Note OVIPOSITION AND PREDATION OF Pentilia egena MULSANT ( COLEOPTERA : COCCINELLIDAE ) IN RESPONSE TO TEMPERATURE

The species Pentilia egena Mulsant is an important predator of armored scales that occur in citrus orchards in Brazil. To intensify this biological control, knowing bioecological aspects in necessary for the improvement of massal insect rearing. This research investigated the influence of temperature (19C, 24C and 29C) on the number of eggs laid by P. egena and the number of Aspidiotus nerii Bouché scales preyed by this coccinellid. The highest number of eggs laid and of scales preyed, 5.1 ± 0.59 and 11.3 ± 0.19, respectively, occurred at 29C. However, egg viability (52.86%) was reduced at this temperature, and was lower than those at 19C and 24C (78.10% and 74.07%, respectively). Temperature did not affect the ladybeetle oviposition behavior as the eggs were laid under the scale of preyed A. nerii.


INTRODUCTION
The coccinellids play an important role in biological insect control worldwide, as natural enemies of aphids, scales, mealybugs and mites (Hagen, 1962).The introduction of Rodolia cardinalis Mulsant from Australia to a number of countries to control the cottony cushion scale, Icerya purchasi Maskell, an important citrus pest, is a landmark for biological control and mass insect rearing (Caltagirone & Doutt, 1989).
The lady beetles are cosmopolitan insects and it is believed that there are ca.5,000 known species occur-ring in ecosystems as diverse as forest, "cerrado", tundra and agricultural crops.They are well adapted to most environmental conditions, behaving accordingly to the ecological niche they occupy (Olkowski et al., 1990;Iperti, 1999).
Among the Brazilian coccinellid species, Pentilia egena is one of the most important predators of citrus armored scales such as: Selenaspidus articulatus Morgan, Parlatoria pergandii Comstock, Parlatoria cinerea Deane & Hadden, Chrysomphalus aonidum L. and Unaspis citri Comstock (Gravena, 1986;Busoli, 1992).However, little is known about the preying behavior, the oviposition of P. egena, and the influ-Scientia Agricola, v.60, n.3, p.587-589, Jul./Sept.2003 ence of these factors on the population of its preys (Guerreiro, 2000).Data on development, reproduction and predation under several environmental conditions provide important resources for the evaluation of this predator in the field.The variation of temperature, for instance, is an extremely important factor to understand the ecology of this species, for it will act on the above described parameters, directly influencing the dynamics of the predator/prey ratio (Miller & Paustian 1992;Gyenge et al., 1998).
The consumption and ovipositon of coccinellids are closely related to the prey population density and to temperature (Hodek, 1967).Within a favorable limit of temperatures, the feeding ratio, the larval and adult development as well as the oviposition rate, have a considerable increase according to the increase in temperature (Hodek, 1973).
It is needless to point out the importance of determining the best thermal band for implementing coccinellid mass rearing programs, as well as to determine the effect of this parameter on the lady beetles under field conditions.Therefore, this research was carried out to evaluate the influence of temperature on the oviposition and preying behavior of P. egena on the armored scale Aspidiotus nerii reared on "cabotiá" pumpkins (Cucurbita maxima X Cucurbita moschata).

MATERIAL AND METHODS
Fifteen P. egena mated females were used per temperature treatment: 19 o C, 24 o C and 29 o C. The prey was the armored scale Aspidiotus nerii reared on "cabotiá" pumpkins (Cucurbita maxima X Cucurbita moschata) obtained from the rearing laboratory of UNESP, Jaboticabal, SP, Brazil.Each P. egena female was placed in a feeding and oviposition arena, consisting of a section of plastic tube (3 cm diameter x 3 cm high), one side closed with a piece of plastic foam and the other hold by pins on the surface of the pumpkin.Each arena contained ca.50 adult scales.The coccinellids were kept in the arenas for 24 hour and them transferred to other arenas.The armors of the preyed scales were counted and raised to look for eggs, which when found were transferred to Petri dishes and kept at the corresponding temperature for observing egg viability.The following biological parameters were evaluated: number of eggs layed and of scales preyed per day, egg viability and site preferred for oviposition.Data on oviposition and sites of oviposition were analyzed in a factorial design and means were compared by the Tukey test (P = 0.05).Analysis of variance was applied to the studies of preying capacity, and means compared by the Tukey test (P = 0.05) and egg viability compared by the χ-Square test (P = 0.01).

RESULTS AND DISCUSSION
The temperature did influence the preying behavior of P. egena.At 19 o C, 4.4 ± 0.56 scales were preyed per lady beetle, a value lower than that of 7.6 ± 0.46 scales per lady beetles obtained at 24 o C. The females kept at the highest temperature (29 o C) consumed 11.3 ± 0.19 scales per lady beetle, quite higher than the results obtained at the other temperatures.These results agree with those reported for the coccinellids Hippodamia convergens Guérin-Mèneville, Coccinella septempunctata L. and Coleomegilla maculata DeGeer (Shands & Simpson, 1972;Roach & Thomas, 1991).Extrapolating these results to field conditions, one should presume that preying efficiency would be higher in the seasons with daily temperatures between 25 o C and 30 o C.
Different temperatures did not affect the oviposition behavior of P. egena in relation to eggs laid under the scale of preyed A. nerii (Table 1).This is a characteristic behavior of the species to protect the progeny against predation, parasitism and climatic changes (Guerreiro et al., 2001).Total number of laid eggs (inside and outside the armor) was higher at 29 o C, but a decrease in egg viability (52.9%) was observed when compared to those obtained at 19 o C (78.1%) and 24 o C (74.1%).These observation are similar to those of Santos & Bueno (1993), who reported egg viability of Scymnus (Pullus) argentinicus Weise being higher at 20 o C, although the number of laid eggs had been lower.
The lowest egg viability at the highest temperature (29 o C) may be attributed to the egg dehydration, for most of them were wilted.Howe (1981)  Means followed by distinct capital letters in the column and small letters in the line differ by the Tukey test (P ≤ 0.05).Minimum significant difference (5%) temperature by oviposition local = 0,8494 and oviposition local by temperature = 0,7098

Table 1 -
Pentilia egena: number (mean ± s.e.) of eggs laid inside and outside of armor, and total.