Sampling Scarab Beetles in Tropical Forests: The Effect of Light Source and Night Sampling Periods

Light traps have been used widely to sample insect abundance and diversity, but their performance for sampling scarab beetles in tropical forests based on light source type and sampling hours throughout the night has not been evaluated. The efficiency of mercury-vapour lamps, cool white light and ultraviolet light sources in attracting Dynastinae, Melolonthinae and Rutelinae scarab beetles, and the most adequate period of the night to carry out the sampling was tested in different forest areas of Costa Rica. Our results showed that light source wavelengths and hours of sampling influenced scarab beetle catches. No significant differences were observed in trap performance between the ultraviolet light and mercury-vapour traps, whereas these two methods caught significantly more species richness and abundance than cool white light traps. Species composition also varied between methods. Large differences appear between catches in the sampling period, with the first five hours of the night being more effective than the last five hours. Because of their high efficiency and logistic advantages, we recommend ultraviolet light traps deployed during the first hours of the night as the best sampling method for biodiversity studies of those scarab beetles in tropical forests

Increased fecundity of malathion-specific resistant beetles in absence of insecticide pressure

Despite that resistance frequency is assumed to decline when selective pressure is relaxed, the stability of resistance frequency has been observed in some insects in the absence of insecticide. In the red flour beetle, Tribolium castaneum, the first case of malathion-resistance was reported in the early 1960s. The malathion-specific resistant phenotype has now almost completely replaced the susceptible one in red flour beetle populations. In the present study, several life-history traits that could influence the fitness of the insects were compared between insecticide-susceptible and malathion-specific resistant populations of the red flour beetle. On average, egg fertility and egg-to-adult development time did not differ between susceptible and resistant populations. However, the fecundity of resistant females was greater than that of susceptible ones. Generally, differences in development time between insecticide resistant and susceptible populations are considered as having more effect on fitness than do differences in fecundity. However, the observed increased female fecundity may participate, in combination with the previously observed increased male reproductive success, to the development and the stability of malathion-specific resistance in T. castaneum

Pyrethroid insecticide evaluation on different house structures in a Chagas disease endemic area of the Paraguayan Chaco

Insecticide effects of deltamethrin 2.5% SC (flowable solution) on different substrates and triatomine infestation rates in two indigenous villages (Estancia Salzar and Nueva Promesa) of the Paraguayan Chaco are reported. This field study was carried out to determine the extent to which variability in spray penetration may affect residual action of the insecticide. A total of 117 houses in the two villages were sprayed. Filter papers discs were placed on aluminium foil pinned to walls and roofs in selected houses and the applied insecticide concentration was determined by high pressure liquid chromatography (HPLC). The target dose rate was 25 mg a.i./m(2). The mean actual applied dose in Estancia Salazar was 11.2 +/- 3.1 mg a.i./m(2) in walls and 11.9 +/- 5.6 mg a.i./m(2) in roofs while in Nueva Promesa, where duplicates were carried out, the mean values were 19.9 +/- 6.9 mg a.i./m(2) and 34.7 +/- 10.4 mg a.i./m(2) in walls and 28.8 +/- 19.2 mg a.i./m(2) and 24.9 +/- 21.8 mg a.i./m(2) in roofs. This shows the unevenness and variability of applied doses during spraying campaigns, and also the reduced coverage over roof surfaces. However wall bioassays with Triatoma infestans nymphs in a 72 It exposure test showed that deposits of deltamethrin persisted in quantities sufficient to kill triatomines until three months post spraying. Knockdown by deltamethrin on both types of surfaces resulted in 100% final mortality. A lower insecticidal effect was observed on mud walls. However three months after treatment, sprayed lime-coated mud surfaces displayed a twofold greater capacity (57.5%) to kill triatomines than mud sprayed surfaces (25%). Re-infestation was detected by manual capture only in one locality, six months after spraying

Behavioral interactions between Sitophilus zeamais and Tribolium castaneum: the first colonizer matters

There is lack of knowledge on the interactions between kernel aging and the simultaneous infestation by insects, both internal and external feeders. In the present paper, we report results obtained in arena-olfactometer assays in which we studied possible preference and behavioral relationships between the primary colonizer Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) and the secondary colonizer Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). For this purpose, three experiments were conducted. The experiment I examined the response of S. zeamais adults at the fresh or stored kernels damaged by T. castaneum adults, compared to the control and the response of T. castaneum adults at the fresh or stored kernels damaged by S. zeamais adults, compared to the control. The experiment II examined the response of S. zeamais adults at the intact fresh or stored kernels conditioned at different conditioning intervals (1, 7, and 14 days) with kernels damaged by T. castaneum, compared to the control and the response of T. castaneum adults at the intact fresh or stored kernels conditioned at different conditioning intervals (1, 7 and 14 days) with kernels damaged by S. zeamais, compared to the control. The experiment III examined the response of S. zeamais adults at kernels contaminated at different contamination intervals by larvae or adults of T. castaneum, and the response of T. castaneum adults at kernels contaminated by larvae or adults of S. zeamais. In experiment I, significantly more S. zeamais adults were found in traps containing fresh or stored kernels damaged by T. castaneum than in the controls. Significantly more T. castaneum adults were found in traps containing fresh or stored kernels damaged by S. zeamais than in the controls. In experiment II, at 7 days of conditioning, significantly more adults of S. zeamais were captured in the traps used as control than in the traps containing either fresh conditioned kernels or stored conditioned kernels. At 1 and 14 days of conditioning, significantly more adults of T. castaneum were captured in the traps that contained stored conditioned kernels damaged by S. zeamais than in the controls. In experiment III, at 1, 7, and 14 days of contamination, significantly more adults of S. zeamais were captured in traps with kernels contaminated by larvae of T. castaneum or in the traps with kernels contaminated by adult females of T. castaneum than in the controls. Significantly more S. zeamais adults were found in traps containing kernels contaminated by T. castaneum adult males than in control kernels at the 7 and 14 days of contamination. At 1 day of contamination, significantly more adults of T. castaneum were captured in traps with kernels contaminated by larvae of S. zeamais than in the controls. The results of the present study suggest that kernels which were previously infested by S. zeamais were more prone to be selected by T. castaneum adults and kernels that were previously infested by T. castaneum were more prone to be selected by S. zeamais. Thus, the first colonizer can serve as the primary colonizer of stored grains, even if this first colonizer cannot infest sound kernels. The kernel age was also a crucial issue for the attraction of S. zeamais and T. castaneum. Stored kernels exhibited a stronger influence on the attraction of T. castaneum than for S. zeamais

Initial and residual efficacy of insecticides on different surfaces against rice weevil Sitophilus oryzae (L.)

The aim of the study was to investigate how various types of storage facilities with, e.g., concrete, metal, and plywood surfaces interfere with the activity of different insecticide formulations used for rice weevil Sitophilus oryzae (L.) control: malathion (EC), pirimiphos-methyl (EC), and lambda-cyhalothrin (CS and WP). Initial and residual efficacy were determined in the laboratory. Knockdown data for the initial effects were processed by probit analysis and presented as knockdown time (KDT) parameters with kdt-p lines. Delayed effects were shown as knockdown efficacy (%) determined after 24 h of weevils’ contact with 7-, 14-, 30-, 60-, 90-, 120-, 150-, and 180-day-old deposits on each surface. Malathion (EC) and pirimiphos-methyl (EC) showed the highest initial knockdown efficacy on metal, while it was 3.6 (3.4)- and 4.4 (3.3)-fold lower on concrete and plywood, respectively. Lambda-cyhalothrin (CS and WP) showed the highest initial efficacy on concrete, and slightly lower (1.3 and 2.4) fold on metal and plywood, respectively. Both formulations of lambda-cyhalothrin and malathion on metal, as well as pirimiphos-methyl on plywood were 100 % efficient against S. oryzae 180 days after the treatment. Delayed efficacy of both formulations of lambda-cyhalothrin decreased on plywood after 120 days, and after 180 days the efficacy was 55 %. All insecticides, except lambda-cyhalothrin (CS), expressed low knockdown efficacy on concrete, while the deposit of lambda-cyhalothrin (CS) on concrete was 100 % efficient during 90 days, and after 120, 150, and 180 days the efficacy was 83, 65, and 17 %, respectively