Exochomus Quadripustulatus Research Articles

Wax covers in larvae of two Scymnus species: do they enhance coccinellid larval survival?

We tested the protective function of larval wax covers in the two ladybird beetle species, Scymnus nigrinus and S. interruptus, against cannibalism, predation and ant aggression, and its importance for the distribution of both species in the field. Cannibalism was generally very low and not influenced by the presence or absence of the wax cover, or by larval size. Fourth-instar larvae of three ladybird species, Adalia bipuncata, Exochomus quadripustulatus and Harmonia quadripunctata, consumed Scymnus larvae-which are much smaller-regularly, independent of the presence or absence of waxes. By contrast, first-instar larvae of the three species had generally little success when attacking Scymnus spp. larvae. Wax-covered S. interruptus larvae survived significantly more attacks by the predacious carabid beetle Platynus dorsalis than larvae without wax cover. Wax-covered S. interruptus larvae and S. nigrinus larvae survived attacks by workers of the ant species, Lasius niger and Formica polyctena, respectively, significantly more often than larvae without wax covers. We show that, in the field, Scymnus larvae have higher densites in ant-attended resources than in unattended ones and conclude that both Scymnus species benefit from the ability to feed in ant-attended aphid colonies by a reduced predation risk.

Exochomine, a dimeric ladybird alkaloid, isolated from Exochomus quadripustulatus (coleoptera: coccinellidae).

Exochomine ( 5), a new dimeric alkaloid has been isolated from the European ladybird Exochomus quadripustulatus. Its structure and absolute configuration have been determined by single crystal X-ray diffraction analysis on the hydrochloride.

Structure of Ladybird (Coleoptera: Coccinellidae) Assemblages in Apple: Changes through Developmental Stages

Larvae, pupae, and adults of ladybird beetles were observed in an insecticide-free and an insecticide-treated block in an apple orchard near Budapest, Hungary during 1980–1982. Species numbers and densities in all developmental stages were higher and species turnover was lower in the insecticide-free block. Diversity and similarity indices showed more diverse and constant assemblages in the insecticide-free block. The adult assemblage was the most rich in species, with 19 species in the insecticide-free and 12 species in the treated block. The most common species overall were Coccinella septempunctata, Adonia variegata, Adalia bipunctata , and Exochomus quadripustulatus . The larval assemblage included nine and eight species for the untreated and treated blocks respectively, whereas the pupal assemblage had eight species in both blocks. Immature stages of 11 species were found in at least 1 yr and 10 of these was able to complete development in the orchard. The rate of success was higher in the insecticide-free block for most species. Only A. bipunctata reproduced successfully in both blocks in all three years but A. decempunctata and C. septempunctata were often successful.

Abnormal and variable sex ratios in population samples of ladybirds

While most ladybird species are believed to show a conventional 1:1 sex ratio, population samples from five different species of ladybird have been found to show significant excesses of females. The species involved are Anatis ocellata, Exochomus quadripustulatus, Chilocorus renipustulatus, C. bipustulatus and C. nigritus. All possess neo-XY sex chromosome systems. It is possible that the excesses of females reflect the recombination of segments present at the ends of the neo-XY sex bivalent. If the products of recombination are more lethal in males than females, differences in sex ratio will result. An alternative hypothesis involves an interaction between Y-linked factors and maternally inherited factors, possibly of a transposable element type. The maintenance of such excesses of females in several species, in different taxonomic groups within the Coccinellidae, and the presence of differences in different populations of one of the species, must reflect a selective advantage for these excesses in natural populations of these species.

A correlation between B chromosome frequency and sex ratio in Exochomus quadripustulatus

A survey of natural populations of the British ladybird Exochomus quadripustulatus revealed the presence of a single large, acrocentric, supernumerary (B) chromosome in all sites visited. Studies were confined to male meiosis, where more than one B was never found to accompany the six bivalents and neo-XY sex pair. The percentage of males possessing B chromosomes varied from 6.4% to 28.6% in 14 different populations. The sex ratios present in these populations also varied. In some equal numbers of males and females were present, in others there were significant excesses of females. A linear regression was found between the percentage of B chromosomes and the percentages of males and females in those populations. It is suggested that the B chromosomes are not in themselves responsible for the sex ratio differences found for similar differences in sex ratio have been found in related neo-XY species lacking B chromosomes. It is more likely that those factors affecting sex ratio are also responsible for affecting the frequencies of B chromosomes in different populations.