Does the non-native Harlequin ladybird disrupt the feeding behaviour of the native two-spot ladybird?

Since its arrival in 2004, the non-native Harlequin ladybird Harmonia axyridis (Coleoptera: Coccinellidae) has rapidly spread throughout Britain, and it is now the most common coccinellid in England. There have since been concerns about the detrimental effects it may have on native coccinellids because there is a strong correlation between the arrival of H. axyridis and the decline in native species, including the two-spot ladybird, Adalia bipunctata. However, there have been few studies of the behavioural interactions between these two species, which occupy a high-niche overlap. This study investigated if the presence of H. axyridis impacts the feeding behaviour of A. bipunctata through direct competition for aphid prey. Foraging and interactive behaviour of A. bipunctata and H. axyridis were investigated within microcosms. Adalia bipuncata exhibited a similar consumption rate and time in the presence of H. axridis, yet H. axyridis consumed 3.5 times more prey items and were seven times faster compared to A. bipuncata. Observations showed that H. axyridis does not directly disrupt the feeding behaviour of A. bipunctata, but rather indirectly excludes the native species through being a superior competitor for prey items. Results indicate that the decline in native coccinellid species may be a consequence of H. axyridis competitive advantage, but that the concept of coexistence should not be dismissed.

Prey quantity affects development, survival and reproductive attributes of Coccinella transversalis Fabricius, 1781 under laboratory conditions

This study assessed development, survival and reproductive parameters of a ladybird beetle, Coccinella transversalis Fabricius, 1781 on different quantities (viz. scarce, optimum and abundant) of the bean aphid prey, Aphis craccivora under laboratory conditions (27 ±1°C; 65 ±5% relative humidity and 14 light: 10 dark hours photoperiod). The pre-oviposition period was the shortest (6.40 ±0.40 days) on abundant prey and longest (9.20±0.49 days) on scarce prey. The oviposition period significantly increased with increasing prey quantity, being longest (55.10 ±1.75 days) on abundant prey and shortest (38.50 ±2.14 days) on scarce prey. Lifetime fecundity and egg viability were recorded the highest (1604.10 ±45.61 eggs and 90.82 ±0.80%, respectively) on abundant diet and lowest (794.60 ±30.84 eggs and 82.72 ±0.67%, respectively) on scarce diet. Reproductive rate, reproductive time ratio, longevity of male and female were all highest, i.e. 29.20 ±0.61 egg/day, 3.70 ±0.26, 65.80 ±1days and 70.30 ±1.30 days, respectively on abundant diet. These parameters were lowest, i.e. 20.90 ±0.83 eggs/day, 1.95 ±0.16, 58.80 ±1.60 days and 56.20 ±1.75 respectively on scarce diet. Development was fastest on abundant prey followed by optimum and slowest on scarce prey. Percentage pupation, percent adult emergence, developmental rate, growth index and generation survival were all highest, i.e. 84.00 ±3.68%, 79.00 ±4.09%, 0.077 ±0.00 day-1, 3.50 ±0.19 day-1, 0.54 ±0.05, respectively when larvae were reared on abundant prey. The same parameters were lowest, i.e. 65.00 ±04.79%, 57.00 ±4.99%, 0.062 ±0.001 day-1, 10.46 ±0.11 day-1, 0.25 ±0.0, respectively on scarce prey. It may therefore be concluded that the availability of abundant prey enhances developmental and reproductive parameters of C. transversalis, and abundant diet of aphid prey may be used for better mass culture of ladybird beetles in laboratories for augmentative biological control of aphids.

Feeding location of aphid prey affects life history traits of a native predator

The green peach aphid (GPA), Myzus persicae S., and the cabbage aphid (CA), Brevicoryne brassicae L., exhibit a feeding preference when exposed to different canola (Brassica napus L.) plant structures. Preference may be associated with the concentration and/or composition of allelochemicals; specifically, glucosinolates (GLS). Furthermore, each aphid species employs a different strategy for tolerating plant defensive chemistry; GPA excretes glucosinolates while CA sequesters these toxic compounds. Given these different detoxification mechanisms, it is possible that both feeding location and aphid species may affect prey suitability for Hippodamia convergens larvae. We conducted a factorial laboratory experiment to evaluate whether one or both factors impacted predator fitness. We hypothesized that plant structures with higher GLS concentrations will negatively affect the development and survival of immature predators, which will also vary based on prey detoxification strategies. Results confirm that when predators fed on either aphid species reared on canola structures having lower GLS concentrations, development was faster than when they fed on aphids reared on structures having higher GLS. Although predators consumed more GPA than CA, consumption rates did not differ between rearing location for GPA, but fewer CA were consumed when reared on reproductive canola parts. These findings suggest that: 1) plant-mediated differences in prey quality exist for canola aphids; 2) the type of adaptation used by aphids to overcome plant defenses have important consequences for prey suitability; and 3) reduced feeding by H. convergens larvae on unsuitable prey may offset deleterious effects of plant defenses against aphid pests. By evaluating source-sink dynamics at the plant level, we can further understand trophic interactions involving plant defenses and how these interactions may influence community dynamics and structure.

No nutritional benefits of egg cannibalism for Coleomegilla maculata (Coleoptera: Coccinellidae) on a high-quality diet

Egg cannibalism serves various functions in the Coccinellidae. Here we examined the fitness consequences of egg cannibalism by neonates, fourth instar larvae, and prereproductive adults of Coleomegilla maculata DeGeer, with beetles fed a diet of Ephestia kuehniella Zeller eggs. Cannibalism of two eggs by neonates had no effect on development, and cannibalism of five eggs by fourth instars did not benefit any aspect of reproduction, but delayed pupation slightly. Cannibalism of eggs by pre-reproductive adults had no effect on reproductive success in any combination of reciprocal crosses of cannibals and non-cannibals. Females did not recognize, nor avoid consuming, their own clutches, and cannibalism propensity did not change following mating and onset of oviposition in either sex. These results contrast with those for more strictly aphidophagous species in which larvae gain developmental benefits, and females may recognize and avoid filial egg clusters while using cannibalism to interfere with conspecific females, whereas males reduce egg cannibalism after mating because they cannot recognize filial clusters. Egg cannibalism may confer developmental benefits to C. maculata when diet is suboptimal, as previously shown, but no such benefits were evident on the high-quality E. kuehniella egg diet. Female C. maculata do not require aphids to reproduce and distribute their eggs broadly in the environment, given that larvae can develop on pollen and non-aphid prey. Thus, C. maculata is not subject to the intraspecific competition that selects for cannibalism in more aphidophagous species, and also lacks many secondary adaptations associated with the behaviour.