Morphological and biological characterization of a light-colored mutant in the multicolored Asian lady beetle, Harmonia axyridis

Abstract

Insect cuticle color formed with melanin pigments has numerous types of mutants which usually cause pleiotropic effects. Melanism has been widely studied, but mutants with light-colored phenotype as well as the consequent fitness changes have rarely been reported.Here, in the laboratory strain of Harmonia axyridis, we found a novel mutant gr and confirmed that the mutation was inherited in a simple Mendelian autosomal recessive manner. This mutant (HAM) continuously displayed a light-colored pigmentation versus dark blackish in the wild phenotype (HAW). L-DOPA and dopamine are melanin precursors, and less L-DOPA was present in the cuticle of larval and adult HAM mutants compared to HAW wild type, but more dopamine was detected in the larval cuticle of HAM (p ≤ 0.0235). For the orange background of elytra, the composition as well as total concentration of carotenoids was different between HAM and HAW, which resulted in significantly lower saturation value but significantly higher hue value in HAM than in HAW (p < 0.0001).Extensive fitness changes were detected in HAM. (a) HAM larvae had similar predation capacity and preimaginal development time as HAW, but the newly emerged adults were much smaller (p < 0.0001). (b) Both fecundity and egg hatch rate in cross ♀(HAM) × ♂(HAM) were significantly lower than those in ♀(HAW) × ♂(HAW) (p ≤ 0.0087), but were not different with those in ♀(HAW) × ♂(HAM).

Keywords: Harmonia axyridis; body color; fitness; melanin; mutant; pleiotropy.

Figure 1

The typical morphology of different stages of Hamonia axyridis mutant type (HAM) and wild type (HAW). Photographs were the dorsal view and taken under the same conditions

Figure 2

The concentration of L‐DOPA and dopamine in the cuticle of fourth instar larvae (a) and newly emerged female adults (b) of Harmonia axyridis mutant type (HAM) and wild type (HAW). Asterisk represents a significant difference between HAM and HAW (p < 0.05, independent sample t test)

Figure 3

The concentration of carotenoids in the elytra of newly emerged adults of Harmonia axyridis mutant type (HAM) and wild type (HAW). For both female and male, asterisk represents a significant difference between HAM and HAW (p < 0.05, independent sample t test)

Figure 4

Reproductive capabilities of different crossing combinations of Hamonia axyridis mutant type (HAM) and wild type (HAW). Average number of egg production and hatch rate were recorded for 15 days from first oviposition. Different letters represent significant differences among the crosses (lowercase and uppercase letters were used for egg production and hatch rate, respectively) (p < 0.05, Tukey's HSD test)

Figure 5

Resistance of Harmonia axyridis mutant (HAM) and wild type (HAW) to desiccation and ultraviolet (UVA) irradiation. (a) Weight loss of the fourth instar larvae after being restricted in extreme drought conditions for 36 hr; (b) Survival rate of 21st instar larvae after being exposed to UVA irradiation (365 nm) for 2 hr and then reared on Myzus persicae for 24 hr. Different letters represent significant differences between control and treatment (lowercase and uppercase letters were used for HAM and HAW, respectively) (p < 0.05, Tukey's HSD test)