Gadi V. P. Reddy

Toxicological effects of pyrethroids on non-target aquatic insects

The toxicological effects of pyrethroids on non-target aquatic insects are mediated by several modes of entry of pyrethroids into aquatic ecosystems, as well as the toxicological characteristics of particular pyrethroids under field conditions. Toxicokinetics, movement across the integument of aquatic insects, and the toxicodynamics of pyrethroids are discussed, and their physiological, symptomatic and ecological effects evaluated. The relationship between pyrethroid toxicity and insecticide uptake is not fully defined. Based on laboratory and field data, it is likely that the susceptibility of aquatic insects (vector and non-vector) is related to biochemical and physiological constraints associated with life in aquatic ecosystems. Understanding factors that influence aquatic insects susceptibility to pyrethroids is critical for the effective and safe use of these compounds in areas adjacent to aquatic environments.

Laboratory and field efficacy of entomopathogenic fungi for the management of the sweetpotato weevil, Cylas formicarius (Coleoptera: Brentidae)

The sweetpotato weevil, Cylas formicarius (F.) (Coleoptera: Brentidae), is one of the most important pests of sweet potatoes in the world. With free trade between the United States and the U.S.-controlled Mariana Islands, C. formicarius has spread along with this commodity. Because of the cryptic nature of the larvae and nocturnal activity of the adults, and the cancellation of long-residual pesticides, this pest has become increasingly difficult to control. Therefore, the present study sought to explore and to compare the effectiveness of Metarhizium brunneum F52 (90ml a.i./ha), Beauveria bassiana GHA (40ml a.i./ha), spinosad (90g a.i./ha), azadirachtin (1484ml a.i./ha), B. bassiana+M. brunneum (20ml a.i./ha+45ml a.i./ha), B. bassiana+azadirachtin (20ml a.i./ha+742ml a.i./ha), B. bassiana+spinosad (20ml a.i./ha+45ml a.i./ha), M. brunneum+azadirachtin (45ml a.i./ha+742ml a.i./ha) and M. brunneum+spinosad (45ml a.i./ha+45 grams a.i./ha) in controlling this pest in both the laboratory and the field. The treatment with B. bassiana+M. brunneum was the most effective in reducing tuber damage by C. formicarius, producing the highest yields. The most adult cadavers were found in plots treated with the combination of two fungi. This combined fungal formulation appears to be appropriate for the practical control of C. formicarius on sweet potatoes.

Comparison of Thermal Performance Equations in Describing Temperature-Dependent Developmental Rates of Insects: (I) Empirical Models

Abstract Temperature greatly affects the developmental duration of insects at their different stages, and many mathematical models exist for describing their temperature-dependent developmental rates. It is important to choose a suitable model to predict outbreaks of pest insects under climate change. However, previous comparisons among these models were usually based on a single species. In the present study, we compared the six nonlinear models (the Briére-1, Briére-2, Lactin, Performance-2, beta, and Ratkowsky models) based on the goodness of fit and the trade-off between the models goodness of fit and structural complexity, using 10 temperaturedependent developmental rate datasets on insects to make the conclusions general. We found that the square root model (i.e., the Ratkowsky model) fitted all datasets well, and the curve shape produced by this model also approximates the curve shape of thermodynamically based mathematical models. The square root model was originally derived to be applicable to the growth rates of bacteria, and until now it has been generally ignored in entomology. We were mainly concerned with the predicted results obtained by using this model on observations of temperature-dependent developmental rates. We found that the square root model described well the pooled developmental rates in the low-, mid-, and high-temperature ranges, and we believe that it merits wider use in entomology.

Empirical model with excellent statistical properties for describing temperature-dependent developmental rates of insects and mites

Abstract Previous empirical models for describing the temperature-dependent development rates for insects include the Briére, Lactin, Beta, and Ratkowsky models. Another nonlinear regression model, not previously considered in population entomology, is the Lobry–Rosso–Flandrois model, the shape of which is very close to that of the Ratkowsky model in the suboptimal temperature range, but which has the added advantage that all four of its parameters have biological meaning. A consequence of this is that initial parameter estimates, needed for solving the nonlinear regression equations, are very easy to obtain. In addition, the model has excellent statistical properties, with the estimators of the parameters being “close-to-linear,” which means that the least squares estimators are close to being unbiased, normally distributed, minimum variance estimators. The model describes the pooled development rates very well throughout the entire biokinetic temperature range and deserves to become the empirical model of general use in this area.

Visual Cues Are Relevant in Behavioral Control Measures for Cosmopolites sordidus (Coleoptera: Curculionidae)

ABSTRACT Trap designs for banana root borer, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), have been done essentially on the understanding that C. sordidus rely primarily on chemical cues. Our present results indicate that these borers also rely on visual cues. Previous studies have demonstrated that among the eight differently colored traps tested in the field, brown traps were the most effective compared with the performances of yellow, red, gray, blue, black, white, and green traps; mahogany-brown was more effective than other shades of brown. In the current study, efficiency of ground traps with different colors was evaluated in the laboratory for the capture of C. sordidius. Response of C. sordidus to pheromone-baited ground traps of several different colors (used either individually or as 1:1 mixtures of two different colors) were compared with the standardized mahogany-brown traps. Traps with mahogany-brown mixed with different colors had no significant effect. In contrast, a laboratory color-choice tests indicated C. sordidus preferred black traps over other color traps, with no specific preferences for different shades of black. Here again, traps with black mixed with other colors (1:1) had no influence on the catches. Therefore, any other color that mixes with mahogany-brown or black does not cause color-specific dilution of attractiveness. By exploiting these results, it may be possible to produce efficacious trapping systems that could be used in a behavioral approach to banana root borer control.

Comparison of Thermal Performance Equations in Describing Temperature-Dependent Developmental Rates of Insects: (II) Two Thermodynamic Models

Abstract There are many descriptive statistical models describing the temperature-dependent developmental rates of insects without derivation of biophysical processes; thus, it is difficult to explain how temperature affects development from the thermodynamic mechanisms. Fortunately, two mathematical models (the Sharpe–Schoolfield–Ikemoto [SSI] model and Ratkowsky–Olley–Ross [ROR] model) based on thermodynamics have been built to explain temperature-dependent reaction rates. Despite their differences in construction, both models produce similar functions when used to describe the effect of temperature on the probability of a theoretical rate-controlling enzyme that is in its active state. However, the previous fitting method of the SSI model was unable to achieve global optimization of parameter estimates; that of the ROR model usually underestimates the maximal probability of the rate-controlling enzyme that is in its active state, as found in some empirical data sets. In the present study we improved the fitting methods for these two models. We then used these two models to fit 10 data sets from published references. We found the models based on the improved fitting methods agree with the empirical data well and predict that the maximal probabilities of the rate-controlling enzyme that is in its active state are close to 1. The SSI model produces a slightly better goodness-of-fit value for the model than the ROR model, whereas the latter predicts a more symmetrical curve for the probability of the rate-controlling enzyme that is in its active state. If thermodynamic parameters of two or more different species are to be compared, we recommend that researchers use one or the other of these two models and follow the same fitting methods for all species.

Integration of the predatory mite Neoseiulus californicus with petroleum spray oil treatments for control of Tetranychus marianae on eggplant

Abstract The red spider mite, Tetranychus marianae McGregor (Acari: Tetranychidae), a pest of several vegetable crops and perennials, is widespread in the Pacific Islands, like the Mariana Islands, where it was first reported. Recently, T. marianae has become a serious pest, particularly affecting eggplant. Efforts were therefore made to develop an integrated approach to control of T. marianae. First, indoor experiments on eggplant, Solanum melongena L. (Solanaceae), determined the optimal combination of petroleum spray oil (PSO; Volck® oil spray) with release of Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) for the management of T. marianae. Additionally, studies evaluated the viability of the predatory mites on Guam. The combination of N. californicus with PSOs produced significant control of T. marianae and did not affect the survival of N. californicus. Although dicofol and carbaryl reduced populations of T. marianae, they caused high mortality of N. californicus. Integrating PSO with N. californicus yielded better control of T. marianae than did N. californicus alone. The release of N. californicus at 200 individuals per plant reduced populations of T. marianae more than did other release rates. In addition, N. californicus was able to survive and become established after being released on Guam.

Efficacy of pheromone trapping of the sweetpotato weevil (Coleoptera: Brentidae): based on dose, septum age, attractive radius, and mass trapping.

ABSTRACT Pheromone dose, effective trapping distance, and longevity of the rubber septa loaded with sex pheromone of Cylas formicarius (F.) (Coleoptera: Brentidae) were evaluated for their impact on the efficacy of mass trapping of the insect in sweet potato fields in Guam in 2012–2013. The number of adults caught at different distances (10–100 m) was significantly different. Catches declined with increasing release distance from the trap in both downwind and upwind directions. While the maximum radius of attraction of pheromone-baited trap for C. formicarius in the field was 80 m, the effective distance for recapturing marked adults in the pheromone-baited Unitraps was 60 m. Pheromone lures were able to capture adults of C. formicarius after being stored in the laboratory for up to 98 d. The number of catches per trap per week was highest when lures were 0–14- and 15–28-d-old, and longer storage of septa led to a progressive reduction of catches. Pheromone traps baited with 100-µg lures captured significantly more adults compared with those loaded with 10-µg lures. In addition, effectiveness of pheromone trapping on damage to sweet potato was tested at two locations. Number of trapped adults, damage level at different times after trap installation, and yield production were evaluated. The number of C. formicarius adults collected in traps at both locations fluctuated dramatically among sampling dates and peaked on 13 September 2013, after which time the number of captures noticeably declined. This decrease was correlated to the increasing age and depletion of the pheromone lures. Pheromone traps significantly reduced feeding damage caused by weevils (<1 feeding hole per root in treatment; up to 38 feeding holes per root in the control) at both locations. Being consistent with damage levels, sweet potato yields in fields with traps were higher than those in untreated controls. We conclude that pheromone-baited traps are effective in reducing damage due to C. formicarius.

Bioactivity of Selected Eco-Friendly Pesticides Against Cylas formicarius (Coleoptera: Brentidae)

ABSTRACT Seven low risk pesticides including 1.2% azadirachtin (Azadirachta indica), extracts from Morinda citrifolia, petroleum oil 97%, Beauveria bassiana strain GHA, mixed essential oils (rosemary oil: 0.25%, peppermint oil: 0.25%, thyme oil: 0.25%, clove oil: 0.25% and other ingredients: 99.00%), spinosad and malathion, were evaluated against adults of the sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae) to determine potential insecticidal, repellent and feeding deterrence effects. Among the pesticides tested, A. indica and spinosad showed high insecticidal, repellent and feeding deterrence activity against C. formicarius. Spinosad, A. indica and malathion showed significantly higher insecticidal activity against C. formicarius. Similarly, these pesticides showed high repellency activity against adults, particularly 3–4 h after the treatment. The lowest food consumption was observed with the A. indica (0.8 g/adult/192 h), and the highest (9.9 g/adult/192 h) was with the petroleum oil spray. The other tested pesticides showed comparable activities. The chemicals we tested—particularly neem and spinosad—are therefore promising candidates as ecofriendly chemicals that could potentially replace broad-spectrum synthetic neurotoxins for control of C. formicarius.

Efficacy of Entomopathogenic Nematodes and Sprayable Polymer Gel Against Crucifer Flea Beetle (Coleoptera: Chrysomelidae) on Canola

Abstract The crucifer flea beetle, Phyllotreta cruciferae (Goeze), is a key pest of canola (Brassica napus L.) in the northern Great Plains of North America. The efficacies of entomopathogenic nematodes (Steinernema spp. and Heterorhabditis spp.), a sprayable polymer gel, and a combination of both were assessed on canola for flea beetle management. Plots were treated soon after colonization by adult flea beetles, when canola was in the cotyledon to one-leaf stage. Ten plants along a 3.6-m section of row were selected and rated at pre-treatment and 7 and 14 d post treatment using the damage-rating scheme advanced by the European Plant Protection Organization, where 1 = 0%, 2 = 2%, 3 = 5%, 4 = 10%, and 5 = 25% leaf area injury. Under moderate flea beetle feeding pressure (1–3.3% leaf area damaged), seeds treated with Gaucho 600 (Bayer CropScience LP Raleigh, NC) (imidacloprid) produced the highest yield (843.2 kg/ha). Meanwhile, Barricade (Barricade International, Inc. Hobe Sound, FL) (polymer gel; 1%) + Scanmask (BioLogic Company Inc, Willow Hill, PA) (Steinernema feltiae) resulted in the highest yields: 1020.8 kg/ha under high (2.0–5.3% leaf area damaged), and 670.2 kg/ha at extremely high (4.3–8.6 % leaf area damaged) feeding pressure. Our results suggest that Barricade (1%) + Scanmask (S. feltiae) can serve as an alternative to the conventional chemical seed treatment. Moreover, Scanmask (S. feltiae) can be used to complement the effects of seed treatment after its protection has run out.