Bioinsecticide-Predator Interactions: Azadirachtin Behavioral and Reproductive Impairment of the Coconut Mite Predator Neoseiulus baraki

Synthetic pesticide use has been the dominant form of pest control since the 1940s. However, biopesticides are emerging as sustainable pest control alternatives, with prevailing use in organic agricultural production systems. Foremost among botanical biopesticides is the limonoid azadirachtin, whose perceived environmental safety has come under debate and scrutiny in recent years. Coconut production, particularly organic coconut production, is one of the agricultural systems in which azadirachtin is used as a primary method of pest control for the management of the invasive coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae). The management of this mite species also greatly benefits from predation by Neoseiulus baraki (Athias-Henriot) (Acari: Phytoseiidae). Here, we assessed the potential behavioral impacts of azadirachtin on the coconut mite predator, N. baraki. We explored the effects of this biopesticide on overall predator activity, female searching time, and mating behavior and fecundity. Azadirachtin impairs the overall activity of the predator, reducing it to nearly half; however, female searching was not affected. In contrast, mating behavior was compromised by azadirachtin exposure particularly when male predators were exposed to the biopesticide. Consequently, predator fecundity was also compromised by azadirachtin, furthering doubts about its environmental safety and selectivity towards biological control agents.     

Comparison of two populations of the pantropical predator Amblyseius largoensis (Acari: Phytoseiidae) for biological control of Raoiella indica (Acari: Tenuipalpidae)

The red palm mite, Raoiella indica Hirst (Acari: Tenuipalpidae), was recently introduced in the Americas. It spread quickly throughout coconut palm growing areas, expanding considerably its host range. The invasion of this species has caused high economic impact in several countries. In Brazil, extensive areas are expected to be affected. For logistical reasons and other concerns, chemical control does not seem desirable for the control of this pest in most Latin American countries. Biological control of R. indica by introducing exotic natural enemies seems to be an important control measure to be considered. Surveys in many countries have shown that Amblyseius largoensis (Muma) (Acari: Phytoseiidae) is a very common predator on coconut palms. This study compared the biology of a population of A. largoensis found for a long time in association with R. indica in La Reunion Island (Indian Ocean) with a population from Roraima State (northern Brazil), where R. indica was first found about two and a half years ago. No significant differences were observed between populations in relation to the duration of different immature stages or total survivorship. However, the oviposition period, prey consumption and net reproductive rate were significantly higher for the La Reunion population, warranting further investigation to determine whether that population should be released in Roraima to control the pest.     

Trypanosoma rangeli: characterization of a Mg-dependent ecto ATP-diphosphohydrolase activity

In this work we describe the ability of living Trypanosoma rangeli to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by Trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (1.53+/-0.12 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 5.24+/-0.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. This stimulatory effect on the ATP hydrolysis was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2), SrCl(2), and ZnCl(2). The apparent K(m) for Mg-ATP2- was 0.53+/-0.11 mM. The optimum pH for the T. rangeli Mg-dependent ecto-ATPase activity lies in the alkaline range. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A1, ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, DIDS (4, 4'-diisothiocyanostylbene 2'-2'-disulfonic acid) as well as suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. This ecto-ATPase activity was stimulated by carbohydrates involved in the attachment/invasion of salivary glands of Rhodnius prolixus and by lipophorin, an insect lipoprotein circulating in the hemolymph.     

A rotatory funnel-shaped collector for trapping airborne mites in a glycerin-based adhesive surface

Many mite species disperse via the air. However, most methods described for the study of aerial dispersal have some limitations in the collection and/or recovery of mites that could be improved. The aim of this study was to describe a rotatory funnel-shaped collector that directs the wind to adhesive surfaces covered with a glycerin-based solution. Tests were conducted on a soccer field at UESC, Ilhéus, Brazil, in four 8-day periods. In total, 330 mites of 52 species of Eriophyidae, Tarsonemidae, Diptilomiopidae, Iolinidae, Triophtydeidae, Astigmata, Tydeidae, Phytoseiidae, Scutacaridae, Oribatida, Ascidae, Dolichocybidae, Eupodidae, Pygmephoridae and Tenuipalpidae were collected. Of the mites captured in the first three periods, 67% were Aceria sp. (Eriophyidae), and in the fourth period 46% were Coccotydaeolus aff. bakeri and Paurotyndareus sp. (Iolinidae). Comparisons between the funnel-shaped collector with the tube-shaped rotatable model of Duffner et al. (J Pest Sci 74:1–6, 2001, adapted from Schliesske 1977) showed that the former captured?>3× the number of mites and 2× the number of species. In conclusion, it is expected that the method described here could help in future pest management, and help solve ecological and behavioral problems involving airborne mite dispersal, offering a tool for monitoring, counting and identifying mites, or even other small arthropods, pollen and fungal spores, in experimental and applied studies.

     

Limits to ambulatory displacement of coconut mites in absence and presence of food-related cues

Ambulatory movement of plant-feeding mites sets limits to the distances they can cover to reach a new food source. In absence of food-related cues these limits are determined by survival, walking activity, walking path tortuosity and walking speed, whereas in presence of food the limits are also determined by the ability to orient and direct the path towards the food source location. For eriophyoid mites such limits are even more severe because they are among the smallest mites on earth, because they have only two pairs of legs and because they are very sensitive to desiccation. In this article we test how coconut mites (Aceria guerreronis Keifer) are constrained in their effective displacement by their ability to survive in absence of food (meristematic tissue under the coconut perianth) and by their ability to walk and orient in absence or presence of food-related cues. We found that the mean survival time decreased with increasing temperature and decreasing humidity. Under climatic conditions representative for the Tropics (27 °C and 75 % relative humidity) coconut mites survived on average for 11 h and covered 0.4 m, representing the effective linear displacement away from the origin. Within a period of 5 h, coconut mites collected from old fruits outside the perianth moved further away from the origin than mites collected under the perianth of young fruits. However, in the presence of food-related cues coconut mites traveled over 30 % larger distances than in absence of these cues. These results show that ambulatory movement of eriophyoid mites may well bring them to other coconuts within the same bunch and perhaps also to other bunches on the same coconut palm, but it is unlikely to help them move from palm to palm, given that palms usually do not touch each other.     

Characterization of lipophorin binding to the fat body of Rhodnius prolixus

In insects, lipids are transported by a hemolymphatic lipoprotein, lipophorin. The binding of lipophorin to the fat body of the hematophagous insect Rhodnius prolixus was characterized in a fat body membrane preparation, obtained from adult females. For the binding assay, purified lipophorin was radiolabelled in the protein moiety (125I-HDLp), and it was shown that iodination did not affect the affinity of the membrane preparation for lipophorin. Under incubation conditions used, lipophorin binding to membranes achieved equilibrium after 40-60 min, but this time was longer when a low concentration of lipophorin was present in the medium. The capacity of the fat body membrane preparation to bind lipophorin was abolished when membranes were pre-treated with trypsin, and it was also affected by heat. When 125I-HDLp was incubated with increasing concentrations of membrane protein, corresponding increases in binding were observed. Lipophorin binding was sensitive to pH, and it was maximal between pH 6.0 and 7.0. The specific binding of lipophorin to the fat body membrane preparation was a saturable process, with a Kd of 2.1 +/- 0.4 x 10(-7)M and a maximal binding capacity of 289 +/- 88 ng lipophorin/microgram of membrane protein. Binding to the fat body membranes did not depend on calcium, but it was affected by ionic strength, being totally inhibited at high salt concentrations. Suramin also interfered with lipophorin binding and it was abolished in the presence of 2 mM suramin, but at concentrations of 0.05 and 0.1 mM it seemed to increase binding activity slightly. Fat body membrane preparation from Rhodnius prolixus was able to bind lipophorin from Manduca sexta larvae.     

Fat body fructose-2,6-bisphosphate content and phosphorylase activity correlate with changes in hemolymph glucose concentration during fasting and re-feeding in larval Manduca sexta

Fasting of second-day fifth instar larval Manduca sexta leads to a rapid decrease in hemolymph glucose concentration from 3.39+/-0.29 to 0.33+/-0.06 mM in 1 h, along with a decrease in the fructose-2,6-bisphosphate content in the fat body (from 5.92+/-0.31 to 2.80+/-0.47 nmol fructose-2,6-bisphosphate/g fat body in 3 h) and activation of fat body glycogen phosphorylase (from 16% to 55-65% phosphorylase a). During re-feeding an increase in the glucose level in the hemolymph was observed (from 0.36+/-0.05 to 3.91+/-0.36 mM in 3 h), along with an increase in the fructose-2,6-bisphosphate level in the fat body (from 2.88+/-0.47 to 6.66+/-0.42 nmol fructose-2,6-bisphosphate/g fat body in 3 h) and inactivation of fat body glycogen phosphorylase (from 56% to 16% phosphorylase a). These data are consistent with the hypothesis that a decrease in hemolymph glucose both activates fat body glycogen phosphorylase and causes a decrease in fat body fructose-2,6-bisphosphate content. Both of these changes would favor conversion of stored glucose to trehalose in the fat body. When second-day larvae were decapitated, the changes in hemolymph glucose and fat body fructose-2,6-bisphosphate were very similar to those observed in fasting whole insects. These data are consistent with a direct role for glucose in controlling carbohydrate metabolism in Manduca sexta.     

Perimicrovillar membrane assembly: the fate of phospholipids synthesised by the midgut of Rhodnius prolixus

In this study, we describe the fate of fatty acids that areincorporated from the lumen by the posterior midgut epithelium ofRhodnius prolixus and the biosynthesis of lipids. We alsodemonstrate that neutral lipids (NL) are transferred to the haemolymphaticlipophorin (Lp) and that phospholipids remain in the tissue in which they areorganised into perimicrovillar membranes (PMMs). 3H-palmitic acid added at theluminal side of isolated midguts of R. prolixus females wasreadily absorbed and was used to synthesise phospholipids (80%) and NL (20%).The highest incorporation of 3H-palmitic acid was on the first day after a bloodmeal. The amounts of diacylglycerol (DG) and triacylglycerol synthesised by thetissue decreased in the presence of Lp in the incubation medium. The metabolicfates of 3H-lipids synthesised by the posterior midgut were followed and it wasobserved that DG was the major lipid released to Lp particles. However, themajority of phospholipids were not transferred to Lp, but remained in thetissue. The phospholipids that were synthesised and accumulated in the posteriormidgut were found to be associated with Rhodnius luminalcontents as structural components of PMMs.