Does temperature modify slow and fast development in two aphidophagous ladybirds?

Development within a population is known to vary with abiotic and biotic factors. However, instances of slow and fast development, i.e. different development rates within the same egg batch or cohort, have not yet been rigorously investigated in many organisms. The present study was undertaken to assess the influence of an exogenous cue, temperature (15, 20, 25, 30 and 35 °C), on slow and fast development and its effect on reproductive attributes in two ladybird species, Menochilus sexmaculatus (Fabricius) and Propylea dissecta (Mulsant) (Coleoptera: Coccinellidae). A clear bimodal pattern of distribution with two peaks was found at each temperature where the first peak represented the fast developers and the second peak slow developers. Variation in ratio and development of slow and fast developers within a cohort at different temperatures was observed to ascertain whether the phenomenon has a purely genetic basis or is environmentally influenced. The ratio of slow and fast developers in a cohort differed with temperature but not with species. Slow developers showed a female biased sex ratio and low body mass. Fast developing females laid higher numbers of eggs with higher egg viability than slow developing ones. More slow developers were found at low temperature (15 and 20 °C), equal numbers at medium temperature (25 °C) and less at higher temperature (30 and 35 °C). Results of the study are indicative of stability of the slow and fast development in the egg batch and the likelihood that the variation observed at emergence was owing to exogenous cues influenced differential rates of mortality.     

Effect of photoperiod on slow and fast developing individuals in aphidophagous ladybirds,Menochilus sexmaculatus and Propylea dissecta (Coleoptera: Coccinellidae)

The effects of environmental parameters on insect development have been studied extensively. But the reasons for 2 differential developmental rates within same cohort under varying environmental factors have not been explored. For the purpose, in this study the existence and stability of slow and fast development under 5 photoperiods (i.e., 8L: 16D, 10L : 14D, 12L : 12D, 14L : 10D and 16L : 8D; light and dark hours per day) and its effect on body mass and reproductive attributes in 2 aphidophagous ladybirds, Menochilus sexmaculatus (Fabricius) and Propylea dissecta (Mulsant) was examined on Aphis craccivora Koch at 27 ± 1 °C temperature. A clear bimodal (2 peaks, where the first peak represented the fast developing and the 2nd peak slow developing individuals) pattern of distribution at each photoperiod was found. The proportion of slow and fast developing individuals in a cohort differed with photoperiods. The slow developing individuals were more in numbers at 8L : 16D, in equal numbers at 14L : 10D and in less numbers at 16L: 8D, indicating that the variation in emergence was owing to exogenous cues influenced differential rates of mortality. Slow developing individuals had female biased sex ratio, higher longevity and lower body mass than fast developing individuals. Fast developing females laid higher numbers of eggs with higher egg viability than slow developing females. Study of such variations in development at different photoperiods is helpful to understand its role in the development of insects particularly ladybirds and permits the selection of fast developing bioagents for their use in biocontrol of pest species.     

Evaluation of Darwin's fecundity advantage hypothesis in Parthenium beetle,Zygogramma bicolorata

In the Parthenium beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), variation in body size exists between and within the sexes. The females are larger than the males. Darwin (1874) proposed the fecundity advantage hypothesis, that is, large‐sized females produce more progeny, with subsequent studies supporting, as well as, refuting the hypothesis. Thus, in order to evaluate whether this hypothesis stands in Z. bicolorata we performed experiments to investigate the role of body size in influencing: (i) assortative mating; (ii) reproductive attributes; and (iii) growth, development and survival of offspring. It is the first attempt in this beetle. We found that size influenced assortative mating, reproductive output and offspring fitness. Larger males and females were preferred as mates over smaller ones. The pairs, having larger adults as mates, had higher fecundity, while the egg viability was influenced by the male size only. The offspring of larger parents had fast development and higher survival, indicating thereby possible better nutrient allotment by the female and supply of accessory gland proteins by the male in addition to better quality of genes.     

Stage specific feeding attributes and mobilization of nutrients in Mexican beetle,Zygogramma bicolorata Pallister on Parthenium hysterophorus L.

Parthenium hysterophorus L. (Asteraceae) is a toxic weed of agricultural farms, pastures and wastelands with a pan-tropical distribution. The weed causes a reduction in crop production of agricultural fields and severe health problems in humans. The Mexican beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) is among the most promising candidates for the weed biocontrol. However, no previous study has evaluated assimilation of nutrients in this beetle. In the present study, feeding attributes and assimilation of nutrients by larvae of Z. bicolorata were assessed on the weed. Results revealed that the first larval instars of Z. bicolorata exhibited lowest consumption rates, and accumulated minimum concentrations of glucose, proteins and triglycerides in their body. They showed compensatory feeding, and displayed highest food utilization efficiencies and developmental rates. In contrast, the fourth larval instars exhibited higher food consumption rates and conversion efficiencies, but displayed lowest developmental rates. Accumulation of food reserves was also recorded maximum for the fourth larval instars. Overall, the findings may aid current mass-rearing efforts for Z. bicolorata in laboratories, but field trials are still needed to strengthen the present findings.     

Broadscale Specificity in a Bark Beetle–Fungal Symbiosis: a Spatio-temporal Analysis of the Mycangial Fungi of the Western Pine Beetle

Whether and how mutualisms are maintained through ecological and evolutionary time is a seldom studied aspect of bark beetle–fungal symbioses. All bark beetles are associated with fungi and some species have evolved structures for transporting their symbiotic partners. However, the fungal assemblages and specificity in these symbioses are not well known. To determine the distribution of fungi associated with the mycangia of the western pine beetle (Dendroctonus brevicomis), we collected beetles from across the insect’s geographic range including multiple genetically distinct populations. Two fungi, Entomocorticium sp. B and Ceratocystiopsis brevicomi, were isolated from the mycangia of beetles from all locations. Repeated sampling at two sites in Montana found that Entomocorticium sp. B was the most prevalent fungus throughout the beetle’s flight season, and that females carrying that fungus were on average larger than females carrying C. brevicomi. We present evidence that throughout the flight season, over broad geographic distances, and among genetically distinct populations of beetle, the western pine beetle is associated with the same two species of fungi. In addition, we provide evidence that one fungal species is associated with larger adult beetles and therefore might provide greater benefit during beetle development. The importance and maintenance of this bark beetle–fungus interaction is discussed.     

Redescription and Life History of Contortylenchus brevicomi,a Parasite of the Southern Pine Beetle Dendroctonus frontalis

Larval and adult life stages are described for Contortylenchus brevicomi (Massey) Rühm parasitizing a Mississippi population of Dendroctonus frontalis, the southern pine beetle. Fourth-stage larvae and free-living adult females of this species are identified and described for the first time. The life cycle of C. brevicomi can be reconstructed from this study. The adult female nematode lays eggs in a mature beetle. Larval development progresses within the hemocoel until fourth-stage larvae exit the host. Mating occurs in beetle galleries and only females enter an immature beetle host.     

Sex Ratio and Body Mass of Adult Herbivorous Beetles Depend on Time of Occurrence and Light Conditions

Body mass and sex ratio (F/M) of folivorous insects are easily measured parameters that are commonly used to assess the effect of food quality, living conditions, and preferences on the selection of favourable sites for offspring. A study was conducted on the polyphagous beetle, Gonioctena quinquepunctata (a pest of the native Prunus padus and alien P. serotina) and on the monophagous beetle, Altica brevicollis coryletorum (a pest of Corylus avellana). Both species have a similar life cycle with emergence of current-year adults in summer, and reproduction of 1-year-old insects in spring. A. brevicollis coryletorum feeds primarily on sunlit shrubs, while G. quinquepunctata prefers shaded leaves. The present study assessed the effect of time of occurrence (insect age) on body mass in both sexes and on the sex ratio F/M, taking into account the influence of light conditions associated with their favoured food source (sunlit vs. shaded leaves). We hypothesized that a change in body mass in current-year insects would be determined by the amount of consumed food, while the sex ratio would be stable, when in 1-year-old insects females would die shortly after oviposition, while males would be active for a prolonged time. Results confirmed the hypothesis that changes in mass of current-year beetles was determined by the amount of food intake. We also found that in spring, unfertilized females coexist with fertilized ones and that the latter females live for some time after oviposition; resulting in fluctuations of the mean mass for females. In both species, 1-year-old beetles were heavier than current-year. The preference of A. brevicollis coryletorum for sunlit leaves results in a higher body weight than in G. quinquepunctata in both seasons. The data are consistent and indicate seasonal fluctuations in body mass and changes in the sex ratio in 1-year-old beetles, due to the entrance into their reproductive period.     

Effect of the Nematode Contortylenchus brevicomi on Gallery Construction and Fecundity of the Southern Pine Beetle

Field-collected Dendroctonus frontalis were reared in a controlled environment. Male-female beetle pairs retrieved from galleries 1, 2, or 5 wk after introduction into pine bolts were examined for nematode parasites. Data were obtained for each pair on gallery length, egg niche construction, egg viability, and progeny survival. In a separate study, beetle pairs were reared under laboratory conditions for 10 wk. The number of emerged adult progeny of each pair was recorded. Contortylenchus brevicomi, a nematode parasite, was found in 25% of all beetles that established galleries. After 2 and 3 wk, female beetles infected with the nematode had produced fewer eggs and shorter galleries than did uninfected females. Uninfected females mated with nematode-infected males showed similar trends, although the differences in the 2- and 3-wk tests were not significant. Progeny survival or egg viability was not affected by nematode parasitism of either parent beetle. Unikaryon minutum, a microsporidian parasite found in 65% of all colonizing beetles, had no effect on measured variables. The lower fecundity of beetles parasitized by C. brevicomi continued throughout the insect''s reproductive cycle. After 10 wk, nematode-infected beetle pairs produced fewer emerged adult progeny than did uninfected pairs.     

Regulation of vitellogenin synthesis by juvenile hormone analogue in Coccinella septempunctata

Vitellogenesis in the lady beetle, Coccinella septempunctata, is controlled by juvenile hormone (JH). When immature females were reared on an artificial diet, they were characterized by hypertrophy of the fat bodies and slow development of the ovaries. Vitellogenin (Vg) synthesis in the fat body remained at a very low level throughout adult development. RNA synthesis also stayed at a relatively low level. Treatment with hydroprene induced vitellogenesis in these non-fecund females. Stimulation in Vg synthesis in hormone-treated females was demonstrated both in vivo and in fat body culture. Synthesis of fat body RNA also increased after hormone treatment. Fat body RNA from hormone-treated females directed the synthesis of Vg polypeptides both in Xenopus oocytes and in a reticulocyte lysate. Thus the induction of Vg synthesis by JH involves an increase in the level of translatable Vg mRNA.     

Temperature and altitude modulate feeding attributes of Mexican beetle,Zygogramma bicolorata Pallister on Parthenium hysterophorus

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) is an effective biocontrol agent of Parthenium hysterophorus L. which is an alien invasive herbaceous weed with a pan-tropical distribution. The present study aimed to assess the effects of temperature and altitude on feeding attributes (consumption rate, conversion efficiency and growth rate) of adults from the wild populations of Z. bicolorata inhabiting India and Nepal. Results revealed that adults inhabiting areas of low temperature (24°C ‒ 25°C) and high altitude (415 m ‒1400 m) were large and had higher food consumption rates. In contrast, those inhabiting areas of high temperature (34°C ‒ 36°C) and low altitude (81 m ‒ 229 m) were smaller and had higher food utilization efficiencies. In all the eco-climatic regions, females were larger than males and had higher feeding attributes than their counterparts. Temperature between 27°C and 30°C was found optimal for Z. bicolorata adults to convert and utilize the food biomass to body mass. Above the optimal temperature the feeding attributes decreased. Present results suggest that there exists a possibility for decrease in body size, and thereby weed biocontrol efficiency of Z. bicolorata adults with an increase in temperature due to global climate change.     

Reproductive competition promotes the evolution of female weaponry

Secondary sexual traits in females are a relatively rare phenomenon. Empirical studies have focused on the role of male mate choice in their evolution; however, recently it has been suggested that secondary sexual traits in females are more likely to be under selection via reproductive competition. We investigated female competition and the influence of female phenotype on fitness in Onthophagus sagittarius, a species of dung beetle that exhibits female-specific horns. We compared reproductive fitness when females were breeding in competition versus breeding alone and found that competition for breeding resources reduced fitness for all females, but that smaller individuals suffered a greater fitness reduction than larger individuals. When females were matched for body size, those with the longest horns gained higher reproductive fitness. The fitness function was positive and linear, favouring increased horn expression. Thus, we present evidence that female body size and horn size in O. sagittarius are under directional selection via competition for reproductive resources. Our study is a rare example of female contest competition selecting for female weaponry.     

Genetic and phenotypic relationships between immune defense,melanism and life-history traits at different temperatures and sexes in Tenebrio molitor

Insect cuticle melanism is linked to a number of life-history traits, and a positive relationship is hypothesized between melanism and the strength of immune defense. In this study, the phenotypic and genetic relationships between cuticular melanization, innate immune defense, individual development time and body size were studied in the mealworm beetle (Tenebrio molitor) using three different temperatures with a half-sib breeding design. Both innate immune defense and cuticle darkness were higher in females than males, and a positive correlation between the traits was found at the lowest temperature. The effect of temperature on all the measured traits was strong, with encapsulation ability and development time decreasing and cuticle darkness increasing with a rise in temperature, and body size showing a curved response. The analysis showed a highly integrated system sensitive to environmental change involving physiological, morphological and life-history traits.     

The Invasive American Weed Parthenium hysterophorus Can Negatively Impact Malaria Control in Africa

The direct negative effects of invasive plant species on agriculture and biodiversity are well known, but their indirect effects on human health, and particularly their interactions with disease-transmitting vectors, remains poorly explored. This study sought to investigate the impact of the invasive Neotropical weed Parthenium hysterophorus and its toxins on the survival and energy reserves of the malaria vector Anopheles gambiae. In this study, we compared the fitness of An. gambiae fed on three differentially attractive mosquito host plants and their major toxins; the highly aggressive invasive Neotropical weed Parthenium hysterophorus (Asteraceae) in East Africa and two other adapted weeds, Ricinus communis (Euphorbiaceae) and Bidens pilosa (Asteraceae). Our results showed that female An. gambiae fitness varied with host plants as females survived better and accumulated substantial energy reserves when fed on P. hysterophorus and R. communis compared to B. pilosa. Females tolerated parthenin and 1-phenylhepta-1, 3, 5-triyne, the toxins produced by P. hysterophorus and B. pilosa, respectively, but not ricinine produced by R. communis. Given that invasive plants like P. hysterophorus can suppress or even replace less competitive species that might be less suitable host-plants for arthropod disease vectors, the spread of invasive plants could lead to higher disease transmission. Parthenium hysterophorus represents a possible indirect effect of invasive plants on human health, which underpins the need to include an additional health dimension in risk-analysis modelling for invasive plants.     

Benefits of polyandry in Parthenium beetle,Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae)

The influence of polyandry on the reproductive performance of females and on offspring fitness in Zygogramma bicolorata Pallister was investigated using four experimental treatments, viz. (A) monandrous, limited mating, (B) monandrous, unlimited mating, (C) polyandrous, no-choice limited mating, and (D) polyandrous, mate choice unlimited mating. Polyandrous females had higher reproductive performance than monandrous ones. Monandrous females subjected to unlimited matings had higher egg viability than those subjected to limited matings, but fecundity did not differ significantly. In polyandrous females, the freedom to choose mates did not affect reproductive performance. However, offspring of polyandrous females allowed mate choice developed fastest and had the highest survival at 25, 27, and 30 °C. Thus, polyandry in Z. bicolorata appears to provide both direct (material) and indirect (genetic) benefits resulting in better reproductive performance and increased adaptability of the offspring to counter environmental stresses. The present study not only adds to the knowledge of reproductive biology of Z. bicolorata but it could also be of economic value as it may help in the mass rearing of Z. bicolorata and in the management of Parthenium hysterophorus.     

The pattern and range of movement of a checkered beetle predator relative to its bark beetle prey

Theoretical studies of predator‐prey population dynamics have increasingly centered on the role of space and the movement of organisms. Yet, empirical studies have been slow to follow suit. Herein, we quantified the long‐range movement of a checkered beetle, Thanasimus dubius, which is an important predator of a pernicious forest pest, the southern pine beetle, Dendroctonus frontalis. Adult checkered beetles were marked and released at five sites and subsequently recaptured at traps baited with pine and pine beetle semiochemicals and located at distances up to 2 km away from the release point. While the pattern of recaptures‐with‐distance at each site provided a modest fit to a simple random‐diffusion model, there was a consistent discrepancy between observed and expected recaptures: a higher than expected proportion of beetles were recaptured at the more distant traps. To account for this deviation, we developed a model of diffusion that allowed for simple heterogeneity in the population of marked beetles; i.e., a slow and fast moving form of the checkered beetle. This model provided a significantly better fit to the data and formed the basis for our estimates of intra‐forest movement. We estimated that on average, one half of the checkered beetles dispersed at least 1.25 km, one third dispersed>2 km, and 5% dispersed>5 km. The source of the heterogeneous dispersal rates were partially due to differences in beetle size: smaller beetles (for both males and females) were more likely to be recaptured away from the release site than larger beetles. The southern pine beetle (prey for the checkered beetle) exhibited no significant heterogeneity in dispersal ability and provided a very good fit to the simple diffusion model. The only difference in dispersal between these two species was that checkered beetles were undergoing greater long‐distance dispersal than the pine beetles (the radius containing 95% of the dispersing individuals was 5.1 km for the checkered beetle and 2.3 km for the pine beetle). Data on the movement of these two species is used to evaluate a general model of spatial pattern formation in a homogeneous environment, and the potential of the checkered beetle as a biological control agent for the southern pine beetle.     

Evolution of slow and fast development in predatory ladybirds

The frequency distribution of the durations of development of 516 larvae of Adalia bipunctata is unimodal, and the fast‐ and slow‐developing larvae can be identified at the beginning of the fourth (=last) instar. To determine the advantages of fast and slow development, the survival, duration of development, growth and number of aphids consumed by fast‐ and slow‐developing fourth instar larvae fed different numbers aphids were recorded. The percentages of fast‐ and slow‐developing fourth instar larvae that survived when fed 0.5, 1 or an excess of aphids per day, surprisingly, did not differ. The slow‐developing larvae of both sexes took longer to complete their development than the fast‐developing larvae when fed 1 or an excess of aphids per day, and although the weights of the fast‐ and slow‐developing fourth instar larvae differed at the beginning of the instar, they did not differ at the end of this instar when fed 1 aphid per day. However, when reared on an excess of aphids per day, the adult weights of the fast‐developing individuals was greater than that of slow‐developing individuals. The average durations for which the larvae in the two groups survived when fed 0.5 aphids/day differed with the larvae of the fast‐developing individuals surviving for 9.8 ± 0.5 days and slow‐developing individuals 17 ± 1.3 days. Assuming that it is the rate of predator biomass increase, which is maximized by evolution, a model of the relationship between the rate of development/growth of a predator and that of its prey indicates that the optimum growth rate of a predator is positively associated with that of its prey. The evolutionary implications of these results are discussed.     

Reproductive Consequences of Male Arrival Order in the Bark Beetle, Ips grandicollis

For group-living animals the choice of whether to join aggregations or initiate their own is influenced by potential benefits such as group protection and reduced energetic expenditure, as well as costs such as competition for food and mates. The bark beetle Ips grandicollis is an invasive pest species that colonises recently felled timber in Australian pine (Pinus spp.) plantations. Male beetles initiate colonies by burrowing under the bark of trees and emitting an aggregation pheromone which attracts conspecifics, including a harem of females with whom they mate. We predicted that males that initiated colonies, or who arrived early, would have larger harems than later arrivals (due to decreased competition for females). However, we found the opposite effect with early-arriving males actually associated with fewer females than later arriving males, although this may have resulted from some females leaving harems as they get older. We conclude that pioneering does not improve male likelihood of attracting females in Ips grandicollis, at least initially, but it may provide advantages for offspring when competing for food during development.     

Experimental Evolution of a Trypanosome Parasite of Bumblebees and its Implications for Infection Success and Host Immune Response

Selection on basic growth properties of parasites may have many consequences for parasite traits, infection outcome, or host responses to infection. It is known that genotypes (strains) of the trypanosome parasite of bumblebees Crithidia bombi vary widely in their growth rates in their natural host, Bombus terrestris, as well as when cultured in medium. To test for changes in growth rates and their consequences, we here experimentally evolved six strains of C. bombi for fast and slow growth under controlled conditions in culture medium. Subsequently, we infected the evolved lines in live host and found that lines selected for slow growth attained higher infection intensity in the live bumblebee than those evolved for fast growth, whilst the immune response of the host was the same to both kinds of lines. These results fit the expectation that attenuation through rapid adaptation to a different environment, the culture medium, makes the parasite less successful in its next host. Selection for fast growth therefore does not necessarily lead to higher parasite success or more transmission. Hence, insect trypanosome pathogens can be attenuated by experimental evolution in the culture; this could inform important aspects of host-parasite evolution and perhaps vaccine development.     

Costs and benefits of reproduction in predaceous ladybird: Effect of multiple matings on reproduction and offspring development

A few matings are sufficient for females to maximize their reproductive success, while male fitness usually increases with an increase in the number of matings. However, females of a majority of insects mate multiple times. This presents an evolutionary puzzle and brings an understanding that some benefits are associated with it. Therefore, to understand the costs and benefits of multiple matings, we performed an experimental study in a ladybird beetle, Anegleis cardoni and observed reproductive performance and longevity of adults as direct benefits and offspring development and survival as indirect benefits. This is the first time that the effect of multiple matings is being evaluated on offspring development and survival in a ladybird beetle. Results clearly reveal that females directly benefit from multiple matings in terms of increased lifetime fecundity and egg viability, but their longevity decreases with increased number of matings. Best-fit curves on lifetime fecundity and percent egg viability revealed that maximum fecundity and egg viability were both attained after 17 matings. Developmental duration of offspring decreased and their survival increased with an increase in number of matings. Developmental duration was shortest after 20 matings and longest after a single mating.     

Influence of age at mating on the reproductive performance of Parthenium beetle,Zygogramma bicolorata (Coleoptera: Chrysomelidae)

Abstract Age-specific mating incidence, sexual maturation and effect of age at mating on reproductive performance of the Parthenium beetle, Zygogramma bicolorata Pallister, was studied. Based on 50% mating incidence the calculated age of sexual maturation of males and females was 10.5 and 11.1 days, respectively, which was not statistically significant. However, on the basis of age at first mating, that is, sexual maturity, females matured 2 days earlier than males. Fecundity, pre-oviposition, oviposition and post-oviposition period and female longevity appear to be influenced by female age at mating with reproductive performance peaking at 30 days. On the other hand, egg viability was influenced by male age and was highest when males mated at the age of 40 days. To summarise, egg production and timing of egg deposition was female age-dependent, whereas egg fertility was male age-dependent. It was also observed that females mated at a later age and laid a higher number of eggs immediately after mating than did earlier mated females. This was ostensibly in a bid to increase fitness by maximizing reproductive output in the reduced life span available. This is the first investigation on the effect of age of females at mating on reproduction in this beetle.