Appetite for self-destruction: suicidal biting as a nest defense strategy in Trigona stingless bees

• Published in: Behavioral ecology and sociobiology Vol. 69; no. 2; pp. 273 - 281
• Main Authors: Shackleton, Kyle, Toufailia, Hasan Al, Balfour, Nicholas J., Nascimento, Fabio S., Alves, Denise A., Ratnieks, Francis L. W.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer 01.02.2015; Springer Berlin Heidelberg; Springer Nature B.V
• Subjects: aggression; altruism; Animal behavior; Animal Ecology; Apis mellifera; appetite; Bees; Behavioral biology; Behavioral Sciences; Bioassays; Biomedical and Life Sciences; Brazil; correlation; defensive behavior; Insects; Life Sciences; nesting; nests; Original Paper; Pain; predation; probability; stingless bees; Suicide; Teeth; Trigona; worker insects; Zoology; Brazil; Nest guards; Stingless bees; Colony defense; Self-destructive behavior; Self-sacrifice; Trigona
• ISSN: 0340-5443; 1432-0762
• DOI: 10.1007/s00265-014-1840-6

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 Sao Paulo State, Brazil. These included three Trigona species, 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 % in Trigona hyalinata. Biting pain was positively correlated with an index of overall aggression (P=0.002). Microscopic examination revealed that all three Trigona species had five sharp teeth per mandible, a possible defensive adaptation and cause of increased pain. Suicidal defense via biting is a new example of selfsacrificial 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.