Dietary stress increases the susceptibility of Tribolium castaneum to Beauveria bassiana

The Potential of Two Entomopathogenic Fungi and Enhanced Diatomaceous Earth Mixed with Abamectin: A Comprehensive Study on Mortality, Progeny Production, Application Method, and Surface Application against Tribolium castaneum

This study determined the efficacy of Beauveria bassiana (Bals. -Criv.) Vuill., Metarhizium anisopliae (Metchnikoff) Sorokin, and diatomaceous earth mixed with abamectin (DEA) alone and in their combinations for the integrated management of larvae and adults of Tribolium castaneum (Herbst) from three field populations of Pakistan (Multan, Rawalpindi, and Rahim Yar Khan) and one laboratory population (Faisalabad). Treatments were applied on three surfaces, namely, viz. steel, concrete, and jute bags, implementing two application methods, dusting and spraying. The combined treatments were more effective in comparison with single treatments for both larvae and adults. Overall, the highest mortality rates were recorded in the Faisalabad population, followed by the Rehaim Yar Khan, Rawalpindi, and Multan populations. Progeny production was suspended 21 days after exposure to the combined treatment of DEA and both fungi in all populations except Rawalpindi. Larvae were found to be more susceptible than adults in all treatments and intervals. Dusting was more efficient than spraying for both larvae and adults and for all the populations studied. The present study provides a wholistic understanding of the impact of different factors on the success of the combined treatments using DEA and entomopathogenic fungi, supporting their use as surface treatments.

Resource limitation has a limited impact on the outcome of virus-fungus co-infection in an insect host

Infection by pathogens is strongly affected by the diet or condition of the prospective host. Studies that examine the impact of diet have mainly focused on single pathogens; however, co-infections within a single host are thought to be common. Different pathogen groups might respond differently to resource availability and diverse infections could increase the costs of host defense, meaning the outcome of mixed infections under varying dietary regimes is likely to be hard to predict. We used the generalist cabbage looper, Trichoplusia ni and two of its pathogens, the DNA virus T. ni nucleopolyhedrovirus (TniSNPV) and the entomopathogenic fungus, Beauveria bassiana to examine how nutrient reduction affected the outcome of mixed pathogen infection. We challenged insects with a low or high effective dose of virus, alone or combined with a single dose of fungus. We manipulated food availability after pathogen challenge by diluting artificial diet with cellulose, a non-nutritious bulking agent, and examined its impact on host and pathogen fitness. Reducing diet quantity did not alter overall or pathogen-specific mortality. In all cases, TniSNPV-induced mortality was negatively affected by fungus challenge. Similarly, B. bassiana-induced mortality was negatively affected by TniSNPV challenge, but only at the higher virus dose. Dietary dilution mainly affected B. bassiana speed of kill when mixed with a high dose of TniSNPV, with an increase in the duration of fungal infection when cellulose was low (high quantity). One pathogen dominated the production of transmission stages in the cadavers and co-infection did not affect the yield of either pathogen. There was no evidence that co-infections were more costly to the survivors of pathogen challenge. In conclusion, dietary dilution did not determine the outcome of mixed pathogen infection, but it had more subtle effects, that differed between the two pathogens and could potentially alter pathogen recycling and host-pathogen dynamics.

Do dietary stresses affect the immune system of Periplaneta americana (Blattaria: Blattidae)?

Stresses can be caused by multiple biotic and abiotic factors and their effects can affect both the biology and the immune system of insects. American cockroach - Periplaneta americana (Linnaeus, 1758) (Blattaria: Blattidae) -besides being an excellent model species, has great medical importance because it can act as a mechanical vector of several pathogens. This study aimed to evaluate the influence of starvation, dehydration and both stresses on weight, and total and differential haemocyte count in P. americana adults. Each specimen was isolated in glass flasks containing or not food and/or water. They were weighed periodically. Another group received water for 24 h after the end of stress period. In the immunologic bioassay, we counted their haemocytes after the final weighing. All stresses reduced the insect weight, especially when the stresses were combined. Females of the control group gained weight and males had it unaltered. Different stress conditions and time did not influence on total haemocyte count. Insects without food and water had the proportion of prohaemocytes increased and plasmatocytes decreased. This study can serve as a basis of further studies of bioecology, behaviour and the ability of resisting insecticides, besides serving as a model to studies in other insect species.

Infection of host plants by Cucumber mosaic virus increases the susceptibility of Myzus persicae aphids to the parasitoid Aphidius colemani

Plant viruses can profoundly alter the phenotypes of their host plants, with potentially far-reaching implications for ecology. Yet few studies have explored the indirect, host-mediated, effects of plant viruses on non-vector insects. We examined how infection of Cucurbita pepo plants by Cucumber mosaic virus (CMV) impacted the susceptibility of aphids (Myzus persicae) to attack by the parasitoid wasp Aphidius colemani. In semi-natural foraging assays, we observed higher rates of aphid parasitism on infected plants compared to healthy plants. Subsequent experiments revealed that this difference is not explained by different attack rates on plants differing in infection status, but rather by the fact that parasitoid larvae successfully complete their development more often when aphid hosts feed on infected plants. This suggests that the reduced nutritional quality of infected plants as host for aphids--documented in previous studies--compromises their ability to mount effective defenses against parasitism. Furthermore, our current findings indicate that the aphid diet during parasitoid development (rather than prior to wasp oviposition) is a key factor influencing resistance. These findings complement our previous work showing that CMV-induced changes in host plant chemistry alter patterns of aphid recruitment and dispersal in ways conducive to virus transmission.

A Ni hyperaccumulator and a congeneric non-accumulator reveal equally effective defenses against herbivory

The defense hypothesis is commonly used to explain the adaptive role of metal hyperaccumulation. We tested this hypothesis using two Brassicaceae congeneric species: Alyssum pintodasilvae, a Ni hyperaccumulator, and the non-accumulator Alyssum simplex both growing on serpentine soils in Portugal. Artificial diet disks amended with powdered leaves from each plant species were used to compare the performance (mortality, biomass change) and feeding behavior of Tribolium castaneum in no-choice and choice tests. The performance of T. castaneum was not affected at several concentrations of A. pintodasilvae or A. simplex in no-choice tests. However, the consumption of plant-amended disks was significantly lower than that of control disks, irrespectively of the species fed. Accordingly, when insects were given an alternative food choice, disks of both plant species were significantly less consumed than control disks. Moreover, insects did not discriminate between disks in the combination "A. pintodasilvae+A. simplex". Contrary to our expectations, these results suggest that both plant species have equally effective defenses against herbivory. While Ni is believed to be part of the deterrence mechanism in the hyperaccumulator A. pintodasilvae, it seems likely that organic compounds, possibly glucosinolates, play an important role in the defense of A. simplex or in both species.

The effect of food limitation on immunity factors and disease resistance in the western tent caterpillar

Epizootics of nucleopolyhedrovirus characterize declines of cyclic populations of western tent caterpillars, Malacosoma pluviale californicum. In field populations, infection can be apparently lacking in one generation and high in the next. This may suggest an increase in the susceptibility to infection of larvae at peak density or the triggering of a vertically transmitted virus. Here, we test the hypothesis that reduced food availability, as may occur during population outbreaks of tent caterpillars, influences the immunocompetence of larvae and increases their susceptibility to viral infection. We compared immunity factors, hemolymph phenoloxidase and hemocyte numbers, and the susceptibility to nucleopolyhedroviral infection of fifth instar larvae that were fully or partially fed as fourth instars. To determine if maternal or transgenerational influences occurred, we also determined the susceptibility of the offspring of the treated parents to viral infection. Food limitation significantly reduced larval survival, development rate, larval and pupal mass, moth fecundity and levels of hemolymph phenoloxidase, but not the numbers of hemocytes. Neither the food-reduced larvae nor their offspring were more susceptible to viral infection and were possibly even less susceptible at intermediate viral doses. Food reduction did not activate latent or covert viral infection of larvae as might be expected as a response to stress. We conclude that reducing the food intake of fourth instar larvae to an extent that had measurable and realistic impacts on their life history characteristics was not translated into increased susceptibility to viral infection.