nan Omkar

Ecology and biological control application of multicoloured Asian ladybird, Harmonia axyridis: A review

Abstract The ecology of and biological control by multicoloured Asian ladybird beetle, Harmonia axyridis (Pallas) are reviewed. Our emphasis is on assembling and interpreting information on general characteristics, invasion and establishment, sexual activity, foraging and predation, development, survival and reproduction, predator–predator interactions, natural enemies, biocontrol, non-target effects and status of H. axyridis as a pest of fruits. Colonization of H. axyridis for aphid biocontrol in the USA have been successful in terms of its establishment, but its abundance is turning out to be a nuisance to humans. Its harmful non-target impact on beneficial organisms, humans and native species is becoming a debatable issue. The question on its present position, whether it is a biocontrol agent or pest, is a critical issue and discussed. Inferences from the empirical data are made and new avenues for future research are suggested.

Mating behavior of an aphidophagous ladybird beetle, Propylea dissecta (Mulsant)

Abstract The mating behavior of Propylea dissecta (Mulsant) was investigated in detail. Protandry was evident, as males mature earlier than females. Predicted age of sexual maturation of male and female ladybirds was 7.12 and 9.33 days, respectively. Males performed courtship in six steps, viz. approach, watch, examine, embrace, mount and attempt. Embrace is possibly an appeasement act, while examine serves to recognize mate. Chemical signals initiate male attraction toward females. Visual and tactile cues appear to secondarily help in mate recognition. Mating lasted longest (275.40±12.23 min) when it occurred between unmated individuals. It was much shorter (176.60±5.60 min) when prior mated individuals copulated. There was a significant decrease in mating durations when adults were subjected to five successive matings. Fecundity and percent egg viability increased significantly with increase in the number of matings.

Temperature-dependent life attributes of an aphidophagous ladybird, Propylea dissecta

Reproductive attributes, age-specific fecundity and natality based life-tables of an aphidophagous ladybird, Propylea dissecta (Mulsant) were investigated at five temperatures, using aphid, Aphis gossypii as prey. Pre-oviposition period decreased significantly with increase in temperature up to 27°C and thereafter increased at a slower rate. Egg viability dropped significantly at temperature extremes. Females lived longer than males; however, longevity decreased significantly with increase in temperature. The predicted total fecundity and oviposition rate were 952.54 eggs and 35.15 eggs per day at 27°C predicted by a mathematical model compared to empirical estimates of 856.00±30.00 eggs and 39.7±2.26 eggs per day. Age-specific fecundity was triangular and temperature dependent. The peak in oviposition rate occurred earlier at higher temperatures. The highest values of net reproductive rate (Ro=431.1), intrinsic rate of increase (rm=0.2134 day−1) and finite rate of increase (λ=1.2379 day−1) were recorded at 27°C, which suggests it is the optimum temperature for the mass rearing of P. dissecta.

Expression of an insecticidal fern protein in cotton protects against whitefly

Whitefly (Bemisia tabaci) damages field crops by sucking sap and transmitting viral diseases. None of the insecticidal proteins used in genetically modified (GM) crop plants to date are effective against whitefly. We report the identification of a protein (Tma12) from an edible fern, Tectaria macrodonta (Fee) C. Chr., that is insecticidal to whitefly (median lethal concentration = 1.49 μg/ml in in vitro feeding assays) and interferes with its life cycle at sublethal doses. Transgenic cotton lines that express Tma12 at ∼0.01% of total soluble leaf protein were resistant to whitefly infestation in contained field trials, with no detectable yield penalty. The transgenic cotton lines were also protected from whitefly-borne cotton leaf curl viral disease. Rats fed Tma12 showed no detectable histological or biochemical changes, and this, together with the predicted absence of allergenic domains in Tma12, indicates that Tma12 might be well suited for deployment in GM crops to control whitefly and the viruses it carries.

Optimal number of matings in two aphidophagous ladybirds

Abstract.  1. The present study was designed to identify the optimal number of matings required for maximum fecundity and egg viability in two aphidophagous ladybirds, Cheilomenes sexmaculata and Propylea dissecta.

Effect of age on reproductive attributes of an aphidophagous ladybird, Cheilomenes sexmaculata

The effect of both male and female age was investigated on certain reproductive attributes, viz. mating incidence, mating duration, fecundity, percent egg viability, ratio of reproductive and non‐reproductive periods and reproductive rate, of an aphidophagous ladybird, Cheilomenes sexmaculata (Fabricius). Females started mating at the age of 8 hours post‐emergence (PE) and males at the age of 2 days PE. Mating in the laboratory was a male‐dominated phenomenon. The mating duration and reproductive rate of 10‐day‐old females when mated with males of varying ages increased up to the male age of 60 days, and thereafter decreased, whereas, fecundity, egg viability and ratio of reproductive and non‐reproductive periods increased up to the male age of 50 days, and thereafter declined. However, when females of varying ages were mated with 10‐day‐old males, fecundity and reproductive rate increased up to 40 days of female age, respectively, then decreased. The ratio of reproductive and non‐reproductive periods increased with increasing age of females. Mating age for optimal reproductive output was 10J50‐day‐old males and NE to 40‐day‐old females. Reproductive cessation in males was recorded after 50 days PE, whereas in females at the age of 40 days PE. Higher mating durations lead to elevated reproductive rates. Delay in the reproductive phase was positively correlated with longevity. The results of this study may aid mass multiplication of this ladybird by identifying and promoting usage of adults of optimal age. Our results also enhance our understanding of the effect of age on reproductive attributes in ladybirds.

Intrinsic advantages of Cheilomenes sexmaculata over two coexisting Coccinella species (Coleoptera: Coccinellidae)

Abstract Development, survival and reproductive performance of coexisting ladybird species, viz. Cheilomenes sexmaculata, Coccinella septempunctata, and Coccinella transversalis, of the tribe Coccinellini were studied and compared to assess their coexistence and ecological relationships. High values of life history parameters, viz. developmental rate, immature survival, fecundity, egg viability, reproductive rate and conversion of efficiency of ingested food were recorded for C. sexmaculata followed by C. transversalis and C. septempunctata suggesting that the former has intrinsic advantages over the latter two species. This could possibly counterbalance its disadvantages, like relatively smaller size and weight, thereby making it competitive. The developmental period increased with increase in body size. Exceptionally high fecundity after single mating has been recorded in C. sexmaculata. The egg viability, however, was lower than in both Coccinella species.

REPRODUCTIVE BEHAVIOUR OF TWO APHIDOPHAGOUS LADYBEETLES, CHEILOMENES SEXMACULATA AND COCCINELLA TRANSVERSALIS

Abstract  Reproductive behaviour of two aphidophagous ladybeetles, Cheilomenes sexmaculata and Coccinella transversalis was studied. A premating period of 5.0±0.5 and 11.7±0.4 days and a pre‐oviposition period of 5.5±0.7 and 12.7±0.5 days was observed for C. sexmaculata and C. transversalis, respectively. Males of both the species exhibited courtship in five steps, viz. approach, watch, examine, mount and attempt. Sexually immature, recently mated and ovipositing females rejected male advances in both the species. Chemical, visual and behavioural cues probably play a role in mate recognition. Quiescent mating occurred in C. sexmaculata, whereas abdominal shakings in the form of bouts and strokes were characteristic in C. transversalis. C. sexmaculata had a relatively prolonged mating duration (133.4±z8.9 min) than C. transversalis (37.9±2.0 min), possibly due to the absence of active processes, i.e., bouts and strokes. The active processes in C. transversalis decreased with multiple matings in a day. Unmated adults of both the species mated more vigorously than the mated ones. Reproductive performance of both the species was best after multiple matings.

Development and immature survival of two aphidophagous ladybirds, Coelophora biplagiata and Micraspis discolor

Abstract The developmental parameters, namely developmental periods, larval survival, adult emergence, growth index, developmental rate and sex ratio in terms of female proportion in a population of two aphidophagous ladybirds, namely, Coelophora biplagiata (Swartz) and Micraspis discolor (Fabricius) were investigated, using three aphid species as prey. The immature stages of C. biplagiata were significantly affected by prey quality and developed fastest when fed on Aphis craccivora followed by Aphis gossypii and Rhopalosiphum maidis. The order of prey suitability in terms of developmental rate of immature stages of M. discolor was just reversed. The adult females were heavier than males, while pre‐pupae were heavier than pupae in both ladybirds. The sex ratio of adult emergence, though female‐biased in both ladybird species, was not significantly affected by prey quality.

Why do neonates of aphidophagous ladybird beetles preferentially consume conspecific eggs in presence of aphids

Abstract The neonates of aphidophagous ladybird beetles, Propylea dissecta, Coccinella transversalis and Coelophora saucia preferentially consumed conspecific eggs in presence of essential aphid prey, Aphis gossypii. This preference was strongest in P. dissecta and recorded in all density combinations of conspecific eggs and aphids. The neonates of all three species developed faster resulting in heavier second instars with lower mortality when fed on conspecific eggs as compared to mobile or defenceless aphids. In addition, they required less dry biomass of conspecific eggs than that of aphids. These results reveal that neonates are benefitted intrinsically when they feed on conspecific eggs. The neonates of P. dissecta exhibited discrimination for more nutritious food, as they contacted and ate conspecific eggs more frequently than aphids as their first meal. This discrimination was not found in Coccinella transversalis and Coelophora saucia possibly due to their bigger sizes and possible higher energy requirements. Although, the major effect of chemical cues was only noticed in P. dissecta, it could be concluded that chemicals (surface and within) of conspecific eggs possibly attract neonates for egg–cannibalism, as both eggs and aphids were consumed in greater numbers when coated with egg extracts. The reverse occurred when eggs and aphids were coated with aphid extracts.