Courtship pheromone production and body size as correlates of larval diet in males of the arctiid moth,Utetheisa ornatrix

Abstract

Hydroxydanaidal, the corematal courtship pheromone of maleUtetheisa ornatrix, shows pronounced quantitative variation in natural populations of the moth. Males that, as larvae, fed on seed-bearing rather than immature food plants (Crotalaria spectabilis orC. mucronata) produce higher levels of hydroxydanaidal. Such males also have higher systemic loads of pyrrolizidine alkaloid, the known metabolic precursor of hydroxydanaidal, whichUtetheisa sequester from their larval diet and which is concentrated in the seeds ofCrotalaria. Males raised on seed-bearing plants also achieve higher adult weight. In the context of sexual selection, therefore, femaleUtetheisa could, through assessment of male hydroxydanaidal levels, gauge both the alkaloid content and body weight of their suitors.

Diet-Mediated Pheromones and Signature Mixtures Can Enforce Signal Reliability

“…Typically, such studies reveal an increase in total pheromone output or attractiveness in individuals given a high quality diet, but find no change to the relative proportions of chemical components present in the pheromone. For example, Conner et al, 1981Conner et al, , 1990 Species recognition male cockroaches, Nauphoeta cinerea, provided with a diet rich in carbohydrates were more attractive to females and had greater pheromone output for three active pheromonal components, but there were no significant difference in the relative proportion in each of these components (South et al, 2011). Such dietmediated chemical cues may provide the receiver with indirect information about the signaller's genotype or direct information about the signaller's reproductive potential through biological pathways and trade-offs.…”

“…Males of several species of Lepidoptera, including the butterflies Danaus chrysippus (Schneider et al, 1975), D. gilippus (Dussourd et al, 1989), Idea leuconoe (Nishida et al, 1996), and the moth Utetheisa ornatrix (Conner et al, 1981(Conner et al, , 1990, provide females with a defensive chemical during courtship. Males sequester a pyrrolizidine alkaloid from their host plant as an adult or during the larval stage, some of which is stored in somatic tissue, likely as a form of chemical defense, and some is chemically modified to the male sex pheromone (Schneider et al, 1975;Conner et al, 1981).…”

Chemical defense against predation in an insect egg

“…The other diet [(ϩ) diet], also based on pinto beans, contains a supplement of seeds of Crotalaria spectabilis, another foodplant of Utetheisa (1). Utetheisa reared on the (ϩ) diet contain monocrotaline, the principal alkaloid of C. spectabilis, in an amount (0.6 mg per adult) (10) commensurate with that of alkaloid in Utetheisa raised on C. spectabilis plants (0.7 mg per adult) (11). Utetheisa raised on (ϩ) diet produce eggs [(ϩ) eggs] containing in the order of 0.9 g monocrotaline per egg (12).…”

Sexually transmitted chemical defense in a moth (Utetheisa ornatrix)

“…Female Utetheisa themselves sequester PA as larvae so that at adult emergence they already contain a self-acquired quantity of the chemicals. However, that quantity is variable, and it can be low, as is the case when the larvae have access to the leaves of Crotalaria only, rather than to the PA-rich seeds as well (18). The male's PA gift is therefore to be viewed as an important supplement, which, during times of PAshortage in the female, could be the bonus that ''makes the difference.''…”