Pentatomid predators (Hemiptera: Pentatomidae) have been evaluated for the augmentative biological control of insect pests (Tipping et al. 1999), which necessitates the study of their biology to develop mass rearing methodologies (Zanuncio et al. 2001). The predator Podisus nigrispinus (Dallas, 1851) (Heteroptera: Pentatomidae) is common in the Americas and in several agroecosystems in Brazil where it is an important biological control agent of defoliating caterpillars and other insects (Molina-Rugama et al. 1997; Medeiros et al. 2003; Torres & Zanuncio 2001).

Podisus nigrispinus is polyandrous and its females perform up to 13 copulations with 3 to 4 males over a 1–2 wk period, which is sufficient to fertilize its eggs and to produce nymphs for over 80% of its lifetime (Torres & Zanuncio 2001). Costs and benefits of reproduction are asymmetric for males and females, resulting in sexual conflict (Watson et al. 1998). Mate choice can affect reproductive success and females may have multiple copulations to maximize their offspring (Ridley 1990). This behavior may increase female gains in genetic and nutritional material (Reynolds 1996) resulting in higher fertility and offspring heterogeneity (Koshiyama et al. 1996). Disadvantages to multiple mating include: 1) energy expenditure, 2) increased risk of predation (Crudgington & Siva-Jothy 2000); 3) contamination by pathogens (Rolff & Siva-Jothy 2002) and 4) toxic effects of substances transferred during ejaculation (Chapman et al. 1995).

Females of P. nigrispinus with several long copulations are more fecund (Torres & Zanuncio 2001; Sousa-Souto et al. 2006; Rodrigues et al. 2009), but consequences of multiple mating remain unclear. The objective of this research was to elucidate female preference for mates and to determine the consequences of these preferences.

MATERIALS AND METHODS

The experiment was conducted under laboratory conditions at the Laboratory of Biological Control of the Department of Animal Biology of the Federal University of Viçosa (UFV) in Viçosa, Minas Gerais State, Brazil in a climate chamber at 28 ± 1 °C, 70 ± 10% R.H. and 12:12 h L:D.

RESULTS

In the no-choice tests, the numbers of matings were similar for females mated with siblings or non-siblings males (Fig. 1A) (3.3 ± 1.36, and 1.7 ± 0.73 times, respectively; χ² = 2.0; P > 0.05).

The average oviposition period of a female mated both with a sibling + a non-sibling male was shorter (6–7 days) than the oviposition periods following a mating with either a sibling or a non- sibling male (16–16.5 days) (Fig. 1B). Number of eggs per female was the lowest when the female had mated with a sibling + a non-sibling male (choice) (Fig. 2A). However, numbers of eggs/ egg mass and of egg masses did not differ between females mated with siblings, non- siblings or with both types of males (Fig. 2B, C).

The average number of nymphs per female that had mated with a non-sibling male was the highest, the number of nymphs per female that had mated with a sibling were intermediate and the number of nymphs per female that had mated with both kinds of males produced the fewest nymphs (Fig. 3A). The type of male with which the female mated did not affect female longevity (Fig. 3B).

Fig. 1.

Number of matings (A) (ANOVA: F1; ₁₈ = 0.7458; P > 0.05) and oviposition periods (days) (B) (KruskalWallis test: KW = 8.2518; P < 0.05) of Podisus nigrispinus females each held either with a sibling, a non-sibling or both kinds of males in the laboratory at 28 ± 1 °C, 70 ± 10% RH and 12:12 h L:D. Bars on the columns represent standard errors. Abbreviations: S - sibling; N-S - non-sibling; and S + N-S - sibling plus non-sibling.

Fig. 2.

Number of eggs oviposited (A) (Kruskal-Wallis test: KW = 6.0351; P < 0.05); number of eggs/egg mass (B) (Kruskall-Wallis test: KW = 3.2535; P > 0.05); and number of egg masses (C) (Kruskal-Wallis test: KW = 1.9766; P > 0.05) per Podisus nigrispinus female held either with sibling, non- sibling or both kinds of males in the laboratory at 28 ± 1 °C, 70 ± 10% RH and 12:12 h L:D. Bars on the columns represent standard errors. Abbreviations: S - sibling; N-S - non-sibling; and S + N-S - sibling plus non-sibling.

Fig. 3.

Mean number of nymphs per egg mass (A) (Kruskal-Wallis test: KW = 6.1170;P < 0.05) and mean longevities (B) (Kruskal-Wallis test: KW = 1.0721; P > 0.05) of Podisus nigrispinus females each held either with a sibling, a non- sibling or both kinds males in the laboratory at 28 ± 1 °C, 70 ± 10% RH and 12:12 h L:D. Bars on columns represent standard errors. Abbreviations: S - sibling; N-S - non-sibling; and S + N-S - sibling plus non-sibling.

DISCUSSION

Females of P. nigrispinus did not discriminate between sibling and non- sibling males in the laboratory. This may lead to decline of fitness due to inbreeding as observed for many insect species (Henter 2003; Clutton-Brock 2007; Shuker 2010)

The shorter oviposition period of females in the choice-test may reflect conflict between males, because the number of copulations should have been adequate to fertilize most eggs produced (Torres & Zanuncio 2001). Quantity of sperm transferred during mating can be low and sperm competition high in polygamous insects, which can decrease oviposition periods (Parker et al. 1997; Arnqvist & Nilsson 2000; Elgar et al. 2003; Crudgington et al. 2010; Rodrigues et al. 2008).

The greater number of eggs laid and the higher egg viability of P. nigrispinus females mated with non-sibling males indicate that this predator can reduce inbreeding by mating with unrelated males. Inbreeding could be reduced or avoided in laboratory rearing facilities by keeping P. nigrispinus females separate from sibling males. Sexual conflict between males and females after mating is ubiquitous and increases competition between the first ones to fertilize eggs (Stockley 1997).

The similar longevities of females in the various treatments may indicate no differences in quantities of sperm and accessory substances transferred by P. nigrispinus males. The nutritional content of sperm of this stinkbug has been poorly studied, but males of other insects provide sperm rich in nutrients as a nuptial gift (Pivnick & McNeil 1987; Koshiyama et al. 1996; Smedley & Eisner 1996). Accessory substances are used in the processes of cellular respiration and vitellogenesis (Koshiyama et al. 1996), oviposition (Herndon & Wolfner 1995), sperm activation (Osanai & Chen 1993) and to maintain sperm viability during storage in the spermatheca (Tram & Wolfner 1999), all of which tend to increase female longevity.

The increased oviposition and egg viability rates for females that had mated with non-sibling males confirm the need of multiple mating for the reproductive success of this species (Torres & Zanuncio 2001). Podisus nigrispinus nymphs aggregate from the time of hatching until transformation into adults (Torres & Zanuncio 2001), which increases the chances of mating with siblings and inbreeding.

CONCLUSIONS

Females of P. nigrispinus did not discriminate between sibling or non- sibling males for mating, which can lead to genetic inbreeding. However, the greater number of eggs laid and the higher egg viability of P. nigrispinus females mated with non-sibling males indicate that this predator can reduce genetic inbreeding by mating with genetically unrelated males.