Optimal Pest Control Strategies with Cost-effectiveness Analysis.

Pest and plant diseases cause damages and economic losses, threatening food security and ecosystem services. Thus, proper pest management is indispensable to mitigate the risk of losses. The risk of environmental hazards induced by toxic chemicals alongside the rapid development of chemical resistance by insects entails more resilient, sustainable, and ecologically sound approaches to chemical methods of control. This study evaluates the application of three dynamical measures of controls, namely, green insecticide, mating disruption, and the removal of infected plants, in controlling pest insects. A model was built to describe the interaction between plants and insects as well as the circulation of the pathogen. Optimal control measures are sought in such a way they maximize the healthy plant density jointly with the pests' density under the lowest possible control efforts. Our simulation study shows that all strategies succeed in controlling the insects. However, a cost-effectiveness analysis suggests that a strategy with two measures of green insecticide and plant removal is the most cost-effective, followed by one which applies all control measures. The best strategy projects the decrease of potential loss from 65.36% to 6.12%.

Reproductive Dominance Strategies in Insect Social Parasites.

In eusocial insects, the high cost of altruistic cooperation between colony members has favoured the evolution of cheaters that exploit social services of other species. In the most extreme forms of insect social parasitism, which has evolved multiple times across most social lineages, obligately parasitic species invade the nests of social species and manipulate the workforce of their hosts to rear their own reproductive offspring. As alien species that have lost their own sociality, these social parasites still face social challenges to infiltrate and control their hosts, thus providing independent replicates for understanding the mechanisms essential to social dominance. This review compares socially parasitic insect lineages to find general trends and build a hypothetical framework for the means by which social parasites achieve reproductive dominance. It highlights how host social organization and social parasite life history traits may impact the way they achieve reproductive supremacy, including the potential role of chemical cues. The review discusses the coevolutionary dynamics between host and parasite during this process. Altogether, this review emphasizes the value of social parasites for understanding social evolution and the need for future research in this area.

Change in children's school behavior after mass administration of praziquantel for Schistosoma mansoni infection in endemic areas of western Kenya: A pilot study using the Behavioral Assessment System for Children (BASC-2).

BACKGROUND: Schistosomiasis is a parasite-related chronic inflammatory condition that can cause anemia, decreased growth, liver abnormalities, and deficits in cognitive functioning among children. METHODOLOGY/PRINCIPAL FINDINGS: This study used the Behavior Assessment System for Children (BASC-2) to collect data on thirty-six 9-12 year old school-attending children's behavioral profiles in an Schistosoma mansoni-endemic area of western Kenya, before and after treatment with praziquantel for S. mansoni infection. BASC-2 T scores were significantly reduced post-treatment (p < 0.05) for each of the 'negative' behavior categories including externalizing problems (hyperactivity, aggression, and conduct problems that are disruptive in nature), internalizing problems (anxiety, depression, somatization, atypicality, and withdrawal), school problems (academic difficulties, included attention problems and learning problems), and the composite behavioral symptoms index (BSI), signifying improved behavior. While the observed improvement in the 'positive' behavior category of adaptive skills (adaptability, functional communication, social skills, leadership, and study skills) was not statistically significant, there were significant improvements in two adaptive skills subcategories: social skills and study skills. CONCLUSION/SIGNIFICANCE: Results of this study suggest that children have better school-related behaviors without heavy S. mansoni infection, and that infected children's behaviors, especially disruptive problem behaviors, improve significantly after praziquantel treatment.

Effect of crop plants on fitness costs associated with resistance to Bacillus thuringiensis toxins Cry1Ac and Cry2Ab in cabbage loopers.

Fitness costs associated with resistance to Bacillus thuringiensis (Bt) toxins critically impact the development of resistance in insect populations. In this study, the fitness costs in Trichoplusia ni strains associated with two genetically independent resistance mechanisms to Bt toxins Cry1Ac and Cry2Ab, individually and in combination, on four crop plants (cabbage, cotton, tobacco and tomato) were analyzed, in comparison with their near-isogenic susceptible strain. The net reproductive rate (R0) and intrinsic rate of increase (r) of the T. ni strains, regardless of their resistance traits, were strongly affected by the host plants. The ABCC2 gene-linked mechanism of Cry1Ac resistance was associated with relatively low fitness costs, while the Cry2Ab resistance mechanism was associated with higher fitness costs. The fitness costs in the presence of both resistance mechanisms in T. ni appeared to be non-additive. The relative fitness of Bt-resistant T. ni depended on the specific resistance mechanisms as well as host plants. In addition to difference in survivorship and fecundity, an asynchrony of adult emergence was observed among T. ni with different resistance mechanisms and on different host plants. Therefore, mechanisms of resistance and host plants available in the field are both important factors affecting development of Bt resistance in insects.

Blood parasites mediate morph-specific maintenance costs in a colour polymorphic wild bird.

Parasites can mediate profound negative effects on host fitness. Colour polymorphism has been suggested to covary genetically with intrinsic physiological properties. Tawny owl colour polymorphism is highly heritable with two main morphs, grey and brown. We show that experimental medication acts to reduce blood parasites and that medicated grey females maintain body mass during breeding, whereas medicated brown females decline in body mass similar to control females of both morphs. We find no effect of medication on general immunoglobulin levels, antigen-specific humoral response or H/L ratio. In the descriptive data, both morphs have similar blood parasite infection rates, but blood parasite infection is associated with decreased body mass in brown but not in grey females. We conclude that blood parasite infection primarily has somatic costs, which differ between the two highly heritable tawny owl colour morphs with more pronounced costs in the grey (little pigmented) morph than in the brown (heavily pigmented) morph. Because our descriptive results imply the opposite pattern, our findings highlight the need of experimental manipulation when studying heritable variation in hosts' response to parasitism.

Exploring the contributions of bed nets, cattle, insecticides and excitorepellency to malaria control: a deterministic model of mosquito host-seeking behaviour and mortality.

Domestic and personal protection measures against malaria exposure either divert host-seeking vectors to other hosts or kill those attempting to feed. Here, we explicitly model mosquito host-seeking processes in the context of local host availability and elucidate the impacts and mechanisms of pyrethroid-treated bed nets in Africa. It has been suggested that excitorepellent insecticides could increase exposure of unprotected humans by concentrating mosquito biting activity on this vulnerable group. This worst-case scenario is confirmed as a possibility where vector populations lack alternative hosts, but an approximate 'break-even' scenario, with users experiencing little overall change in exposure, is more likely because of increased mosquito mortality while foraging for resources. Insecticidal nets are predicted to have epidemiologically significant impacts on transmission experienced by users and non-users at levels of coverage that can be achieved by sustainable net distribution systems, regardless of excitorepellency or the ecological setting. The results are consistent with the outcome of several randomised controlled trials, predicting enormous reductions in transmission at individual and community levels. As financial support, technology and distribution systems for insecticide-treated nets improve, massive reductions in malaria transmission could be realised.

Assessment of host resistance to Trichinella spiralis in mice following preinfection exposure to 2,3,7,8-TCDD.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been reported to decrease host resistance to a variety of infectious agents when exposure occurs prior to infection. Resistance to viral infection has been observed at doses as low as 0.1 microgram TCDD/kg body wt, well below the thymolytic dose in mice. In the present study, female B6C3F1 mice were exposed to a single intraperitoneal injection of 0, 0.1, 1.0, 10.0, or 30.0 micrograms TCDD/kg 7 days prior to infection to determine the effects of TCDD exposure on resistance to the nematode parasite Trichinella spiralis. Exposure to 10 or 30 micrograms TCDD/kg delayed adult parasite elimination from the small intestine. Significantly more larvae were released by female parasites and greater numbers of encysted larvae were recovered from the muscle of mice exposed to TCDD. Proliferative responses of splenocytes and mesenteric lymph node cells stimulated with T. spiralis antigen were significantly suppressed at exposure levels of TCDD > or = 1.0 microgram/kg 7 days after infection and in splenocytes only at 14 days after infection, demonstrating the greater sensitivity of proliferative responses to TCDD exposure than actual host resistance to Ts infection. Suppressed proliferation was observed at doses which produced TCDD concentrations > or = 0.2 pmol/g of lymphoid tissue on Day 7 of infection. In addition, it was determined that infected mice had higher TCDD levels than noninfected mice given the same dose. These results suggest an interaction between TCDD exposure and infection, i.e., that exposure to TCDD altered the host response to infection, while infection delayed elimination of TCDD from the host.