Mortality of heliothis zea eggs : affected by predator species, oviposition sites, and rain and wind dislodgement

Abstract

Predation rates of Heliothis zea (Boddie) (Lepidoptera: Noctuidae) eggs located on cotton plants were determined by placing ³²P labelled H. Zea eggs on different plant structures throughout the plants. Egg predation averaged 81.7, 81.4, and 57.7% during the summers of 1982, 1983, and 1984. Predation averaged 27.9% for sucking predators and 5.1% for chewing predators. Orius tristicolor (White), O. insidiosus (Say), Geocoris punctipes (Say), Pseudatomoscelis seriatus (Reuter), and Solenopsis invicta Buren contributed ca. 86% of the predation attributable to specific arthropods. A minor trend for predation over the three years was for slightly higher predation rates towards the tops of plants. Predation rates decreased each year as the season progressed from 81.8 to 100% in pre-squaring cotton, to 55 to 80% at first hard-boll stage. Egg dislodgement rates (EDR) increased with increasing time exposure to rain, wind, and rain plus wind, and increased for rain and rain plus wind as rain intensity increased. Rain dislodged eggs at the tops of plants and on leaf tops at higher frequencies than eggs lower on plants and on other plant structures. Wind dislodged more eggs towards bottoms of plants and on bolls. EDR after 60 min. exposure was 24 to 30% for rain (0.64 to 5.08 cm/h), 6 to 18% for wind (8.1 to 24.1 kph), and 34 to 48% for rain plus wind. Eggs placed on plants using moistened brushes had higher EDR than plants with moth-laid eggs. Dislodgement results were used to develop a model for H. zea egg mortality due to rain and wind. The model was used to estimate egg dislodgement by rain during field predation tests and can be used in making pest management decisions. Low recovery rates of radioactive Solenopsis invicta following placement of ³²P labelled H. zea eggs on field cotton were investigated using laboratory colonies. Foragers that removed eggs from plants picked up more ³²P than did workers sampled from colonies 12 to 72 h after egg introduction. Problems in finding labelled ants may be associated with low ³²P levels per ant, together with difficulties locating and isolating labelled ants from the population.