Silica Nanoparticles for Insect Pest Control.

To date, control strategies used against insect pest species are based on synthetic insecticide applications. In addition, the efficacy of these treatments could be decreased due to insecticide resistance in insect populations. Also, the irrational use of chemical control strategies has negative consequences of non-target organisms and threatening human health. Designing nanomaterial for pest insect control is a promising alternative to traditional insecticide formulations. In particular, it has been proven that silica nanoparticles have the potential for molecules delivery, release control improvement and also their toxicity as insecticide alone. In this work, we summarized the state of knowledge on silica nanoparticles (SiNPs) used in pest insect management. Besides, aspects of their synthesis, mode of action, and toxic effects on non-target organisms and environment are reviewed.

Esterase isoenzymes and insecticide resistance in Frankliniella occidentalis populations from the south-east region of Spain.

BACKGROUND: Frankliniella occidentalis (Pergande) is among the most important crop pests in the south-east region of Spain; its increasing resistance to insecticides constitutes a serious problem, and understanding the mechanisms involved is therefore of great interest. To this end, F. occidentalis populations, collected from the field at different locations in south-east Spain, were studied in terms of total esterase activity and esterase isoenzyme pattern. RESULTS: Individual thrips extracts were analysed by native polyacrylamide gel electrophoresis (PAGE) and stained for esterase activity with the model substrate alpha-naphthyl acetate. Significant correlations were found between resistance to the insecticides acrinathrin and methiocarb and the presence of a group of three intensely stained bands, named Triplet A. For each individual thrips extract, total esterase activity towards the substrates alpha-naphthyl acetate and alpha-naphthyl butyrate was also measured in a microplate reader. Insects possessing Triplet A showed a significantly higher alpha-naphthyl acetate specific activity and alpha-naphthyl acetate/alpha-naphthyl butyrate activity ratio. This observation allowed a reliable classification of susceptible or resistant insects either by PAGE analysis or by total esterase activity determination. CONCLUSION: The PAGE and microplate assays described can be used as a monitoring technique for detecting acrinathrin- and methiocarb-resistant individuals among F. occidentalis field populations.

Gold-nanoparticles ingestion disrupts reproduction and development in the German cockroach.

The present work shows the effects of gold nanoparticles (AuNPs) orally administered on reproduction and development of the insect Blattella germanica. Newly emerged females were provided with food containing AuNPs (87.44µg/g) of a size between 15 and 30nm (mean 21.8nm), and were allowed to mate with males. Food ingestion, mortality, reproductive parameters (time to ootheca formation and eclosion, ootheca viability and fertility) as well as postembryonic developmental parameters of the first ootheca (nymphal survival and life span) were recorded throughout the experiment. Gold from AuNPs was accumulated by adults of B. germanica with a bioaccumulation factor of 0.1. Ingestion of AuNPs did not disturb the time for ootheca formation nor ootheca eclosion. However, ootheca viability was decreased almost by 25% in AuNPs treated females in comparison to controls. At the same time the number of hatched nymphs was decreased by 32.8% (p<0.001) in AuNP group respect to control one. The postembryonic developmental parameters were also affected by AuNPs treatment, with a 35.8% of decrease (p<0.01) in number of nymphs that moulted to second and third instars and a reduction of their life span. Ingestion of AuNPs causes sublethal effects in B. germanica that compromises life-traits involved in population dynamics. B. germanica is proposed as a model species in nanotoxicological studies for urban environments.

Evaluation of metabolic detoxifying enzyme activities and insecticide resistance in Frankliniella occidentalis.

The western flower thrips Frankliniella occidentalis (Pergande) is a very significant pest of a number of different agricultural crops in the south-east of Spain. The importance of thrips as a pest is not due mainly to the direct damage inflicted on the plant, but to the loss in commercial value which occurs as a consequence of the development of dark spots caused by the tomato spotted wilt virus (TSWV) which they transmit. The economic threshold is therefore almost zero, which enhances the problems of resistance management. The present work is part of a global project that attempts to evaluate the status of insecticide resistance in field populations of thrips obtained from several agricultural crops. We have studied, in either individual or pooled insects, some enzyme systems classically related to detoxification of insecticides: esterase and glutathione-S-transferase (GST). The activity of these enzymes from laboratory populations selected with various classes of insecticides has also been measured using several appropriate substrates. An increase in GST mean activity was found in two field-collected strains. Differences in frequency distributions of esterase and GST activities were found for both field-collected strains and for a laboratory strain selected with acrinathrin. These activities were compared with those of a wild-type reference strain.