Eduardo Willink

Toxic effects of lemon peel constituents on Ceratitis capitata

A series of experiments were conducted to evaluate the toxicity of lemon peel extracts incorporated into mediterranean fruit fly Ceratitis capitata diet. Extracts were obtained with different solvents: diethyl ether, ethyl acetate, and methanol. All three extracts were toxic to some extent; the diethyl ether extract was selected for further studies. Ether extracts of lemon peel were prepared weekly over a 2-month period, from fruits collected on the 1st d of the bioassay. Weekly GC-MS and UV analyses of the extracts demonstrated that the concentration of citral and coumarins decreased in the peel after harvest. We conducted a series of bioassays to evaluate the toxicity of the ether extract, and mixtures of this extract with citral, 5,7-dimethoxycoumarin, and linalool incorporated to C. capitata larvaes natural diet (lemon slices endocarp) at a concentration of 250 μg/g of diet. Significant larvicidal activity can be obtained from a fresh lemon peel extract; however, when the extract was obtained from stored lemons, toxicity decreased. Addition of small amounts of citral or 5,7-dimethoxy- coumarin, and linalool to the stored lemon peel extract would bring back the toxicity to the rates of fresh lemons extracts. Finally, female adults of C. capitata fed on diets containing additional amounts of ether extract, 5,7-dimethoxycoumarin, and linalool, were exposed to different photoperiods to test for phototoxicity. The treatment was toxic and affected the oviposition capacity of females depending on photoperiod.

DEMOGRAPHIC AND QUALITY CONTROL PARAMETERS OF ANASTREPHA FRATERCULUS (DIPTERA: TEPHRITIDAE) MAINTAINED UNDER ARTIFICIAL REARING

Abstract The integration of the sterile insect technique (SIT) in the management of the South American fruit fly Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) is a promising alternative to chemically-based control in those areas where it is sympatric with Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) or other tephritid species for which the SIT is being used. Implementation of the SIT requires the development of a cost effective mass-rearing protocol. In this work, we present demographic and quality control parameters for the A. fraterculus strain reared at the Estación Experimental Agroindustrial Obispo Colombres, Tucumán, Argentina. Considering the rearing cage as the reproduction unit, we observed that fecundity is optimal during the first 3 weeks after the onset of oviposition. Fertility was constant during this period. During 2003 and 2004, some improvements were made to the existing rearing protocol, which resulted in increased larval viability, pupal weight, and adult emergence. Current weekly egg production is 1 million per week. These eggs are used to maintain the colony and to assess quality parameters. Finally, research needs leading to improved yields and fly quality are discussed.

COMPATIBILITY AND COMPETITIVENESS OF A LABORATORY STRAIN OF ANASTREPHA FRATERCULUS (DIPTERA: TEPHRITIDAE) AFTER IRRADIATION TREATMENT

Abstract We evaluated under semi-natural field cage conditions sexual compatibility and competitiveness of a laboratory strain (LAB) compared to a wild population (TUC) of Anastrepha fraterculus (Wiedemann). The LAB strain is produced under semi-mass rearing conditions at the Estación Experimental Agroindustrial Obispo Colombres facility (Tucumán, Argentina). Wild flies were obtained at Horco Molle (Tucumán, Argentina) from infested guava fruits. LAB pupae were irradiated (60Co) 48 h before adult emergence. The tested doses were 0 (control), 40, 70, and 100 Gy. Twenty-five males and 25 females each of TUC and LAB were released into cages and mating pairs collected. Only 1 irradiation dose was considered at a time. Females were separated and allowed to lay eggs into artificial fruits to estimate induced sterility from the corresponding hatching rate. Copulation start time did not differ significantly between strains nor among irradiation treatments. Copulation duration showed highly significant differences among irradiation doses, but no differences between strains. The index of sexual isolation (ISI) and the relative sterility index (RSI) indices indicated that LAB and TUC are fully compatible, males from TUC and LAB did not differ in mating competitiveness, and irradiation within the range tested did not affect these indices. Non-irradiated LAB females exhibited higher mating propensity than TUC ones. However, a significant reduction in the female relative performance index (FRPI) index was observed with increasing irradiation dose. The analysis of induced sterility indicated that treatment with 40 Gy reduces male fertility from about 80% to 0.75%, and higher doses produce total sterility. In females, the 40 Gy dose reduces fertility to about 2% and higher doses prevent egg laying.

Induction of Sterility in Anastrepha fraterculus (Diptera: Tephritidae) by Gamma Radiation

Abstract In relation to the application of the sterile insect technique (SIT) for the South American fruit fly Anastrepha fraterculus (Wiedemann), we analyzed the effect on adult fertility of different doses of gamma irradiation and the age of pupae at the time of irradiation. In a first experiment, we applied doses of 50, 70, and 90 Gy to pupae at 24, 48, 72, and 96 h before adult emergence. In a second experiment we irradiated pupae 48 h before emergence with 20, 40, and 60 Gy and estimated male and female fertility and sperm transfer by irradiated males. The results indicated pupal age at irradiation does not significantly affect male fertility. If males irradiated with 60 Gy are crossed to non-irradiated females the fertility is about 1%. Females irradiated with 40 Gy did not lay eggs independently of the male to which they mated. No significant effects of radiation were observed with respect to the ability of males to transfer sperm. A dose of 70 Gy applied 48 h before adult emergence induces 100% sterility in both males and females.

Multiple mating in Anastrepha fraterculus females and its relationship with fecundity and fertility

The occurrence of female remating has been widely reported in insects and the frequency at which it occurs and the factors driving females’ remating behavior have been shown to be both species specific and variable within species. Herein, we studied the remating behavior of females from a well established laboratory colony and a wild population of the South American fruit fly, Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae), under laboratory conditions. Latency to first mating (number of days from the onset of the experiment until the first copula) was shorter for remating females than for females that did not remate. Two‐day fecundity was higher for females that did remate than for monogamous females. Egg hatch was sustained after remating and was not affected by the number of times the female mated. However, when females willing to remate were prevented from doing so, percent egg hatch showed a significant drop. These results and the fact that remating occurred more often in more fecund females than in less fecund ones suggest that remating may be a response to sperm depletion. Remating frequency was similar in laboratory and wild flies, but 2‐day fecundity was higher for laboratory than for wild females of similar mating status. Also, the length of the refractory period (time between first and second copulation) was longer for wild than for laboratory females. Differences between strains could be the result of artificial selection. Results are discussed from a theoretical and applied perspective in the context of direct benefits to females.

Fruit compounds affect male sexual success in the South American fruit fly, Anastrepha fraterculus (Diptera: Tephritidae)

Although exposure to plants has been shown to influence sexual behaviour in a number of phytophagous insect species, a relatively small number of fruit flies have been investigated in that respect. Here, we evaluated the effect of exposure to the pulp of guava and mango and to essential oils emanating from glands in the flavedo area of lemons on the mating success of Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) males. We also evaluated different durations of exposure and the need for physical contact with the fruit. Results showed that exposure to guava increased the mating success of both wild and laboratory males relative to non‐exposed males. In addition, exposed wild flies copulated earlier than non‐exposed males. Physical contact with the fruit or ingestion of compounds was not a prerequisite for this phenomenon to occur, since just the exposure to volatiles resulted in a significant enhancement in mating success. Exposure to mango did not affect male sexual performance. In contrast, exposure to lemon for 1 day decreased mating success of males relative to unexposed males, whereas exposure for longer periods seemed to eliminate this effect resulting in comparable mating success rates between treated and untreated males. These results provide a better understanding of the sexual behaviour of this species and may also find application for its control.

Genetic characterization of fall armyworm (Lepidoptera: Noctuidae) host strains in Argentina.

ABSTRACT Fall armyworm is a major economic pest throughout the Western Hemisphere. Previous studies of populations in the southern United States, Brazil, and the Caribbean demonstrated the existence of two morphologically identical but genetically distinct host strains that can only be distinguished using genetic markers, including polymorphisms in the mitochondrial Cytochrome Oxidase I (COI) gene and in the Z-chromosome linked Triose phosphate isomerase (Tpi) gene. The strains differ in some physiological and behavioral characteristics, most notably their preference for different plant hosts, but are capable of hybridizing in the laboratory and in the field. These traits suggest that the strains are in the process of divergence, which may or may not be hemispheric in scope. The objective of this study was to determine whether the two strains are present in Argentina. It was found that the strain-diagnostic haplotypes of the COI and Tpi genes subdivided the Argentina population into two major groups. Each group displayed biases in their distribution among different host plants that were generally consistent with expected strain behavior. The overall results indicated that Argentina fall armyworm exhibit similar genetics and behavior to populations in the rest of the hemisphere. In addition, the Argentina populations had comparable haplotype frequencies to those from Brazil and Texas, consistent with possible interactions with these fall armyworm groups, but appeared to have had minimal exchanges with those from Puerto Rico or Florida.

Effects of p-Vinylphenyl Glycosides and Other Related Compounds on the Oviposition Behavior of Ceratitis capitata

Elaphoside-A [p-vinylphenyl (β-d-glucopyranosyl)-(1→3)-β-d-allopyranoside], a Mediterranean fruit fly oviposition deterrent, was previously isolated from an Argentine collection of the fern Elaphoglossum piloselloides. In order to establish the structural requirements for the observed oviposition inhibition, we synthesized and characterized 4 known and 21 new aromatic glycosides structurally related to elaphoside-A. Their effects on the oviposition behavior of Ceratitis capitata females are discussed.

Development of a larval diet for the South American fruit fly Anastrepha fraterculus (Diptera: Tephritidae)

Mass-rearing protocols must be developed, in particular, a cost-effective larval diet, to implement the sterile insect technique against Anastrepha fraterculus (Wiedemann). The key elements of this diet are the optimal nutrients and their concentrations, diet supports or bulking agents, and the pH of the diet. To improve the currently used formulation and develop a more cost-effective diet, in the present study, we evaluated various supports, sugar contents, nutrient proportions and pH levels. Egg-to-pupa recovery was found to increase when agar was replaced with sponge cloth in the diet. Although low, the recovery values obtained when using the sugarcane bagasse-based diet were similar to those obtained when using the agar-based diet, but the percentage of adult emergence was lower. Larval viability was found to increase when the amount of sugar in the diet was doubled. Yet, it is still necessary to evaluate this diet on a larger scale and determine the feasibility of reusing the sponge cloth to reduce the costs of larval diets.

Preference and Performance of Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) on Three Citrus Hosts: Laboratory and Field Assessment

Abstract The relationship between preference and performance is crucial to the ecology and evolution of plant–insect interactions. Oviposition preference and offspring performance were evaluated for a citrus pest, the leafminer Phyllocnistis citrella (Lepidoptera: Gracillariidae), on three of its host plants: lemon (Citrus limon L. Burm.), orange (Citrus sinensis L. Osbeck), and grapefruit (Citrus paradisi Macfadyen) in Tucumán province (northwest Argentina). Choice and no-choice tests were performed in open and enclosed environments, and performance parameters (development time, survival, pupal size, and sex ratio) were estimated from laboratory rearing and 3-yr field sampling data. Parasitism rates were studied in laboratory choice test and field assessments. Preference trends were inconsistent, with lemon receiving more eggs in some tests, whereas no preference was observed in others. Patterns of host use in the field did not show significant differences among species. Leafminer performance, including parasitism and predation rates, was generally homogeneous among host plants. From these results, lemon, orange, and grapefruit seem to represent intrinsically similar resources for P. citrella populations in northwest Argentina, a trend that was accompanied by a lack of consistent oviposition preferences in foraging females. Ecological conditions might be more important than physiological adaptation in shaping a probably labile host ranking in this pest species.