Lloyd M. Dosdall

Diamondback Moth Ecology and Management: Problems, Progress, and Prospects

Agricultural intensification and greater production of Brassica vegetable and oilseed crops over the past two decades have increased the pest status of the diamondback moth (DBM), Plutella xylostella L., and it is now estimated to cost the world economy US

Biological control of the diamondback moth, Plutella xylostella: A review

4-5 billion annually. Our understanding of some fundamental aspects of DBM biology and ecology, particularly host plant relationships, tritrophic interactions, and migration, has improved considerably but knowledge of other aspects, e.g., its global distribution and relative abundance, remains surprisingly limited. Biological control still focuses almost exclusively on a few species of hymenopteran parasitoids. Although these can be remarkably effective, insecticides continue to form the basis of management; their inappropriate use disrupts parasitoids and has resulted in field resistance to all available products. Improved ecological understanding and the availability of a series of highly effective selective insecticides throughout the 1990s provided the basis for sustainable and economically viable integrated pest management (IPM) approaches. However, repeated reversion to scheduled insecticide applications has resulted in resistance to these and more recently introduced compounds and the breakdown of IPM programs. Proven technologies for the sustainable management of DBM currently exist, but overcoming the barriers to their sustained adoption remains an enormous challenge.

Resistance of some cultivated Brassicaceae to infestations by Plutella xylostella (Lepidoptera: Plutellidae).

Abstract The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most destructive cosmopolitan insect pests of brassicaceous crops. It was the first crop insect reported to be resistant to DDT and now, in many crucifer producing regions, it has shown significant resistance to almost every synthetic insecticide applied in the field. In certain parts of the world, economical production of crucifers has become almost impossible due to insecticidal control failures. Consequently, increased efforts worldwide have been undertaken to develop integrated pest management (IPM) programs, principally based on manipulation of its natural enemies. Although over 130 parasitoid species are known to attack various life stages of DBM, most control worldwide is achieved by relatively few hymenopteran species belonging to the ichneumonid genera Diadegma and Diadromus, the braconid genera Microplitis and Cotesia, and the eulophid genus Oomyzus. DBM populations native to different regions have genetic and biological differences, and specific parasitoid strains may be associated with the specific DBM strains. Therefore, accurate identification based on genetic studies of both host and parasitoid is of crucial importance to attaining successful control of DBM through inoculative or inundative releases. Although parasitoids of DBM larvae and pupae are currently its principal regulators, bacteria-derived products (e.g., crystal toxins from Bacillus thuringiensis) and myco-insecticides principally based on Zoophthora radicans and Beauveria bassiana are increasingly being applied or investigated for biological control. Viruses, nematodes and microsporidia also have potential as biopesticides for DBM. When an insect pest is exposed to more than one mortality factor, there is the possibility of interactions that can enhance, limit, or limit and enhance the various aspects of effectiveness of a particular control tactic. This paper reviews the effectiveness of various parasitoids and entomopathogens against DBM, interactions among them, and their possible integration into modern IPM programs.

Biology and Integrated Management of Wheat Stem Sawfly and the Need for Continuing Research

Abstract Selecting insect-resistant plant varieties is a key component of integrated management programs of oligophagous pests such as diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), but rigorous research on important life history parameters of P. xylostella in relation to host plant resistance is rare. We evaluated six conventional brassicaceous species, namely, Brassica napus L. ‘Q2’, B. rapa L., B. juncea (L.) Czern., B. carinata L., B. oleracea L., and Sinapis alba L., and two herbicide-tolerant cultivars, namely, B. napus ‘Liberty’ and B. napus ‘Conquest’ for their resistance against P. xylostella. Brassicaceae species and cultivars varied considerably in their susceptibilities as hosts for P. xylostella. Sinapis alba and B. rapa plants were highly preferred by ovipositing females and trichome density on adaxial and abaxial leaf surfaces had nonsignificant effects on P. xylostella oviposition. Larval survival was similar on the genotypes we tested, but host plants significantly affected larval and pupal developmental time, herbivory, pupal weight, silk weight, adult body weight, forewing area and longevity (without food) of both male and female P. xylostella. Larval and pupal development of females was fastest on B. juncea and S. alba, respectively. Specimens reared on B. napus Liberty and B. oleracea, respectively, produced the lightest female and male pupae. Defoliation by both female and male larvae was highest on B. rapa, whereas least herbivory occurred on S. alba. Females reared on S. alba were heavier and lived longer in the absence of food than their counterparts raised on other tested host plants. Brassica oleracea could not compensate for larval feeding to the level of the other species we evaluated. B. napus Conquest, B. napus Q2, B. carinata, B. rapa, and S. alba produced, respectively, 1.6-, 1.8-, 1.8-, 3.9-, and 5.5-fold heavier root systems when infested than their uninfested counterparts, suggesting that these species were better able to tolerate P. xylostella infestations.

Oviposition by Plutella xylostella (Lepidoptera: Plutellidae) and Effects of Phylloplane Waxiness

Abstract The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is historically one of the most important economic insect pests in the northern Great Plains of North America. Within this geographical region, the areas subjected to greatest attack are southern Alberta and Saskatchewan, southwestern Manitoba, eastern and northern Montana, North Dakota, northern South Dakota, and western Minnesota. Cumulative grain-yield losses and annual economic losses associated with this pest can exceed 30% and

Developmental Biology of the Cabbage Seedpod Weevil, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), in Spring Canola, Brassica napus, in Western Canada

350 million, respectively. Solid-stemmed cultivars of common wheat, Triticum aestivum L. (Poaceae), tolerant of infestation, are critical for C. cinctus management, but outbreaks of this pest continue to occur even after six decades of cultivar development. Furthermore, chemical control (a primary control option for other cereal (Poaceae) insect pests) has proven ineffective; this underscores the need to integrate resistant cultivars into a comprehensive integrated pest management program. We provide overviews of wheat stem sawfly biology, recent advances in applied research, the efficacy and integration of cultural and biological management strategies, and future directions for global research activities to manage wheat stem sawfly.

Using Degree-Day and Logistic Models to Predict Emergence Patterns and Seasonal Flights of the Cabbage Maggot and Seed Corn Maggot (Diptera: Anthomyiidae) in Canola

Abstract Three approaches were used to investigate effects of host plant epicuticular waxes on oviposition site selection by Plutella xylostella (L.). In the first approach, oviposition on canola (Brassica napus L.) that had epicuticular wax reduced by application of a carbamate herbicide (S-ethyl dipropylthiocarbamate) was compared with oviposition on untreated control plants. A second approach compared oviposition on sibling strains of B. napus with different wax blooms (glossy and waxy), and a third approach compared oviposition by P. xylostella on parafilm that had been applied to glossy and waxy B. napus strains for transfer of leaf components. Significantly more eggs were deposited on herbicide-treated plants (with reduced epicuticular wax) than on untreated controls. Similarly, more eggs were deposited on glossy than on waxy sibling strains of B. napus. In parafilm assays significantly more eggs were deposited on treated than on untreated parafilm. Several mechanisms could explain the differences in attractiveness of surfaces with varying wax content as oviposition sites for P. xylostella, including visual, chemical, and tactile differences between substrates. These mechanisms are discussed.

The Role of Ground Beetles (Coleoptera: Carabidae) in Weed Seed Consumption: A Review

Abstract Aspects of adult host plant preference and preimaginal development of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), were investigated in spring canola, Brassica napus L., in the Mixed Grassland Ecoregion of western Canada. In spring, overwintered adults initially occurred in high densities on volunteer canola and other brassicaceous weeds. In a mixed stand of Sinapis arvensis L., Thlaspi arvense L., and Descurainia sophia (L.) Webb, weevil numbers were significantly higher on S. arvensis than the other host plant species. Regardless of host plant species, adults were found more abundantly on inflorescences than on leaves or stems. Little adult migration to spring canola occurred when crops were in the seedling and rosette stages, but migration increased significantly to a maximum in the bud and flowering stages. Most oviposition occurred when plants were still flowering but pods on lower racemes were elongating. First instars were most abundant when seeds in lower pods were beginning to enlarge. The greatest abundance of second instars occurred when seeds within the lower siliques were fully enlarged. Third instars were most abundant when seeds in lower siliques were green. Development from egg to adult required 31–58 d in spring canola. Larvae occurred more abundantly on lower regions of racemes than on pods higher up. Although C. obstrictus is primarily a pest of autumn-seeded “winter” crops of B. napus in Europe and the northwestern United States, our study demonstrated that its preimaginal development occurred rapidly and successfully within the short-season “spring” crops of B. napus grown in western North America.

Glucosinolate profile and oviposition behavior in relation to the susceptibilities of Brassicaceae to the cabbage seedpod weevil

Abstract Seasonal flight activity periods and emergence phenologies of the cabbage maggot, Delia radicum L., and the seedcorn maggot, Delia platura (Meigen), were studied from 2002 to 2004 in canola, Brassica rapa L. and Brassica napus L., in central Alberta, Canada, in relation to degree-days and Julian-days. D. radicum was univoltine in canola. Peak emergence occurred after an accumulation of 345.8 ± 79.4 DD, and 50% flight activity required accumulation of 324.5 ± 46.8 DD (soil base 4°C). D. platura was bivoltine in canola. Peak emergence of the first generation required 339.5 DD, and the second generation required 594.5 ± 38.9 DD (soil base 3.9°C). Peak flight activity occurred after accumulation of 255.0 ± 74.2 and 639.9 ± 69.4 DD for the first and second generations, respectively. A logistic model was used to describe the relationship of degree-days and Julian-days with emergence patterns of adult flies and predicted that 10, 50, and 95% emergence of D. radicum required 213.7 ± 39.9, 324.5 ± 46.8, and 467.2 ± 46.3 DD, respectively. Logistic analysis predicted that 50% emergence of the first generation of D. platura required an average of 255.0 ± 74.2 DD, and the second generation required 526.8 ± 66.6, 639.9 ± 69.4, and 952.8 ± 77.0 DD for 10, 50, and 95% emergence, respectively. Determination of the temporal patterns of abundance of D. radicum and D. platura has potential application for pest management because it can help ensure that phenologies of candidate agents for biocontrol are synchronous with those of the pests they are targeted to control.

Spring Emergence Biology of the Cabbage Seedpod Weevil (Coleoptera: Curculionidae)

Abstract Weed management is a challenge in all agroecosystems. Given the negative consequences associated with herbicide-based weed management, it is important to consider integrated weed management options with emphasis on strategies such as biological control. Postdispersal weed seed predation by granivorous and omnivorous carabid beetles results in substantial natural suppression of weed populations. Although the role of ground beetles as “generalist predators” in various agroecosystems is known, their contribution to weed management is not well recognized. In this context, this review presents an account of carabids and their granivorous nature, the importance of a seed diet in the life histories of different carabid groups, factors affecting granivory, and their potential role in weed seed management. Below, we discuss the interrelationships among various factors influencing weed seed consumption by carabids, its consequences for weed management, and the need for future research.