title: Appetite for self-destruction: suicidal biting as a nest defense strategy inTrigonastingless bees.
abstract: Self-sacrificial behavior represents an extreme and relatively uncommon form of altruism in worker insects. It can occur, however, when inclusive fitness benefits are high, such as when defending the nest. We studied nest defense behaviors in stingless bees, which live in eusocial colonies subject to predation. We introduced a target flag to nest entrances to elicit defensive responses and quantified four measures of defensivity in 12 stingless bee species in São Paulo State, Brazil. These included threeTrigonaspecies, which are locally known for their aggression. Species varied significantly in their attack probability (cross species range = 0-1,P< 0.001), attack latency (7.0-23.5 s,P= 0.002), biting duration of individual bees (3.5-508.7 s,P< 0.001), and number of attackers (1.0-10.8,P< 0.001). A "suicide" bioassay on the six most aggressive species determined the proportion of workers willing to suffer fatal damage rather than disengage from an intruder. All six species had at least some suicidal individuals (7-83 %,P< 0.001), reaching 83 % inTrigona hyalinata. Biting pain was positively correlated with an index of overall aggression (P= 0.002). Microscopic examination revealed that all threeTrigonaspecies had five sharp teeth per mandible, a possible defensive adaptation and cause of increased pain. Suicidal defense via biting is a new example of self-sacrificial altruism and has both parallels and differences with other self-sacrificial worker insects, such as the honey bee. Our results indicate that suicidal biting may be a widespread defense strategy in stingless bees, but it is not universal.
authors.affiliation: Laboratory of Apiculture and Social Insects, Department of Life Sciences, University of Sussex, Brighton, BN1 9QG UK.
authors.forename: Kyle
authors.initials: K
authors.lastname: Shackleton
authors.affiliation: Laboratory of Apiculture and Social Insects, Department of Life Sciences, University of Sussex, Brighton, BN1 9QG UK.
authors.forename: Hasan
authors.initials: H
authors.lastname: Al Toufailia
authors.affiliation: Laboratory of Apiculture and Social Insects, Department of Life Sciences, University of Sussex, Brighton, BN1 9QG UK.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Balfour
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, Ribeirão Preto, 14040-901 Brazil.
authors.forename: Fabio S
authors.initials: FS
authors.lastname: Nascimento
authors.affiliation: Departamento de Entomologia e Acarologia, Escola Superior de Agricultura "Luiz de Queiroz", Universidade de São Paulo, Av. Pádua Dias 11, Piracicaba, São Paulo 13418-900 Brazil.
authors.forename: Denise A
authors.initials: DA
authors.lastname: Alves
authors.affiliation: Laboratory of Apiculture and Social Insects, Department of Life Sciences, University of Sussex, Brighton, BN1 9QG UK.
authors.forename: Francis L W
authors.initials: FL
authors.lastname: Ratnieks
keywords: Colony defense; Nest guards; Self-destructive behavior; Self-sacrifice; Stingless bees; Trigona