Peter C Ellsworth

PMID: 12216807;Abstract:

Studies were conducted in 1994 and 1995 to examine the effects of a range of action thresholds for managing Bemisia tabaci (Gennadius) Biotype B (= B. argentifolii Bellows & Perring) with insecticides in cotton on populations of arthropod predators in Imperial Valley, CA, and Maricopa, AZ. Application of insecticides significantly reduced population densities of spiders, Geocoris punctipes (Say), G. pallens (Stål), Orius tristicolor (White), Nabis alternatus Parshley, Zelus renardii Kolenati, Hippodamia convergens Guerin-Méneville, Spanogonicus albofasciatus (Reuter), Drapetis sp., and Chrysoperla carnea Stephens in one or both years and sites compared with untreated controls. Use of higher B. tabaci thresholds conserved some species and groups relative to lower thresholds. Stepwise regression analyses indicated that reductions in predator populations were generally influenced more strongly by the timing of the first insecticide application than by the total number of sprays necessary to maintain suppression of the pest below any given action threshold. A predation index, which weights the importance of each predator species based on their known frequency of predation on B. tabaci and another key pest, Pectinophora gossypiella (Saunders), was developed and analyzed. Patterns were similar to results based on changes in abundance alone, but the index generally revealed less severe effects of insecticides on overall predator function. The current action threshold for conventional insecticidal control of B. tabaci in Arizona and southern California is five adults per leaf. Results here suggest that predator conservation may be enhanced by raising the initial threshold to delay the first application or initially using more selective materials such as insect growth regulators.

Abstract:

Climatic matching and pre-release performance evaluation were useful predictors of parasitoid establishment in a retrospective analysis of a classical biological control program against Bemisia tabaci biotype "B" in the USA. Laboratory evaluation of 19 imported and two indigenous parasitoid species in quarantine on B. tabaci showed that the Old World Eretmocerus spp, had the highest attack rate. The climate matching program CLIMEX was used to analyze the establishment patterns of five Old World Eretmocerus spp. introduced to the Western USA. The top matches ±10% for the climate of the area of introduction and origin of the introduced parasitoids always included the species that established. The Old World Eretmocerus spp. came from regions characterized by many separate biotypes of B. tabaci other than "B," but are considered specialists of the B. tabaci complex as compared to the indigenous North American oligophagous Eretmocerus spp. This narrower host range and high attack rate combined with climatic adaptation may account for their establishment in the USA. A set of predictive tools and guidelines were used to select the best candidate for importation and possible release into Australia that has been recently invaded by the "B" biotype. The establishment patterns of the introduced Eretmocerus spp. and a comparison of climates of their respective locations in the USA were compared with the affected area in Australia. The best climatic match was the Lower Rio Grande Valley of Texas suggesting its dominant parasitoid, E. hayati ex. Pakistan be considered as the first candidate for evaluation as a biological control agent.

Abstract:

A general description of the life stages of Chelonus sp. nr. curvimaculatus, an egg-larval parasitoid of pink bollworm, Pectinophora gossypiella (Saunders), is presented. Pink bollworms were reared in the laboratory on a wheat germ diet. At 29°C, parasitoid eggs (0.12-0.18 mm) begin to eclose ∼22 h after oviposition. Three instars occur in this species. The 1st instar is endoparasitic and ranged in length from 0.14 mm (neonate) to 1.25 mm (∼9 d old. end of the 1st stadium). The 2nd instar also is endoparasitic and is 1.89-3.04 mm long. This stadium lasts ∼2-3 d. The 3rd instar is an average of 3.82 mm long and is endoparasitic early in its development but becomes ectoparasitic toward the completion of its development. This stadium lasts ∼3 d. The pupal stage lasts ∼6-7 d. Adult parasitoids begin to emerge ∼21 d after oviposition. Parasitized and unparasitized pink bollworm larvae deceloped through 4 stadia. Larval head capsule widths. body lengths, and weights of parasitized pink bollworms are significantly smaller than those of unparasitized larvae during the 3rd and 4th stadia. Parasitized 4th-instar pink bollworms have a mean head width of 0.8687 mm, body length of 6.28 mm, and weight of 6.9 mg. Fourth-instar unparasitized pink bollworm measurements were 1.0743 mm, 9.31 mm, and 17.7 mg, respectively.

Abstract:

Detailed biological information is lacking on Chelonus sp. nr. curvimaculatus, an egg-larval parasitoid of Pectinophora gossypiella (Saunders). We conducted laboratory studies to gain new understanding of the biology of C. sp. nr. curvimaculatus reared on this economically important host. Developmental time, adult longevity, and fecundity of C. sp. nr. curvimaculatus were studied under 5 constant temperatures and 3 photoperiods. At 20°C, parasitoid development, from egg to adult, was longer for females (53.6 d) than for males (49.5 d), but at 35°C both sexes developed in a similar period (19.9 d for females and 18.8 d for males). The thermal constant for female and male C. sp. nr. curvimaculatus, from egg to adult, was 366 and 353 above a base temperature of 12,95°C and 12.47°C, respectively. Adult male (≈16.5 d) and female (≈20 d) parasitoids lived longest at 20°C, and at 35°C both lived ≈6.5 d. True and realized fecundity was highest at 25°C (≈1,034 and 420 eggs per female, respectively) and lowest at 35°C (≈119 and 67, respectively). The percentage of superparasitized host eggs was greatest at 25 and 30°C (≈55%), and lowest at 35°C (≈29%). Net reproductive rates (Ro) were variable across all conditions. Based on the realized fecundity, Ro was highest at 20°C (103.37) and lowest at 35°C (32.79). Temperature and the age of the parasitoid had the greatest influence on fecundity. Photoperiod played a minor role in influencing developmental rates, but not adult longevity or fecundity of C. sp. nr. curvimaculatus. This life history and rearing information should be useful in field release studies and the development of future biological control programs for pink bollworm.

Abstract:

This study examined the impact of irrigation water on certain aspects of an insect-plant relationship in the field including the assessment of plant-mediated water effects on an herbivore's development, survival, and behavior, and plant damage parameters and host tissue water status. Maize (Zea mays L.) plants were arranged in a randomized complete block design in the field over two years in North Carolina (NC). Four blocks were subjected to three different irrigation treatments initiated ca. one week before anthesis: optimal, intermediate, deficit water supply. Each plant was infested with one (1986) or two (1987) black head stage, E-race European corn borer [Ostrinia nubilalis (Hübn.)] (ECB) egg masses at tasselling. ECB development, tunnelling site, and survival as well as plant tissue water status (tissue % water contents [θ] & leaf water potentials [Ψ]) were recorded through July. The irrigation effect on ECB parameters was slight and variable. Internal stalk temperatures of optimal plants were consistently cooler than their deficit counterparts (1 day-degree/day). With degree-days included as an explanatory variable in the analyses, there were no significant irrigation effects on the ECB parameters, except for total proportion of ECB's bored into maize plant parts. More ECB's bored into drier plants than in optimal plants; however, this trend was not significant in 1987. Plant water indices showed that though Ψ responded to irrigation, there were only minor changes in tissue θ, particularly in view of the larger diurnal tissue changes observed and the relatively high, sustained stalk θ levels seen over all treatments. Examination of ECB pupal θ confirmed that dietary water changes were minor or non-limiting to the insects' developmental physiology, because pupal θ was not sensitive to the irrigation treatments. Though water supply changes have drastic developmental and agronomic consequences for the maize plant, little or no changes were seen in the ECB feeding environment. Furthermore, a plant damage model was developed whereby the total % of ECB's tunnelled into maize was related to the mean larval age. The implications of this model on the understanding of ECB tunnelling behavior, damage potential, and pest management is noted. © 1992 Kluwer Academic Publishers.