Attraction of Neomegalotomus parvus (Westwood) (Heteroptera: alydidae) to cow urine and ammonia

The alydid bug parvus (Westwood) is not easily detected in the field and the discovery of attractants may be a suitable way to monitor this species. The attraction of N. parvus to traps (transparent, transparent green and yellow) baited with cow urine and ammonia was studied in two field trials. Traps were placed near a terrace with pigeon pea plants (Cajanus cajan L.). Tap water, NaCl 10% aqueous solution (w/v), cow urine, and ammonia (NH4OH 1% aqueous solution) were tested as attractants in yellow, transparent and transparent green traps. Green traps baited with cow urine caught more bugs than yellow and transparent traps (3.2 and 7.2 times more, respectively), and more bugs than traps of the same color with just water (no captures) or NH4OH solution (14.5 times more). Traps baited with ammonia caught more bugs than traps with water: 14.4, 4.7 and 6.7 times more than transparent green, yellow, and transparent traps, respectively, or NaCl solution: 3.9, 7.6 and 6.2 times, respectively. Both ammonia and cow urine are attractive to N. parvus and may be tested to monitor the bugs in the field.

The presence of N. parvus is not easily detected in the field because these insects fly when disturbed making population survey difficult to conduct. A new monitoring method would be useful for estimating population density and detecting the presence of N. parvus in a particular area or on a specific host plant.
Cow urine has been proposed as attractant for stink bug species that are pests of soybean (Corrêa-Ferreira et al., 2003). Based on these captures, pest control measures can be implemented. Results of studies evaluating the responses of N. parvus to traps baited with cow urine and ammonia in the field are herein reported.

Material and Methods
Experiments were carried out in Londrina, state of Paraná, Brazil (23°19´S, 51°12´W). Traps consisted of 2-L plastic bottles in the following color pattern: transparent green, yellow, and transparent. Transparent and transparent green bottles were discarded PET containers. Yellow traps were the transparent bottles painted golden yellow. Bottles had four square openings (2 cm 2 ) and were placed 17 cm above the ground fixed to wooden stakes 5 m apart from a terrace with pigeon pea (Cajanus cajan L.) plants.
When experiments were installed, pigeon pea plants contained green and mature pods. The attractants (300 mL) were placed in the bottom of each bottle. In the first experiment (April 15, 2007) the attractants used were: tap water, NaCl 10% aqueous solution (w/v), and cow urine. In the second experiment (October 10, 2007), the same attractants were tested adding NH 4 OH 1% (w/v). Four replicates were set up and traps were maintained for three days in the field. Assessments were carried out three days after the installation of traps, when adult bugs were counted and removed.
Trials were set up on a randomized, complete block design. Distance between traps was 5 m within a block and 15 m between blocks. A two-way ANOVA was performed for the study of the interactions between trap colors and attractants followed by Tukey test (p < 0.05) to compare means (Tukey, 1949).

Results and Discussion
In the first experiment, significant effect of the factors attractant, trap color, and their interaction was observed (p < 0.05). Transparent green traps lured with cow urine caught 3.2 and 7.2 times more insects than yellow and transparent traps, respectively. Green traps lured with cow urine caught more insects than traps of the same color with just water or salt water, in which captures were negligible or did not occur (Table 1). In previous studies, green vessel water traps caught more male N. parvus than traps of other colors, except yellow. Yellow traps also caught more insects than blue, black, and silver traps (Ventura and Panizzi, 2004). A positive interaction between trap color and attractant was also reported for Diabrotica virgifera virgifera LeConte (Hesler and Sutter, 1993) and D. speciosa Germar (Arruda- Gatti et al., 2006).
In the second experiment, only attractant effect was significant (p < 0.05). Probably, the ammonia was so strong an attractant that the effects of color were made not significant. Traps lured with ammonia yielded 14.4, 4.7, and 6.7 more captures for transparent green, yellow, and transparent traps, respectively, than traps of the same color pattern carrying just water ( Table 2). The ammonia was a stronger attractant than urine, probably because higher concentration of active products in the ammonia in comparison to cow urine. Further investigations should address different ammonia concentrations for trapping N. parvus. Differently of the first experiment, cow urine was not attractive to N. parvus. Seasonal variation in the climatic conditions or physiological state of the bugs may be related to these conflicting responses.
Apparently, the attraction of N. parvus to cow urine and ammonia is related to protein alternative search by the insect. This behavior may occur in the absence of major hosts, i.e., leguminous plants (Schaefer, 1980;Schaefer and Mitchell, 1993). Adults and nymphs were found feeding on conspecific nymphs and adult cadavers (Ventura and Panizzi, 2004). These authors also reported that second instar nymphs deprived of leguminous seeds, fed exclusively on dead nymphs and reached the third instar, demonstrating the importance of the alternative food for N. parvus nutrition. This insect was  Agric. (Piracicaba, Braz.), v.67, n.1, p.84-86, January/February 2010 also found aggregated in groups of 30-40 adults, apparently feeding on dog feces and carrion after soybean harvest (Ventura and Panizzi, 2004).
Cannibalism and omnivory were also reported in other Alydidae. For instance, Megalotomus quinquespinosus (Say) was observed feeding on other adults when food plants were not available (Yonke and Medler, 1965). Megalotomus quinquespinosus adults together with Alydus eurinus (Say) were observed on decomposing animal and fecal matter (Yonke and Medler, 1968). Schaefer (1980) suggested that Alydidae are attracted to feces and carrion due to their water and concentrated semi liquid protein content. Additionally, their gregarious behavior and rapid movements (or locomotion) probably enable this type of exploration. Alydidae bugs produce rancid secretions (mostly shortchain fatty acids) from the metathoracic scent glands and noted that they are attracted to carrion and feces (Aldrich, 1995).
Ammonia is a by-product of protein decomposition and is known as attractant to other insects. For instance, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), was shown to be attracted by ammonia (Mazor et al., 1987). Attraction of Anastrepha spp. (Diptera: Tephritidae) to human urine and chicken feces also suggest attraction to ammonia (Piñero et al., 2003). The apple maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) was attracted by traps baited with ammonium carbonate (Yee et al., 2006). In conclusion, ammonia and cow urine could be used as attractants in traps for monitoring and detecting N. parvus in the field.