OF Podisus distinctus ( HETEROPTERA : PENTATOMIDAE ) FED ON LARVA OF Bombyx mori

Biological control has been reducing the use of chemical products against insect pests, specially predatory Pentatomidae. Species of this group can present high variations in their life cycle as a result of their diet. Thus, the objective of this research was to study nymph development and reproduction of Podisus distinctus (Stäl, 1860) (Heteroptera: Pentatomidae) fed on Bombyx mori L., 1758 (Lepidoptera: Bombycidae) larvae (T1), compared to those fed on Tenebrio molitor L., 1758 (Coleoptera: Tenebrionidae) (T2) and Musca domestica L., 1758 (Diptera: Muscidae) larvae (T3) at a temperature of 25 ± 0.5C, relative humidity of 70 ± 2%, and photophase of 12 h. Predators fed on B. mori showed duration of the nymph phase (18.68 ± 1.02) similar to those fed on T. molitor (18.32 ± 1.49). Pre-oviposition and oviposition periods and number of egg masses, besides eggs and nymphs per female, were higher with B. mori (5.83 ± 2.02; 15.00 ± 7.40; 8.42 ± 1.84; 296.69 ± 154.75; and 228.55 ± 141.04, respectively) while longevity of males and females of P. distinctus was 25.76 ± 16.15 and 35.00 ± 16.15 days with T. molitor, and 20.57 ± 13.60 and 23.46 ± 12.35 days with B. mori, respectively.


INTRODUCTION
Biological control can reduce pest populations and maintain environmental balance without utilization or with lower insecticide use, which can improve life quality in different ecosystems (Symondson et al., 2002).
It is important to use alternative prey to replace natural ones with high nymph viability, and to produce heavier predator females for successful establishment under field conditions.For this reason, the objective of this research was to evaluate biological aspects of the predator P. distinctus fed larvae of B. mori, compared to those fed on larvae of T. molitor or M. domestica.

MATERIAL AND METHODS
This research was developed in the Laboratory of Biological Control of the Centro de Biotecnologia Aplicada à Agropecuária (BIOAGRO) of the Federal University of Viçosa (UFV) in the Municipality of Viçosa, State of Minas Gerais, Brazil.Research was done with a temperature of 25 ± 0.5 o C, relative humidity of 70 ± 2%, and photophase of 12 h.
Egg masses of P. distinctus were obtained from a mass-rearing facility of the Laboratory of Biological Control where this predator was fed larva or pupa of T. molitor.Egg masses were kept in Petri dishes (9.0 x 1.2 cm) with a cotton wad soaked with distilled water until nymph emergence.Nymphs of P. distinctus were individualized in Petri dishes of similar size at the beginning of the second instar until emergence of adults, when they were sexed by the external appearance of their reproductive organs and conditioned in 500 ml plastic pots.Females of P. distinctus were mated three days after emergence with males of similar age, and pairs of this predator were maintained in these pots until their death.Nymphs and adults of this predator received one of the alternative preys in treatments T1(larvae of B. mori); T2 (pupae of T. molitor); and T3 (larvae or pupae of M. domestica).These treatments had seven, seven, and five replications, each one represented by two 500 ml pots with a pair of P. distinctus for treatments T1, T2, and T3, respectively.
Survival and duration of each instar, numbers of egg masses, of eggs and nymphs per female, periods of pre-oviposition, oviposition, and posoviposition, besides longevity and weight of adults of P. distinctus 24 h after their emergence, were daily observed.Results were submitted to a variance analysis according to a complete randomized design and means were compared with the test of Duncan at 5% probability level.
Survival of P. distinctus was 100% in the first instar when this predator did not feed on prey, while it was 91.66 ± 27.87%, 90.00 ± 30.25%, and 85.00 ± 36.00 in treatments T1, T2, and T3 during second instar with similar results between treatments.Survival during third instar was higher in T1 (96.36 ± 18.89) than in T2 (87.03 ± 33.90) and T3 (80.39 ± 40.09), while this period was similar between treatments in the fourth and fifth instars (Table 2).

DISCUSSION
Duration of the nymph phase of P. distinctus was longer with B. mori than with T. molitor and M. domestica, and that of fourth instar was also longer with this prey, which can be related to its poor quality.This shows that P. distinctus needs a longer nymph period to develop its reproductive organs to develop when fed poor-quality prey such as M. domestica (Zanuncio et al., 1998).Moreover, predatory Asopinae (Heteroptera) fed with betterquality food are heavier with higher reproduction, fecundity, and number of eggs and nymphs (Evans, 1982;Zanuncio et al., 1996).Other species of this group showed similar necessities because the nymph period of P. distinctus was also shorter when this predator was fed B. mori.This agrees with results for the predators Podisus sculptus (Distant) (Heteroptera: Pentatomidae) (Nascimento et al., 1997) and P. nigrispinus, with longer duration of the nymph phase with M. domestica (Zanuncio et al., 1996(Zanuncio et al., /1997))  and T3 (60.00 ± 49.60%).This survival was higher with T. molitor and lower with M. domestica than that reported by Zanuncio et al. (1998) for this predator.This can be due to an adaptation process of P. distinctus after several generations in the laboratory.
The pre-oviposition period of P. distinctus was shorter in treatment T1 which shows that B. mori is a better quality prey; it also indicates that females of predators can more rapidly obtain nutrients for egg production with this prey than with T. molitor (Jusselino Filho et al., 2001).Moreover, oviposition and post-oviposition periods were longer when this predator was fed B. mori, further evidencing the quality of this prey, as does higher reproductive capacity of P. distinctus, in a manner similar to that reported for Podisus maculiventris (Say, 1831) (Heteroptera: Pentatomidae) (O 'Neil & Wiedenmann, 1990).
Longevity of P. distinctus females was similar with B. mori, T. molitor, and M. domestica, suggesting that this generalist predator can maintain its longevity with different prey, and agreeing with reports of Zanuncio et al. (1997), but with reduced egg and nymph production which can limit the establishment. of P. distinctus in the field.
B. mori should be used when a higher number of individuals specially in mass-rearing programs of P. distinctus is necessary because this predator showed a higher number of eggs and nymphs and better nymph viability with this prey.However, the high costs of rearing B. mori, including the necessity of maintaining a mulberry crop and more specialized work, as well as coping with deficiency of leaves of this plant between crops, restricts the use of this prey to only when necessary in order to maintain a colony of this predator in the laboratory (Zanuncio et al., 1996(Zanuncio et al., /1997;;Zanuncio et al., 1998;Oliveira et al., 1999).Although it is possible to maintain P. distinctus with M. domestica larva, the use of this prey is not recommended due to consequent low egg and nymph production, as well as survival of this predator.For these reasons the colonies of P. distinctus should be reared with T. molitor pupae in laboratory.
Means followed by the same letter in a row do not differ from each other at 5% probability level by Duncan's multiple range test.
Means followed by the same letter in a row do not differ from each other at 5% probability level by Duncan's multiple range test.