José R. Gonçalves

Insecticide selectivity to the parasitic mite Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) on Rhyzopertha dominica (Fabr.) (Coleoptera: Bostrichidae)

The presence of natural enemies in stored grains and the need of pest control alternatives led to the assessment of the effect of insecticides on the mite species Acarophenax lacunatus (Cross & Krantz), an egg parasite of the stored grain pest Rhyzopertha dominica (Fabr.). The insecticides bifenthrin, deltamethrin, pirimiphos-methyl and fenitrothion were tested at 0.4, 0.5, 0.8 and 10 ppm, respectively. Insecticide treated wheat grains were spread in petri dishes and infested with 25 adults of R. dominica. Seven days later, three mites were added to each dish, in four replicates. The number of adults of R. dominica, grain weight loss and instantaneous rate of increase (ri) of A. lacunatus were lower when the grain was treated with deltamethrin. Bifenthrin, fenitrothion, and pirimiphos-methyl were less effective in controlling the pest, but they were selective in favor of the mite, showed higher number of physogastric females and ri of A. lacunatus. Therefore, deltamethrin was less selective in favor of the mite species. Nonetheless the parasitic mite was able to parasitize eggs of R. dominica on wheat treated with all the insecticides evaluated.

Pyrethroid-Acarophenax lacunatus interaction in suppressing the beetle Rhyzopertha dominica on stored wheat.

Any biocontrol agent used against stored grain insects will have to interact with insecticides used as grain protectants due to their heavy use especially in tropical areas. Therefore, the interaction between the pyrethroid insecticides bifenthrin and deltamethrin and Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae), an egg parasite of the stored cereal pest Rhyzopertha dominica(F.) (Coleoptera: Bostrichidae), was assessed in a range of mite densities and insecticide doses for each compound. Despite the mite species presence on all insecticide doses, the lowest instantaneous rate of increase of A.lacunatus was recorded with the highest doses of insecticides. The presence of the biological control agent at all doses of both insecticides suggests its tolerance to these compounds. A. lacunatusshowed higher parasitism rate with bifenthrin than with deltamethrin indicating a higher selectivity of the first compound to the biocontrol agent.

Suscetibilidade de Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) ao enxofre

The laboratory rearing of Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) is frequently infested by the parasite mite Acarophenax lacunatus (Cross and Krantz) (Prostigmata: Acarophenacidae). This study was aimed at evaluating the sulfur doses, an effective acaricide against A. lacunatus, not harmful to the development of with R. dominica. The experimental units were Petri dishes containing 30g of whole wheat grains powdered with the different doses of the sulfur (0.0, 0.6, 0.9, 1.2, 1.5, 3.0, 6.0, 12.0, 24.0 and 48.0mg a i g-1) infested with 30 adults of R. dominica, in ten replicates. All treatments were maintained under controlled conditions (30±1°C, 60±5% r h and 24h scotophase) for 60 days after the insect infestation. Sulfur doses higher than 3.0mg a i g-1 negatively affected R. dominica development.

Biologia de Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) sobre Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) e Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae)

The aim of the present study was to assess the effect of six different temperatures on the development of Acarophenax lacunatus (Cross & Krantz) using eggs of Tribolium castaneum (Herbst) and Cryptolestes ferrugineus (Stephens) as hosts. The temperature affected the development of A. lacunatus. The largest values for the progeny (19 mites in T. castaneum and 15 mites in C. ferrugineus) were obtained at about 30 degrees C, as also observed for the net reproductive rate (Ro), which revealed that the A. lacunatus population increased 18 times in T. castaneum and 14 times in C. ferrugineus in a generation. The intrinsic rate of increase (r m) gradually increased with temperature, reaching the maximum value at 35 degrees C in T. castaneum (1,608) and C. ferrugineus (1,289). The generation time was negatively correlated with temperature, ranging from 1,60 to 4,85 days in T. castaneum and from 1,96 to 5,34 days in C. ferrugineus. These results suggest that the mite A. lacunatus may be used in programs of biological control of T. castaneum and C. ferrugineus in the tropics.

Parasitismo de Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) sobre Dinoderus minutus (Fabr.) (Coleoptera: Bostrichidae)

Published information on biological control of stored product insects by mites is meagre, although these arthropods are frequently found in the grain mass. The experiment was carried out aiming to assess the parasitism of the biological control agent Acarophenax lacunatus (Cross & Krantz) on populations of Dinoderus minutus (Fabr.). The experimental units consisted of 1.7 L glass jars containing 100 g of dry cassava, infested with 20 adults of D. minutus. Three days afterwards, four female physogastric mites were inoculated on each experimental unit. Four replicates were used for each treatment. It was observed that the mite has higher biotic potential than the host D. minutus. The egg parasitism (%) showed a high efficiency of A. lacunatus as a biological control agent of D. minutus, what led to a significant decrease of beetle populations. There was also a decrease in cassava weight loss due to the mite presence. Up to this data, A. lacunatus was reported parasitizing only eggs of R. dominica, however this report broadens the possibility of using this mite species in integrated pest management programs in storage environments.

Associação de deltametrina com Acarophenax lacunatus e seu impacto sobre o desenvolvimento de Rhyzopertha dominica

The objective of this work was to evaluate the development of Rhyzopertha dominica on wheat grain treated with the insecticide deltamethrin and infested with the mite Acarophenax lacunatus. The experimental units were Petri dishes containing 30 g of wheat grain (13% moisture content) sprayed with different doses of deltamethrin (0.00, 0.125, 0.25, 0.375, 0.50, 0.625, 0.75, 0.875 and 1.00 mg a.i. kg -1 ) infested with 30 adults of R. dominica. Five days after the infestation, five mites were inoculated on each experimental unit, in seven replicates. All treatments were maintained under controlled conditions (30±1°C, 60±5% r.h. and 24 hours scotophase) for 60 days after the infestation. The instantaneous rate of increase of R. dominica was negative under doses higher than 0.25 mg a.i. kg -1 . The lowest number of immature R. dominica was observed with the interaction between deltamethrin doses smaller than 0.5 mg a.i. kg -1 and A. lacunatus.

Dispersão de Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) em trigo armazenado, sob condições artificiais

Ability to disperse is fundamental for a successful natural enemy in a stored grain environment. The objective of the present work was to assess whether the mite Acarophenax lacunatus (Cross & Krantz) disperses in a grain mass to locate its host Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae). The experiment was based on the release of physogastric females of A. lacunatus on the surface of glass containers containing Petri dishes with 20 adults of R. dominica at different depths (4, 8, 12, 16 and 20 cm). The Petri dishes were covered with voil to prevent insect escape. Dispersion of the progeny of these physogastric females was assessed 10, 20 and 30 days after the beginning of the experiment. The mites were able to disperse and they were observed at every depth and at every period of assessment. Nonetheless, the number of A. lacunatus decreased with the increasing depth, with highest values observed at the lowest depths after 20 and 30 days of storage. It is possible that evaluations conducted in periods longer than 30 days of the parasite release could demonstrate an increase in parasitism at higher depths. The results indicated that A. lacunatus actively disperse for up to 20 cm on its own, without the assistance of its host for phoresy.

Suscetibilidade de Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) ao enxofre

The parasitic mite Acarophenax lacunatus (Cross & Krantz) is a potentially important biocontrol agent of stored grain insect pests, but its presence in insect mass rearing is undesirable. This study was carried out to evaluate the susceptibility of A. lacunatus to sulfur. The experimental units were petri dishes containing 30 g of whole wheat grains infested with 30 adults of Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae). The treatments consisted of pulverizing the wheat grains with sulfur, at 0, 0.15, 0.3, 0.6, 0.9 and 1.2 mg a.i./g, in five replicates. Three inoculations of A. lacunatus were carried out in each petri dish at five, ten and fifteen days after infestation with R. dominica. The petri dishes were stored for 60 days at 30 +/- 1 degree Celsius, 60 +/- 5% R.H. and 24h scotophase. The parasitic mite was susceptible to all sulfur doses used in the test. The number of eggs of R. dominica parasitized by A. lacunatus showed a decreasing trend with the increase in doses of sulfur, as did the number of physogastric females of the mite. The mite showed a negative correlation of their instantaneous rate of increase with sulfur dose. No mites developed at sulfur doses higher than 0.3 mg a.i./g. The susceptibility of A. lacunatus to sulfur is an important aspect to consider in the control of this parasitic mite in colonies of R. dominica. In addition, this control method has low cost and is easy to use.

Interação da temperatura com o ácaro parasita Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) sobre o desenvolvimento de Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae)

The objective of this study was to evaluate the effect of different temperatures with the association of the mite Acarophenax lacunatus (Cross & Krantz) on the population suppression of Rhyzopertha dominica (Fabricius). The experimental units were petri dishes containing 40 g of whole wheat grains (13% moisture content) infested with 10 adults of R. dominica, under the temperatures of 20, 25, 30 and 35 masculineC, with or without A. lacunatus, in five replicates. Relative humidity of 60 +/- 5% and escotophase of 24h were used for all temperatures. Five days after the infestation, five mites were inoculated in each experimental unit. The evaluations were carried out at 20, 40, 60, 80, 100 and 120 days after R. dominica infestation. The interaction of the temperature with the parasite A. lacunatus was an important tool for the population suppression of R. dominica. In temperatures higher than 25 masculineC, however, despite the reduction of the immature stages of R. dominica, there was a high grain weight loss after 120 days. The maintenance of the temperature of the wheat grains stored at 20 masculineC can be used to complement the biological control of R. dominica with A. lacunatus.

Interação entre Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) e Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae) sobre Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae)

The interaction between Acarophenax lacunatus (Cross & Krantz) and Anisopteromalus calandrae (Howard) may be a promising tool for the integrated pest management of stored grain insect pests. The objective of this study was to evaluate the compatibility of these two natural enemies on Rhyzopertha dominica (Fabricius). The experimental units were petri dishes (140 x 10 mm) containing 30 g of whole wheat grains (13% water content) infested with 20 adults of R. dominica. The treatments consisted of inoculation of A. lacunatus and A. calandrae, separately and associated, in eight replicates. Three inoculations of five adult females of the natural enemies were carried out in each petri dish at five, ten and fifteen days after the infestation of R. dominica. All treatments were stored during 60 days in environmental chamber at 30 +/- 1 degrees C, 60 +/- 5% relative humidity and 24 h scotophase. The smallest numbers of physogastric females of A. lacunatus and of adults of A. calandrae were obtained when the natural enemies were in association. The use of A. calandrae alone demonstrated a low instantaneous rate of increase (r(i)) of R. dominica and a high protection of the wheat grains. The association of A. calandrae with A. lacunatus led to the lowest number of immatures of R. dominica. These results demonstrate the importance of this interaction as a tool of for the integrated management of R. dominica in stored wheat grains.