Flight behaviour of European corn borer infected with Nosema pyrausta

The microsporidian Nosema pyrausta Paillot is a common and widespread pathogen of European corn borer, Ostrinia nubilalis (Hübner), in North America and Europe. Nosema negatively affects European corn borer longevity and fecundity. In this study, we used flight mills to examine the effects of Nosema infection on flight activity of unmated males and females at 1 and 3 days after pupal eclosion, taking the level of infection, as measured by number of Nosema spores per mg of tissue, into consideration. Nosema infection had a significant negative effect on distance, duration and speed of the longest uninterrupted flight, as well as on total distance and duration of flight of 1-day-old males, but not of 3-day-old males or females of either age. However, when insects with a light infection (\u3c15 spores/mg) were pooled with uninfected moths, significant negative effects of a moderate/heavy infection (≥15 spores/mg) were observed for most flight parameters in 1-day-old, but not 3-day-old, moths of both sexes. The magnitude of reduction was often substantial: e.g., distance and duration were sevenfold, and 3.5-fold less, respectively, in 1-day-old females with a moderate/heavy infection. Flight distance and duration were significantly negatively correlated with level of Nosema infection in 1-day-old, but not 3-day-old, moths of both sexes. The percentage of moths of either sex or age with a moderate/heavy Nosema infection flying given distances was less than that of lightly infected (\u3c15 spores/mg) moths. Among uninfected adults, forewing length was positively correlated with several measures of flight performance in males, but not females. However, some performance measures were correlated with wing length in females when infected with Nosema. Nosema infection was associated with reduced adult weight, but not forewing length, suggesting that negative effects of Nosema infection on flight performance are related to reduced energy reserves rather than smaller body size per se

Physiological status of overwintering boll weevils, Anthonomus grandis Boheman, in Arizona.

The overwintering physiology of boll weevils was evaluated using collections from a field in Laveen and 2 fields in Marana, Arizona, during the 1987-1988 winter and spring, and the 1988 non-cotton season, respectively. The objectives of the study were to determine if the strain of boll weevils, Anthonomus grandis Boheman, in Arizona enter true diapause, when diapause occurs, proportion of population entering diapause, and factors inducing diapause. Comparative studies were performed on 1987-1988 collections from both pheromone traps and bolls, to assess sex ratio, survival, reproductive behavior and adult longevity. Large numbers of weevils were caught in traps from September 1987 through April 1988, and there was no evidence of correlation of trap catches with prevailing temperatures. Hibernation cage studies also showed the absence of a sustained period of inactivity, and emergence was completed before the availability of squaring cotton. Significantly higher survival was observed among boll-enclosed weevils relative to the trap collected weevils, when placed in cages. Furthermore, moderate moisture was found to have a positive influence on survival. Studies on diapause and reproductive behavior revealed that a significant number of weevils in the trap collections was reproductive, whereas, a higher proportion of weevils collected from bolls seemed to be in a non-reproductive or diapausing condition. Subjecting weevil samples to three temperature/photographed regimes (25°C, 14L:10D; 20°C, 12L:12D; and 15°C, 10L:14D) showed that higher temperature/longer light cycle was more conducive to diapause completion and post diapause development. But, on transferring sub-samples to altered temperature/photoperiod regimes, temperature was determined to be the more important factor inducing diapause termination. Evaluations on longevity showed that 20°C 12L:12D photoperiod was optimal for survival of both fed and unfed weevils. Studies on weevil-samples collected from the two fields in Marana to evaluate the influence of plant phenology on overwintering status showed that the two populations were significantly different with respect to diapause status, reproductive behavior, egg lay, preoviposition period, moisture and fat content, and lipid composition. Higher proportions of weevils collected from the field with mature cotton bolls (Field 2) were found to be in a state of firm diapause, whereas those from a field with all stages of fruiting cotton (Field 1) were predominantly reproductive or intermediate

Management of Pyrethoid-Resistant Whiteflies in Arizona Cotton: Selection, Cross-Resistance, and Dynamics

In 1995, silverleaf whitefly, Bemisia argentifolii Bellows and Perring, resistance to the widely -used mixture of Danitol® (fenpropathrin) + Orthene® (acephate) was shown to be severe and widespread in Central Arizona cotton. Thereafter, laboratory experiments were undertaken to identify the other major insecticides that were affected by this resistance. Whiteflies were collected in November of 1995 from Maricopa (highly resistant) and Yuma (relatively susceptible) County locations in Arizona. A composite colony was established by combining Yuma and Maricopa whiteflies in a 4:1 ratio. After six generations of adult selection of this population with Danitol + Orthene, appreciable shifts in the concentration responses for pyrethroid, organophosphate, and carbamate insecticides were observed, indicating heritable variation for resistance in the source populations. From this we obtained definitive proof that resistance to Danitol + Orthene confers cross-resistance to Asana® (esfenvalerate), Capture® (bifenthrin), Danitol, Decis® (deltamethrin), Decis + Orthene, and Karate® (lambda-cyhalothrin). Additionally, selection with Danitol + Orthene resulted in statistically significant reductions in susceptibility to Curacron® (profenofos), Lannate® (methomyl), Monitor® (methamidaphos), and Ovasyn® (amitraz). Studies were performed to assess tolerance of Maricopa (pyrethroid- resistant) and Yuma (pyrethroid-susceptible) populations to a diversity of conventional insecticides currently registered for use in Arizona cotton, with the intention of finding compounds that showed promise for overcoming pyrethroid resistance. Of the materials evaluated, Curacron, Lannate, Lorsban® (chlorpyrifos), Ovasyn, Supracide® (methidathion), and Vydate® (oxamyl) were most promising. To determine to what degree pyrethroid resistance in cotton influenced resistance in winter vegetables and melons, and vice versa, whitefly populations were collected from a succession of these crops in Western and Central Arizona regions. In most instances, the whiteflies in Western Arizona were significantly more susceptible to Danitol + Orthene than those in Central Arizona. Significant decreases were found in susceptibility to Danitol + Orthene during the 1996 season at three of the four locations in which multiple crops were monitored. This emphasizes that pyrethroid resistance levels can be increased in whitefly populations from any of the cotton, melons, or other winter vegetable crops evaluated. Therefore, management of pyrethroid resistance in Arizona cotton will require harmonizing resistance management efforts and specifically limiting pyrethroid use in the entire crop complex

Susceptibility of Field Populations of Pink Bollworm (Lepidoptera: Gelechiidae) to Azinphosmethyl and Permethrin

Responses of five field -collected populations of the pink bollworm. Pectinophora gossypiella (Saunders). from Arizona and southern California. were compared with those of a standard. susceptible -laboratory strain. Field strains showed less than twofold difference in response to azinphosmethyl at LD₅₀ but had variable levels (1.3- to 18.3-fold) of response to permethrin. Strains from Yuma and Phoenix (Arizona) and Westmoreland (California) had highest levels of resistance to permethrin

Reversion of Permethrin Resistance in Field Strains and Selection for Azinphosmethyl and Permethrin Resistance in Pink Bollworm (Lepidoptera: Gelechiidae)

Rearing of two field strains (Maratha, Yuma) of pink bollworm. Pectinophora gossypiella (Saunders). from Arizona under conditions free of insecticides resulted in reversion of resistance (in adults) in four and five generations. respectively. to levels close to that found in the susceptible laboratory strain. Permethrin resistance in these field strains is unstable and is apparently in its early phase of development. Results suggest that monitoring of pink bollworm resistance in field strains reared in the laboratory should be performed in the F₁ generation. Subsequent selection studies were performed on both larval and adult stages to investigate the capacity of the pink bollworm to develop resistance in both life stages. Fourteen generations of selection of larvae and adults with azinphosmethyl produced 1.9- and 1.6-fold tolerance. respectively. in the adult stage. Sixteen generations of larval selection with permethrin generated 9.7-fold resistance in adults. while 14 generations of adult selection produced 8.8-fold resistance in adults. Azinphosmethyl evidently possesses a low degree of selectivity for development of resistance in pink bollworm adults. Selection of larvae with both azinphosmethyl and permethrin seemed to generate higher levels of tolerance in larvae than in adults

Reversion of Permethrin Resistance in Field Strains and Selection for Azinphosmethyl and Permethrin Resistance in Pink Bollworm (Lepidoptera: Gelechiidae)

Rearing of two field strains (Maratha, Yuma) of pink bollworm. Pectinophora gossypiella (Saunders). from Arizona under conditions free of insecticides resulted in reversion of resistance (in adults) in four and five generations. respectively. to levels close to that found in the susceptible laboratory strain. Permethrin resistance in these field strains is unstable and is apparently in its early phase of development. Results suggest that monitoring of pink bollworm resistance in field strains reared in the laboratory should be performed in the F₁ generation. Subsequent selection studies were performed on both larval and adult stages to investigate the capacity of the pink bollworm to develop resistance in both life stages. Fourteen generations of selection of larvae and adults with azinphosmethyl produced 1.9- and 1.6-fold tolerance. respectively. in the adult stage. Sixteen generations of larval selection with permethrin generated 9.7-fold resistance in adults. while 14 generations of adult selection produced 8.8-fold resistance in adults. Azinphosmethyl evidently possesses a low degree of selectivity for development of resistance in pink bollworm adults. Selection of larvae with both azinphosmethyl and permethrin seemed to generate higher levels of tolerance in larvae than in adults