B. K. Agarwala

Ladybird-induced life–history changes in aphids

Predator–mediated plasticity in the morphology, life history and behaviour of prey organisms has been widely reported in freshwater ecosystems. Although clearly adaptive, similar responses have only recently been reported for terrestrial organisms. This is surprising as aphids are polyphenic and develop very rapidly compared with their predators and often produce very large colonies, which are attractive to predators. Therefore, one might expect terrestrial organisms like aphids to show a facultative change in their development in response to the presence of predators and other results have confirmed this. The results presented below indicate that the pea aphid responded to the tracks left by ladybird larvae by producing a greater proportion of winged offspring, which avoid the impending increased risk of predation by dispersing. Associated with this was a short–term increase in activity and reduction in fecundity. The black bean and vetch aphids, which are afforded some protection from ladybirds because they are ant attended and/or unpalatable, did not respond in this way to the presence of ladybird larvae.

Effect of conspecific and heterospecific feces on foraging and oviposition of two predatory ladybirds: Role of fecal cues in predator avoidance

Growing evidence suggests a flow of chemical information from higher to lower trophic levels that affects foraging and oviposition of ‘prey’ in response to potential risks from predators. This was investigated in two species of ladybird predators of aphids, Harmonia axyridis and Propylea japonica. H. axyridis is known to be the stronger intraguild predator and P. japonica to be the more frequent intraguild prey in interactions of these two species. These ladybirds share aphid prey on mugworts, hibiscus, and Italian ryegrasses in fields of northern Japan but largely avoid each other on the same plant. Fecal cues of these ladybird predators were found to contribute in their assessment of predation risk from conspecific and heterospecific competitors in common habitats. Gravid females of H. axyridis reduced rates of feeding and oviposition when exposed to feces of conspecifics, but not when exposed to feces of P. japonica. In contrast, gravid females of P. japonica reduced feeding and oviposition when exposed to feces of both H. axyridis and its own species. Females of both ladybird species exhibited similar behavior in response to water extracts of feces. For P. japonica, the influence of heterospecific feces was greater than that of conspecific feces. Our results demonstrate that feces of ladybirds contain odors that have the potential to deter the feeding and oviposition activities of conspecific as well as heterospecific ladybirds. Such deterrence allows these insects to avoid predation risk. Differences in responses of the two predators are discussed.

Who eats whose eggs? Intra- versus inter-specific interactions in starving ladybird beetles predaceous on aphids

Starving adult beetles of Menochilus sexmaculatus and Coccinella transversalis resorted to intra- and inter-specific predation in the absence of aphid prey. Particularly at high egg densities, predators consumed eggs of their own species much more readily than eggs of the other species. Between the two ladybird species, the eggs of the smaller species, M. sexmaculatus, were less vulnerable to predation from the larger species, C. transversalis than vice versa. Results further indicate that adult female beetles are capable of discriminating eggs of their own species versus eggs of alien species on physical contact. The adaptive significance of this is discussed.

Effects of conspecific and heterospecific competitors on feeding and oviposition of a predatory ladybird: a laboratory study

Abstract There are several examples of intraguild interactions among insect predators of aphids, but little is known regarding the effects of interactions on feeding and oviposition of individual competitors in a guild. In the laboratory, we determined the feeding and oviposition responses of a ladybird predator to its conspecific and heterospecific competitors in an aphidophagous guild. Gravid females of Menochilus sexmaculatus (Fabricius) (Coleoptera, Coccinellidae) reduced oviposition, but not feeding, when exposed to immobilised conspecific or Coccinella transversalis (Fabricius) (Coleoptera, Coccinellidae) individuals in the short‐term (3 h) and long‐term (24 h). Feeding and oviposition responses were not affected when M. sexmaculatus females were exposed to larvae or adults of Scymnus pyrocheilus Mulsant (Coleoptera, Coccinellidae) beetles or larvae of the syrphid fly Ischiodon scutellaris (Fabricius) (Diptera: Syrphidae). The ratio of eggs laid to numbers of aphids consumed by M. sexmaculatus females was also affected by the presence of conspecific or C. transversalis larvae. The results suggest that fecundity of this predator may be affected by both conspecific and heterospecific competitors in a patchy resource.

Larval interactions in aphidophagous predators: effectiveness of wax cover as defence shield of Scymnus larvae against predation from syrphids

Small‐sized predators in the aphidophagous guild of Aphis gossypii Glover colonies on hibiscus trees in Japan exploit aphids at low prey abundance. Scymnus (Pullus) posticalis Sicard beetles were the first predatory species to attack aphids in the spring, and their larvae co‐occurred with larvae of Eupeodes freguens (Matsumura) syrphids in aphid‐infested leaves of hibiscus for 3 weeks in absence of large‐sized coccinellid predators. Larval interaction between Scymnus and syrphid predators was examined in relation to effectiveness of wax cover of Scymnus against predation from syrphids. Waxless first instar larvae were not protected but wax‐covered larvae of second, third and fourth instars were protected from predation by syrphid larvae. The protection was lower in the second instar which has a thin wax cover and significantly higher in the third and fourth instars having a thick wax cover. In addition, larvae from which the wax was removed were significantly more vulnerable to predation. Vulnerability of Scymnus larvae to predation from syrphids was directly related to the thickness of wax cover. Results suggest that the wax cover of Scymnus larvae act as an effective defence mechanism against predation from syrphid larvae.

Prey Consumption and Oviposition of the Aphidophagous Predator Menochilus sexmaculatus (Coleoptera: Coccinellidae) in Relation to Prey Density and Adult Size

Abstract Effects of prey density and adult predator size on food consumption and oviposition were evaluated in an aphidophagous ladybird beetle, Menochilus sexmaculatus (F.), from tropical Asia. Both the functional response and reproductive numerical response showed an upper asymptote at 40 adult Aphis craccivora Koch/female/150 cm2. Proportions of aphids consumed and eggs laid by female beetles were highest at lower aphid densities, i.e., five or 10 adult aphids. Ratio of eggs laid to aphids consumed, by dry weight, was highest at the lowest aphid density, i.e., five adult aphids. Larval food supply significantly influenced the size of adult females. After 24 h, smaller females consumed significantly fewer aphids and laid fewer eggs in comparison to larger females, but conversion efficiency from food to eggs remained the same irrespective of the difference in adult size. Results suggested that this ladybird species exploit prey efficiently at low density.

Biology, Ecology and Control Efficiency of the Aphid Parasitoid Trioxys indicas: a Review and Bibliography

ABSTRACT The present paper reviews available studies on the biology, ecology and con Trioxys indicus, a polyphagous endoparasitoid of aphids infesting agricultural crops and vegetables, viz., Aphis craccivora and A. gossypii, and presents an up-to-date bibliography. The courtship and mating behaviour, host selection, fecundity, oviposition pattern, development, longevity, sex ratio and density responsiveness behaviour as well as various physico-chemical and biological factors influencing the biology of the parasitoid are described and compared with other aphidiids. Likewise the seasonal history, hyperparasitism, host association and distribution of T. indicus are also presented. Out of 24 aphid hosts of T. indicus recorded, 21 belong to the Aphidinae. Eleven species of hyperparasitoids are recorded. The laboratory culture technique, storage of the mummies at low temperature, release methods and field release of T. indicus are included in the control efficiency section. The mummy stage of the parasitoid is...

Fast–slow continuum in the life history parameters of ladybirds revisited

A previous study of the rate of development of larvae of aphidophagous and coccidophagous ladybirds indicated that they both had the same lower developmental threshold (Ldt) but that the coccidophagous species developed more slowly than the aphidophagous species. The current analysis of the rates of development of the eggs of 48 species belonging to 8 tribes, which were kept at a range of different temperatures, indicates that ladybirds do not all have the same Ldt, but that the of eggs of aphidophagous Coccinellini develop faster than those of coccidophagous Chilocorini and more importantly those of the aphidophagous genus Scymnus and the coccidophagous Nephus, both belonging to the same robust tribe, the Scymnini, also differ, with those of the latter genus developing more slowly. Possible reasons for this are discussed.

Variation in butterfly diversity and unique species richness along different habitats in Trishna Wildlife Sanctuary, Tripura, northeast India

Quantification of butterfly diversity and species richness is of prime importance for evaluating the status of protected areas. Permanent line transect counts were used to record species richness and abundance of butterfly communities of different habitat types in Trishna wildlife sanctuary. A total of 1005 individuals representing 59 species in 48 genera belonging to five families were recorded in the present study. Of these, 23 species belonged to the family Nymphalidae and accounted for 38.98% of the total species and 45.20% of the total number of individuals. Mature secondary mixed moist deciduous forest showed the maximum diversity and species richness, while exotic grassland showed minimum diversity and species richness. Out of 59 species, 31 are new records for Tripura state, while 21 are unique species and nine are listed in the threatened category. This study revealed that mature secondary forests are more important for butterfly communities, while exotic grasslands have a negative impact on species composition.

A Comparison of Fitness Characters of Two Host Plant-Based Congeneric Species of the Banana Aphid, Pentalonia Nigronervosa and P. Caladii

Abstract Aphids and other phytophagous insects often show intra-specific variations in relation to host plant utilization. In several instances, intra-species variations lead to host-plant specialization. These are considered to be important source of speciation. In a recent study (Foottit RG et al. 2010. Zootaxa 2358: 25–38) two forms of the banana aphid, Pentalonia nigronervosa f typica Coquerel (Hemiptera: Aphididae) from banana hosts and P. nigronervosa f. caladii van der Goot collected from Zingiberaceae and Araceae respectively were described as separate species, P. nigronervosa Coquerel and P. caladii van der Goot, based on morphological and molecular differences. A study was undertaken to examine the ecological and biological characters in asexual wingless morphs of the two forms of P. nigronervosa sensu lat. using taro (Araceae) and banana (Musaceae) as host plants. The results showed consistent differences between the two forms. In biological characters, the apterous morphs off. caladii from taro host plants were found to be significantly more fecund, showed a higher net reproductive rate, longer reproductive duration, and their adults lived longer than the f. typica aphids from banana host plants. In ecological characters, f. caladii aphids formed bigger colonies and in significantly less time on taro plants in comparison to f. typica aphids which formed smaller colonies in significantly more time on banana plants. Reciprocal transfer of the two forms of P. nigronervosa aphids between their host plant species lowered performance on the transferred host plants. These results confirmed that P. nigronervosa f. typica from banana hosts and P. nigronervosa f. caladii from taro hosts are indeed two different species in relation to host plant utilization and suggested that the observed differences in their fitness characters represented distinct genotypes.