Nutrients obtained during the larval period can be sufficient for reproduction, but adult feeding may be necessary to reproductive maturity and ripening of eggs. Adult food requirements of Thyrinteina arnobia (Stoll) (Lepidoptera: Geometridae), the main defoliator of eucalyptus in Brazil, may present problems in the laboratory. The fecundity and longevity of T. arnobia adults fed on 15% honey solution were evaluated. This solution did not improve the reproductive capacity and longevity of T. arnobia females but it favors those of males, which could increase mating probability. This is important because T. arnobia males emerge sooner than females, and feeding them could increase their longevity and chances of mating various females.
Geometridae larvae feeding on plants may become pests in cultivated forests (Swank et al. 1981). Thyrinteina arnobia (Stoll, 1782) (Lepidoptera: Geometridae) defoliates native Myrtaceae and it has been reported in eucalypt plantations with population outbreaks as the most important defoliator of this culture in Brazil (Bernardino et al. 2007; Zanuncio et al. 2003). The integrated management of this pest includes use of insecticides. (Oliveira et al. 2011), predators (Holtz et al. 2006; Zanuncio et al. 2006) and parasitoids (Menezes et al. 2012; Pereira et al. 2008a, 2008b).
Nutrition of adults of holometabolous insects is complex (Romeis & Wäckers 2002; Shirai 2006; Geister et al. 2008) because they depend, primarily, on nutrients accumulated during the larval stage (O'Brien et al 2002; Jervis & Boggs 2005), and food supplements for adults (Bauerfeind & Fischer 2005, 2009; Kehl & Fischer 2012; Milano et al. 2010).
Adult geometrid moths usually have a functional proboscis, and it is likely that most tropical species rely on flower nectar as their food source, although evidence is scarce (Axmacher et al. 2009).
Nutrition during the adult stage can affect the insect life cycle including longevity, preoviposition period and fecundity (Wackers et al. 2007). Sugar is important for reproduction (Watanabe 1992; O'Brien et al. 2004; Fischer & Fiedler 2001) and longevity (Carroll & Quiring 1992) of adult Lepidoptera. Most species of this order feed during adult stage on carbohydraterich diet (Romeis & Wackers 2000) what generally increases longevity and fecundity (Leather 1995).
Floral nectar is a source of food containing different types of sugars such as sucrose and fructose and glucose, and other nutrients such as amino acids (Romeis & Wackers 2000). Lepidoptera males and females can present different foraging strategies. Thus males feed on flowers with high sugar levels, while females may feed on flowers with high proportions of glucose and amino acids (Rusterholz & Erhardt 2000). These nutrients, which are important for the production of eggs, are also found in honey.
Thyrinteina arnobia adults are fed honey in the laboratory (Oliveira et al. 2005; Batista-Pereira et al. 2004) but their real need of this food is not clear. The objective was to study the effect of honey feeding by adults on reproduction and longevity of T. arnobia to improve its mass rearing.
Materials and Methods
Adults T. arnobia were obtained from a rearing facility of the Laboratory of Biological Control (LBCI) of the Federal University of Viçosa (UFV) in Viçosa, Minas Gerais State, Brazil. Larvae of this species were reared for one generation on Psidium guajava L.(Myrtales: Myrtaceae) plants in the field until the pupal stage and then transferred to the laboratory where they were maintained at 25 ± 2 °C and 70 ± 8% RH until they reached adult stage. Newly emerged T. arnobia adults were separated into pairs in 500 mL plastic vials, covered with a perforated lid for mating and oviposition at 22.39 ± 1.38 °C and 82.35 ± 6.56% RH. A 15% honey solution was supplied on cotton balls and changed daily. The pots with T. arnobia pairs were held in an open area near the LCBI in shelves until their death.
Reproductive capacities and longevities of Thyrinteina arnobia (Lepidoptera: Geometridae) either fed 15% honey solution or not fed. They were held at 22.39 ± 1.48 °C and 82.35 ± 6.56% RH.
Treatments consisted of 32 pairs of T. arnobia fed with 15% honey solution, and 30 unfed pairs. Each pair was a replication.
Egg masses of T. arnobia were collected and maintained at 25.0 ± 2.0 °C, 70 ± 8% RH and 12 h photophase until they had hatched. The preoviposition, oviposition and post-oviposition periods, and the numbers of egg masses and eggs per female, longevities of males and females and egg viabilities of T. arnobia were evaluated daily. Egg maases of females with more than one egg mass were used to evaluate egg viability; and the viabilities of first and last egg masses were evaluated. Data were subjected to the Wilcoxon test at the 5% probability level.
The mean preoviposition period of T. arnobia was similar between treatments with 2.06 days for females fed on honey solution and 1.9 days for non fed ones (P < 0.05) (Table 1).
The mean numbers of eggs and egg masses per T. arnobia female (Table 1) were, respectively, 1,173.2 eggs and 3.0 egg masses (fed ) and 1,140.0 eggs and 3.4 egg masses (unfed ), and with viabilities and incubation periods of 85.8% (fed) and 78.5% (unfed) and 9.1 days (fed ) and 9.2 days (unfed), respectively. These differences between the 2 treatments were not significant. In both treatments the first egg mass to be deposited by a female had about 3-fold more eggs than the second egg mass, and all subsequent egg masses had even fewer eggs that the second egg mass (Fig. 1). Egg viabilities were 82.43% for the first egg mass and 74.57% for the last one in the honey-fed treatment, and 78.58% for the first egg mass and 66.26% for the last egg mass in the unfed treatment; and the Wilcoxon test values of both treatmenst were similar values by (P < 0,05).
However the longevity of the honey-fed T. arnobia males (9.6 days) was longer than of unfed males (7.3 days) (P < 0.05) (Table 1). Honey-fed males showed 100% survival until the fifth day, compared to only 45% of unfed males. Few unfed males survived until the twelfth day, but 20% of honey-fed males survived for that period (Fig. 2A).
The longevity of honey-fed T. arnobia females was 9.3 days compared to 10.07 days for the unfed ones; thus these longevities were similar values between treatments (Table 1). The survival curves of honey-fed and unfed females were similar and both decreased continuously with time (Fig. 2B).
The honet diet of the adults had definite effect on reproduction, but not on the pre-oviposition periods of fed vs. unfed females. This indicates that T. arnobia females do not need feeding to initiate oviposition. This is similar to that reported for Pseudaletia sequax (Franclemont, 1951) (Lepidoptera: Noctuidae) whose pre-oviposition did not differ when receiving water or different carboidrates (Marchioro & Foerster 2012). This is not uncommon, and many lepidoptera species need no food during pre-oviposition because the females use the reserves they retained from the larval stage to produce eggs (Wheeler et al. 2000).
In both treatments the T. arnobia females when 2 days old laid most of their eggs in the first egg mass; and because the few number of eggs/eggmass in egg masses #3 to #6, the longevity of the females did not greatly affect the number of eggs that they lay. Thyrinteina arnobia does not need to feed in the adult stage. Likewise Diatraea sacharalis (Fabricius 1794) (Lepidoptera: Crambidae) adult females have no need, and their fecundities are similar are increased by being fed honey, sucrose, glucose in comparison to no food (Parra et al. 1999). Some lepidoptera adults can obtain carbohydrates and proteins from nectar, which are also important for egg production (Telang et al. 2001).
Feeding during the adult stage increased longevity of T. arnobia males. The same result had been found for Spoladea recurvalis (Fabricius, 1775) (Lepidoptera: Pyralidae) males fed a honey solution, which increased their speed and duration of flight compared to those receiving only water (Shirai 2006). This indicates the importance of feeding males that emerge sooner than the females. This occurs in the case of T. arnobia because the males have one instar less than the females. Thus, feeding may increase flight capacity of males, their capacity to find females and their mating probability. Moreover, male feeding is important because males can transfer nutrients to females in the spermatophore during mating (Watanabe & Hirota 1999).
Therefore, the similararity of longevity of the T. arnobia females between the 2 treatments may be attributed to the nutrients accumulated during the larva stage. This shows that appropriate food is citically more important for female than male T. arnobia larvae, In addition, in other lepidopterans, nutrients accumulated during the larval stage are known to supply adults with energy and nutrients to lay eggs (Awmack & Leather 2002). Besides, the importance of food to the youngest instars of T. arnobia is evident from their preferences between eucalyptus species depending on the instar and the age of the leaves (Lemos et al. 1999). Larval development in T. arnobia depends on the diet, which subsequently affects the reproduction and calling behavior of the female (Batista-Pereira et al. 2004). Adults of other lepidopteran species may need richer carbohydrate diets for reproduction and survival (Bauerfeind & Fischer 2005). Besides in some species, supplemental sugar feeding may increase of lifetime fecundity by 10-fold (Wackers et al. 2007).
Supplemental feeding of T. arnobia males on a honey solution is important to increase their longevity and to increase their capacity to finding females over a longer period of time. Moreover, T. arnobia adult females did not need supplemental feeding as adults, because they have a sufficient reserve of nutrients from the larva stage to enable them to reproduce. In addition, since T. arnobia females lay most of their eggs in the first egg mass, the prologation of their longevity does not result in many more progeny.
To “Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)” and “Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)”.