals in the next generation, and fewer caterpillars will cause less damage to crops (Maroneze & Gallegos, 2009). According to Peres et al. (2017), the aqueous extract of Alibertia sessilis increased larval duration, which resulted in larval mortality or late pupal mortality.
In a recent study, Peres et al. (2017) reported that aqueous extracts of the genus Alibertia increase larval duration and decrease pupal duration, pupal biomass, and fecundity. The authors related these effects to the presence of the flavonoids rutin, quercetin, and luteolin.
Quercetin is present in species of Campomanesia and affects insect biology. Peres et al. (2017) reported morphological changes in the biology of P. xylostella when treated with aqueous extracts of A. sessilis and A. intermedia.
We concluded that all Campomanesia extracts tested resulted in modification of biological characteristics of P. xylostella, indicating effectiveness in controlling and decreasing future generations of this insect. Therefore, further studies on these species should be conducted, including a detailed isolation of substances and new tests using the extracts.