Walking stability of Rhyzopertha dominica (Fabricius, 1792) (Coleoptera: Bostrichidae)

Results obtained in studies can contribute to the advancement of science and innovative methods and techniques for developing practical activities. Reporting conditions that may restrict the implementation of research is critical to ensure the optimal development of further technical studies. The objective of this study was to assess the walking stability of R. dominica on a flat and smooth surface. The study was based on the determination of mortality, morphology and walking stability of the insect outside the grain mass, on a flat and smooth surface. Mortality of adults of this Coleoptera in conditions with and without food was similar, which explains the difficulty that this insect had for accessing the food source on the flat and smooth surface. The measurements of body length (BOL), width (BOW) and height (BOH) of R. dominica were compared with those of Tribolium castaneum (Coleoptera: Tenebrionidae), which showed good ability to walk in these conditions. This study indicated that the former presents lower BOL and BOW, and greater BOH than the second, and all these variables showed differences when analyzed simultaneously by means of the construction of multivariate morphometric indices (Width × Height, Length × Height and Height × Length × Width). These morphometric variables, together with the definition of the geometry most similar to the body shape, resulted in determination of the center of gravity (CG) and static rollover threshold (SRTgeom) for both species. Rhyzopertha dominica and T. castaneum presented CGs considered high and low, respectively, and together with the values obtained for SRTgeom, may justify that R. dominica can be considered a less stable species during movement, and presents greater risk of rollover on flat and smooth surfaces.

Sublethal Exposure to Clove and Cinnamon Essential Oils Induces Hormetic-Like Responses and Disturbs Behavioral and Respiratory Responses in Sitophilus zeamais (Coleoptera: Curculionidae)

Essential oils have been suggested as suitable alternatives for controlling insect pests. However, the potential adaptive responses elicited in insects for mitigating the actions of these compounds have not received adequate attention. Furthermore, as is widely reported with traditional insecticides, sublethal exposure to essential oils might induce stimulatory responses or contribute to the development of resistance strategies that can compromise the management of insect pests. The current study evaluated the locomotory and respiratory responses as well as the number of larvae per grain produced by the maize weevil, Sitophilus zeamais Motschulsky, after being sublethally exposed to the essential oils of clove, Syzygium aromaticum L., and cinnamon, Cinnamomum zeylanicum L. The essential oils showed similar insecticidal toxicity (exposure route: contact with dried residues; Clove LC95 = 3.96 [2.78-6.75] µl/cm(2); Cinnamon LC95 = 3.47 [2.75-4.73] µl/cm(2)). A stimulatory effect on the median survival time (TL50) was observed when insects were exposed to low concentrations of each oil. Moreover, a higher number of larvae per grain was produced under sublethal exposure to clove essential oil. S. zeamais avoided the treated areas (in free-choice experiments) and altered their mobility when sublethally exposed to both essential oils. The respiratory rates of S. zeamais (i.e., CO2 production) were significantly reduced under low concentrations of the essential oils. We recommend the consideration of the potential sublethal effects elicited by botanical pesticides during the development of integrated pest management programs aiming to control S. zeamais.

Locomotory and physiological responses induced by clove and cinnamon essential oils in the maize weevil Sitophilus zeamais

Plant essential oils have been suggested as a suitable alternative for controlling stored pests worldwide. However, very little is known about the physiological or behavioral responses induced by these compounds in insect populations that are resistant to traditional insecticides. Thus, this investigation evaluated the toxicity (including the impacts on population growth) as well as the locomotory and respiratory responses induced by clove, Syzygium aromaticum L., and cinnamon, Cinnamomum zeylanicum L., essential oils in Brazilian populations of the maize weevil Sitophilus zeamais. We used populations that are resistant to phosphine and pyrethroids (PyPhR), only resistant to pyrethroids (PyR1 and PyR2) or susceptible to both insecticide types (SUS). The PyPhR population was more tolerant to cinnamon essential oil, and its population growth rate was less affected by both oil types. Insects from this population reduced their respiratory rates (i.e., CO2 production) after being exposed to both oil types and avoided (in free choice-experiments) or reduced their mobility on essential oil-treated surfaces. The PyR1 and PyR2 populations reduced their respiratory rates, avoided (without changing their locomotory behavior in no-choice experiments) essential oil-treated surfaces and their population growth rates were severely affected by both oil types. Individuals from SUS population increased their mobility on surfaces that were treated with both oil types and showed the highest levels of susceptibility to these oils. Our findings indicate that S. zeamais populations that are resistant to traditional insecticides might have distinct but possibly overlapping mechanisms to mitigate the actions of essential oils and traditional insecticides.

Ozone toxicity and walking response of populations of Sitophilus zeamais (Coleoptera: Curculionidae)

Ozone is a recognized alternative to the fumigants methyl bromide and phosphine for the control of stored product insects. However, as with fumigants in general, the potential sublethal effects of ozone on targeted insect species may compromise its efficacy and has yet to be investigated. Here, we determined ozone toxicity of 30 field-collected populations of the maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae), and assessed the walking response of adult insects from these populations to sublethal ozone exposure. Time-mortality toxicity to ozone at 50 ppm concentration in a continuous 2 liter/min flow indicated uniform susceptibility among the populations studied without any indication of ozone resistance (toxicity ratios [at LT50] > two-fold). In contrast, there was significant variation in walking activity among the maize weevil populations, which was not correlated with ozone susceptibility. This was not surprising because of the relatively uniform susceptibility to ozone among the maize weevil populations. Respiration rate affected ozone toxicity but not walking activity, whereas body mass was negatively correlated with walking activity but was not correlated with ozone toxicity. Based on our data, lower respiration rates may potentially lead to reduced ozone uptake whereas larger body mass limits walking activity. Ozone seems a promising alternative fumigant with low short-term risk of resistance development because of the high susceptibility and low variability of response to this compound. Furthermore, ozone reduces walking activity of S. zeamais that implies it likely reduces the chances of insects escaping exposure at the early stages of fumigation.

Ozone toxicity and walking response of populations of Sitophilus zeamais (Coleoptera: Curculionidae)

Ozone is a recognized alternative to the fumigants methyl bromide and phosphine for the control of stored product insects. However, as with fumigants in general, the potential sublethal effects of ozone on targeted insect species may compromise its efficacy and has yet to be investigated. Here, we determined ozone toxicity of 30 field-collected populations of the maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae), and assessed the walking response of adult insects from these populations to sublethal ozone exposure. Time-mortality toxicity to ozone at 50 ppm concentration in a continuous 2 liter/min flow indicated uniform susceptibility among the populations studied without any indication of ozone resistance (toxicity ratios [at LT50] > two-fold). In contrast, there was significant variation in walking activity among the maize weevil populations, which was not correlated with ozone susceptibility. This was not surprising because of the relatively uniform susceptibility to ozone among the maize weevil populations. Respiration rate affected ozone toxicity but not walking activity, whereas body mass was negatively correlated with walking activity but was not correlated with ozone toxicity. Based on our data, lower respiration rates may potentially lead to reduced ozone uptake whereas larger body mass limits walking activity. Ozone seems a promising alternative fumigant with low short-term risk of resistance development because of the high susceptibility and low variability of response to this compound. Furthermore, ozone reduces walking activity of S. zeamais that implies it likely reduces the chances of insects escaping exposure at the early stages of fumigation.

[Biology of Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) on Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and 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.

[Biological efficacy and persistence of biphenthrin sprayed on maize at different grain temperatures]

The objective of this work was to evaluate the immediate and latent effects of the grain temperature, during the spraying process, on the persistence and biological efficacy of the biphenthrin insecticide against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). For such, biphenthrin was sprayed on the grain at the temperatures: 25, 30, 35, 40 and 45 degrees C. To access the persistence of biphenthrin, insecticide residue analyses were carried out monthly, just after spraying until 90 days of storage. To evaluate the biological efficacy of biphenthrin, 20 adults of each species were placed in petri dishes with sprayed grain, and kept in climate cabinets under 27 degrees C and 55% of RH, during 48h. Evaluations were done every 15 days, starting just after spraying and finishing at 90 days of storage. Both persistence and biological efficacy of biphenthrin reduced as storage time and grain temperatures increased. Additionally, S. zeamais was more tolerant to biphenthrin than T. castaneum.