Lucas E. Cazado

First Record of Helicoverpa armigera (Lepidoptera: Noctuidae) in Argentina

Summary Because of the recent presence of Helicoverpa armigera in Brazil and Paraguay in 2013, pheromone traps were deployed in chickpea crops at 2 localities in Tucumán province to determine if this noctuid was present in Argentina. This pest was detected at both locations, confirming the presence of H. armigera in Argentina for first time.

Determination of Number of Instars of Rhyssomatus subtilis (Coleoptera: Curculionidae) Based on Head Capsule Widths

Abstract Rhyssomatus subtilis Fiedler (Coleoptera: Curculionidae) is an important pest of the soybean crop in northwestern Argentina. Few studies have been made on specific parameters of its life history and ecology. The aim of this study was to determine the number of larval stages of R. subtilis. One thousand and eighteen larvae were collected from soybean plants during 2 yr (2011 and 2013), and head capsule width of each larva was measured. For analysis of data, the Hcap program and Dyars rule were used. The Hcap program showed 4 different peaks in the frequency distribution of the head capsule widths. This result also agreed with Dyars rule that revealed a perfect geometric larval growth pattern for each instar by regression analysis. The excellent fit to a linear model, indicates that no instar was overlooked. This research identified 4 instars for R. subtilis.

Species From the Heliothinae Complex (Lepidoptera: Noctuidae) in Tucumán, Argentina, an Update of Geographical Distribution of Helicoverpa armigera

The Heliothinae complex in Argentina encompasses Helicoverpa gelotopoeon (Dyar), Helicoverpa zea (Boddie), Helicoverpa armigera (Hübner), and Chloridea virescens (Fabricius). In Tucumán, the native species H. gelotopoeon is one of the most voracious soybean pests and also affects cotton and chickpea, even more in soybean-chickpea succession cropping systems. Differentiation of the Heliothinae complex in the egg, larva, and pupa stages is difficult. Therefore, the observation of the adult wing pattern design and male genitalia is useful to differentiate species. The objective of this study was to identify the species of the Heliothinae complex, determine population fluctuations of the Heliothinae complex in soybean and chickpea crops using male moths collected in pheromone traps in Tucuman province, and update the geographical distribution of H. armigera in Argentina. The species found were H. gelotopoeon, H. armigera, H. zea, and C. virescens. Regardless of province, county, crop, and year, the predominant species was H. gelotopoeon. Considering the population dynamics of H. gelotopoeon and H. armigera in chickpea and soybean crops, H. gelotopoeon was the most abundant species in both crops, in all years sampled, and the differences registered were significant. On the other hand, according to the Sistema Nacional Argentino de Vigilancia y Monitoreo de Plagas (SINAVIMO) database and our collections, H. armigera was recorded in eight provinces and 20 counties of Argentina, and its larvae were found on soybean, chickpea, sunflower crops and spiny plumeless thistle (Carduus acanthoides). This is the first report of H. armigera in sunflower and spiny plumeless thistle in Argentina.

Geographical distribution and new host associations of Rhyssomatus subtilis (Coleoptera: Curculionidae) Northwestern in Argentina.

SUMMARY Rhyssomatus subtilis, the black soybean weevil, has emerged as a major pest of soybean [Glycine max (L.) Merr. (Fabales: Fabaceae)] in northwestern Argentina during the last 3 yr. This species was detected in 30 localities of Salta, Santiago del Estero and Tucumán provinces comprising a total area of about 541,000 ha. This species was observed for the first time developing on dry bean [Phaseolus vulgaris L. (Fabales: Fabaceae)] crops and feeding on 3 unrelated weeds [Conyza bonariensis (L.) Cronquist (Asterales: Asteraceae), Brassica campestris (L.) Metzg. (Brassicales: Brassicaceae) and Sphaeralcea bonariensis (Cav.) Griseb (Malvales: Malvaceae)]. The damage produced by R. subtilis in dry bean crops is similar to that produced in soybean crops. The results obtained suggest that as of 2012, R. subtilis has greatly expanded its distribution since its first detection in 2006 and produces major direct and indirect damage in soybean and dry bean crops in northwestern Argentina.

Rhyssomatus subtilis (Coleoptera: Curculionidae) Impact in Soybean Plant Stands

Abstract  The black soybean weevil, Rhyssomatus subtilis (Fiedler), is an important but infrequently studied insect pest of soybean, Glycine max (L.) Merrill, in South America. Severe crop damage occurs when the adult weevils attack soybean seedlings, resulting in reduced plant stands, and when weevils feed on and oviposit in seedpods. The objectives of this 3-yr study were to quantify early-season damage caused by R. subtilis to terminal buds and plant stands in soybean and evaluate insecticide seed treatments under field conditions relative to this damage. Terminal bud damage is the most consistent criteria for determining early-season damage by R. subtilis to soybean. The results indicated that R. subtilis can cause as much as 36% plant stand loss in soybean. Thiamethoxam and a mixture of ethiprole + fipronil provided significant levels of control of R. subtilis damage, with the higher doses of each product tending to provide longer-lasting protection.

Head Capsule Width is Useful for Determining Larval Instar in Heilipus lauri (Coleoptera: Curculionidae)

Summary The purpose of this study was to determine the number of larval instars for Heilipus lauri Boheman (Coleoptera: Curculionidae). We reared 385 larvae under laboratory conditions and measured the width of the larval head capsules from digital images. Data were analyzed using the Hcap program and Dyars rule. Analysis of the frequency distribution showed the existence of 4 distinct peaks. The mean Dyars constant was 1.42, where the relationship between the natural logarithm of the head capsule widths and the number of larval instars resulted in a near-perfect geometric growth for each instar. The excellent fit of the data to a linear model suggests that there was nearly no overlap among the 4 instars in the head capsule measurements, making it possible to distinguish the 4 instars of H. lauri accurately.

Sexual dimorphism of Rhyssomatus subtilis (Coleoptera: Curculionidae)

Abstract Examination with a binocular microscope of adults of Rhyssomatus subtilis Fielder (Coleoptera: Curculionidae) revealed distinct differences between the sexes in the foreleg, which permits their differentiation with complete accuracy. In the female the profemual process is weak, subacute, angulate and the protibia has an uncus and mucro. In the male the profemur process is strong, curved, subacute, tooth-like and lacks an protibia uncus.