Biological aspects of Harmonia axyridis in comparison with Cycloneda sanguinea and Hippodamia convergens

The objective of this work was to evaluate the development, survival, reproductive capacity, and longevity of the Asian ladybug Harmonia axyridis in comparison with Cycloneda sanguinea and Hippodamia convergens. Coccinellid larvae and adults were fed daily with Schizaphis graminum. Ten couples of each species were isolated for evaluation of the adult phase. The duration of the larval stage of H. axyridis is the longest (10.2 days) and its adults are the heaviest (29.7 mg) compared with C. sanguinea and H. convergens. The three species showed similar percentages of survival during the developmental stages. An average of 82% of C. sanguinea, H. axyridis, and H. convergens larvae reached adulthood, which indicates that temperature (25°C) and the offered prey are favorable to coccinellid development. Harmonia axyridis produces a higher total number of eggs per female (1,029.2) than the other evaluated species. However, H. axyridis, which lives for an average of 147.2 days, does not show a significantly greater longevity than C. sanguinea (87.2 days) and H. convergens (134.3 days).


Introduction
The Asian ladybug Harmonia axyridis (Pallas) is a notable polyphagous and effective predator (Almeida & Silva, 2002).However, the species is characterized as having a negative impact on the populations of other coccinellids, by displacing them through interspecific competition (Koch, 2003).
In Brazil, Milléo et al. (2008) observed that the population of H. axyridis increased, whereas those of other coccinellid species reduced in orchards with different types of fruit trees.In a secondary forest area with a predominance of ferns, Pinus sp. and Baccharis spp., Martins et al. (2009) reported low abundance of coccinellids, mainly Cycloneda sanguinea (Linnaeus) and Hippodamia convergens (Guérin-Meneville) after the introduction of H. axyridis.Berthiaume et al. (2007) studied the biology of H. axyridis in a coniferous forest in Canada, comparing it with that of the native species Anatis mali (Say).The authors found higher seasonal synchrony between the life cycles of A. mali and the aphid Mindarus abietinus (Koch) than between H. axyridis and M. abietinus.In spring, adults of A. mali colonized plants about two weeks earlier than exotic species, enabling their larvae to be present during the population peaks of aphid pests.Therefore, A. mali is better adapted than H. axyridis to the control M. abietinus.Lanzoni et al. (2004) compared the biological aspects of H. axyridis with those of the native coccinellids H. variegata (Goeze) and Adalia bipunctata (Linnaeus) and observed differences in the durations of the egg, larva, and pupa stages between these predators.Harmonia axyridis showed a longer larval period (10.4 days) than the other species.According to the authors, the biological traits of H. axyridis do not seem to contribute to its success as an invasive species.
These studies are essential in determining the population growth potential of the species because they consider the competitive capacity of its natural enemies (Lanzoni et al., 2004).However, no comparative biological studies among H. axyridis, H. convergens, and C. sanguinea, which are established species in Brazilian agroecosystems, have been conducted to date.
Because the records on the Asian ladybug in Brazil are relatively recent, information about its behavior, potential for predation, biology, food preference, and competition with other coccinellid species is limited.
The objective of this work was to evaluate the development, survival, reproductive capacity, and longevity of the Asian ladybug H. axyridis in comparison with C. sanguinea and H. convergens.
Larvae of each predator species were obtained by rearing coccinellids from the Laboratory of Insect Ecology according to Santos et al. (2009).The rearing of S. graminum began by using aphids collected from leaves of sorghum plants (S. bicolor) grown at the experimental area of FCAV/Unesp.The aphids were kept on 45 cm sections of sorghum stems of the BRS 310 cultivar -susceptible to attack by this hemipteran -, packed in glass containers with 300 mL of water, and sealed with PVC film.Water and stems were replaced weekly.
Newly hatched coccinellid larvae were individualized and fed daily, ad libitum, S. graminum nymphs and adults, and the treatments were represented by the ladybug species.Each experimental block consisted of a Petri dish of 9.0 cm in diameter, containing the predator species and prey.The insects were maintained in a climatic chamber at a constant temperature of 25±1.0°C,under a 12 hour photoperiod and 70±10% relative humidity.Thirty replicates per treatment were performed, and observations were made daily.The duration and viability of the instars were determined during the immature phase, including the pre-pupal phase in the fourth instar, the pupal phase, and the egg-adult period.The fresh mass of the coccinellids was obtained by weighing 15 larvae of each species, 24 hours after each instar change, 1 day after the emergence of adults.
For evaluations of the adult stage, individuals originated from the corresponding experiment with the immature stages of coccinellids were used.Ten couples of each species were isolated, each representing one replicate.These couples were kept in transparent 350 mL plastic cups and fed S. graminum daily.Observations were conducted daily, and the periods of pre-oviposition and oviposition, daily and total oviposition capacity, and longevity were determined.To determine the incubation period and egg viability of the species of coccinellids, laid eggs were separated daily for a period of seven days for each couple.The number of eggs in each laying was counted, and the number of eggs hatched and the time to hatching (in days) were assessed.
The experimental design was completely randomized.Data were subjected to analysis of variance (Anova), and the means were compared by the Tukey test, at 5% probability.Residue analysis was carried out to verify the assumptions of Anova.The SAS software, version 9.0 (SAS Institute, Cary, NC, USA), was used.

Results and Discussion
The duration of the developmental stages differed significantly among the three coccinellid species (Table 1).The period of egg incubation in H. axyridis and H. convergens was approximately 1.5 days shorter than in C. sanguinea.Conversely, with the exception of the second larval stage, H. axyridis and H. convergens showed a longer duration for the other phases of development than C. sanguinea.
The fourth-instar stage was longer in H. axyridis compared with the other evaluated species.According to Santa-Cecília et al. (2001), during the fourth instar, coccinellid larvae require higher amounts of nutrients for pupal development and differentiation into adults.This is also the instar in which the larvae have the greatest voracity, since, during this stage, individuals consume 60 to 80% of their total prey (Hodek & Honěk, 1996).For purposes of biological control of the aphid S. graminum, the extension of the fourth instar in the Asian species is advantageous because larvae at this stage may be equally or more voracious than adults and have the additional advantage of, once released, showing a reduced capacity for dispersion.Lanzoni et al. (2004) compared the development of H. axyridis, H. variegata (Goeze), and A. bipunctata (Coleoptera: Coccinellidae) fed with the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) and recorded a 1 day extension in the larval phase of H. axyridis in comparison with the other species.
In the present study, the duration of the larval phase was similar to that found by Michaud (2000) (9.0 days) and Lanzoni et al. (2004) (10.4 days) for H. axyridis fed with Toxoptera citricida (Kirkaldy) and M. persicae, respectively, and maintained under the same temperature conditions, i.e., 25°C (Table 1).However, the duration of the phases was longer in H. axyridis (14.0 days) when the species was subjected to a temperature of 30ºC and fed with Acyrthosiphon pisum (Harris) (Lamana & Miller, 1998).Because temperature increases usually result in a higher development rate in insects (Speight et al., 2008), the shorter developmental time observed for H. axyridis suggests that the aphid S. graminum was a favorable food for its growth.This highlights the nutritional quality of S. graminum as a prey for H. convergens and C. sanguinea, which completed the developmental phases in shorter times, 17.2 and 17.5 days, respectively, than when fed with nymphs of the aphid Cinara spp., at 25 o C (Cardoso & Lázzar, 2003).The duration of the immature phases of C. sanguinea was similar to that reported by Santos et al. (2003) (8.1 days), at 25 o C, using S. graminum as food.
The duration of larval development is unique in each coccinellid species; however, factors such as room temperature and quality and quantity of food strongly influence this variable (Nedvěd & Honěk, 2012).The reduction in the developmental period during the immature phase may represent a strategy for the species to remain in that particular phase for a short time, particularly when these are more vulnerable to predation than others, increasing their likelihood of survival.Therefore, because adults of C. sanguinea emerged earlier than those of H. axyridis and  ------------------------------------------------------------------------(day)-------------------------------------------------------------------------C No significant differences in coccinellid survival were observed during the development of the different phases (Table 2).The first instar of H. axyridis showed the highest susceptibility and lowest percentage of survival.Santos et al. (2009) also observed a similar trend, reporting a 73.3% survival during this instar when the species was fed with S. graminum.However, this biological characteristic of H. axyridis is compensated for by the higher average number of eggs produced per female when compared with the other species (Table 3).Cycloneda sanguinea and H. convergens showed the highest fragility during the second instar, as revealed by the lowest rate of survival for this phase.This reduction in survival is probably related to the fact that the larval stage is of short duration in these two species (approximately 1 day), leaving no time for the larvae to store nutrients that are essential for energy expenditure during ecdysis.Rapid development, therefore, becomes a burden, resulting in a reduction in survival.Both species showed significantly shorter durations in this phase in comparison with that observed for H. axyridis (Table 1).Approximately 74.3% of C. sanguinea, 82.9% of H. axyridis, and 88.6% of H. convergens larvae reached adulthood, indicating that the temperature and the prey provided were favorable for their development.
Reproductive parameters varied among the evaluated species (Table 3).Hippodamia convergens showed a shorter pre-oviposition period and a longer post-oviposition period than C. sanguinea and H. axyridis.The oviposition period in H. convergens was on average 116.2 days, which was longer than that observed for C. sanguinea, but similar to that of H. axyridis.
The highest fertility rates were observed in C. sanguinea and H. axyridis, which produced on average a total of 1,025.0eggs, twice the value for H. convergens females (Table 3).The number of eggs produced daily by C. sanguinea was three-fold higher than that observed for H. convergens and two-fold higher than that for H. axyridis.This characteristic allows C. sanguinea to produce a larger number of descendants within a shorter period than the other two studied species, resulting in a rapid population growth that may favor competition with H. axyridis and H. convergens for prey.However, H. axyridis females showed a distinct strategy by producing the highest total number of eggs compared with the other species.The higher oviposition capacity combined with egg viability, which is similar to that of the other evaluated coccinellids, comparatively favors an increase in Asian ladybug populations at each generation.This strategy has been shown to be efficient since, according to Martins et al. ( 2009), H. axyridis was dominant in the coccinellid community, representing 90% of the species sampled in Curitiba, state of Paraná, Brazil.Conversely, the most abundant species in 1999 and 2000, namely C. sanguinea and H. convergens, were affected by the introduction of exotic species, which represented less than 3% of the coccinellid community in 2006and 2007. Mignault et al. (2006) ) reported that H. axyridis produced three to five times more eggs than the coccinellids Propylaea quatuordecimpunctata L. and Coleomegilla maculata (De Geer) when fed with the soybean aphid Aphis glycines Matsumura, at 24 o C. According to Nedvěd & Honěk (2012), the number of eggs produced by Coccinellidae is characteristic of each species.This number increases with body size; however, it can also be influenced by
Means followed by equal letters, in the columns, do not differ by the Tukey test, at 5% probability.
Means followed by equal letters, in the columns, do not differ by the Tukey test, at 5% probability.