The Effectiveness of Coccinellids as Natural Enemies of Aphids in Maize, Beans and Cowpeas Intercrop

A field study was conducted in Busia district of Kenya to elucidate the dynamics of ladybirds in mixed stands of maize, beans and cowpeas to determine their efficacy as sole control measures for Aphids. Maize, beans and cowpeas were intercropped using conventional husbandry practices and the general Coccinellid quantified as follows： Colonies of four Coccinellids, starved for 12 hours to enhance feeding on Aphids were assessed. The effects of weather on the abundance of Coccinellids were also investigated and involved collection of meteorological data from the Busia District Agricultural Office （BDAO） and from Busia Farmers Training Centre （BFTC） and relating them to the abundance and predation values. The predator population was most abundant in the mixed stands of maize and beans （2.33 predators/30 Aphids） as compared to their occurrence in pure stands of cowpeas （0.85 predators/30 Aphids）. The genus Cheilomenes spp. was the most ubiquitous predator with a mean of 4.00 individuals/30 Aphids while Hippodamia variegata was the least abundant predator species with a mean of 0.92 individuals/30 Aphids in all the agro-ecosystems. The larvae of Hippodamia variegata were the most bio-efficient, consuming 32.44 Aphids while their adults were the least bio-efficient, consuming 4.22 individuals for a period of 12 hours. The Coccinellids consumed more Aphids at higher aphid densities （24.05 Aphids） than at lower aphid densities （9.44 Aphids） over the same period of time. Rainfall and relative humidity had significant （F = 3.675; P 〈 0.05） effects on the abundance of Coccinellids. Temperature had significant （F = 3.58; P 〈 0.05） effect on the abundance of Coccinellids though at a lower level. Rainfall （r = -0.162） and relative humidity （r = - 0.084） were both inversely correlated with the abundance of Coccinellids. On the other hand, temperature was positively correlated （r = 0.159） with the prevalence of Coccinellids indicating that warmer and drier conditions favoured their multiplication.

Studies on the Biology and Predatory Potential of <i>Harmonia dimidiata</i>, a Major Predator of <i>Aphis pomi</i>De Geer on Apple Host in India

Observations were made on young nursery plants and apple orchards to record the coccinellid predators of Aphis pomi De Geer on apple plants in Himachal Pradesh which is main apple growing state of India. Nine species of lady bird beetles were observed feeding on green apple aphid, Aphis pomi De Geer on the apple nursery plants of Mashobra locality of Shimla district and Ner Chowk locality of Mandi district of Himachal Pradesh, India. On the basis of general observations, it was found that the larvae of beetle Harmonia dimidiata (F.), are very active to feed on the nymphs of green apple aphid. Therefore, it was considered worthwhile to investigate the biology and feeding potential of this beetle on green apple aphid from biological control point of view.

Botanicals, selective insecticides, and predators to control Diaphorina citri （Hemiptera： Liviidae） in citrus orchards

The Asian citrus psyllid （ACP） Diaphorina citri Kuwayama vectors pathogens that cause huanglongbing （HLB） or citrus greening devastating and economically im- portant disease present in most citrus growing regions. Young citrus shoots are required for psyllid reproduction and development. During winter citrus trees produce little or no new growth. Overwintering adults reproduce in spring on newly emerging shoots also attractive to other pests and beneficial insects. Botanicals and relatively selective insecti- cides could help to conserve beneficial insects and reduce pest resistance to insecticides. Sprays of Azadirachtin （Neem）, Tropane （Datura）, Spirotetramat, Spinetoram, and broad- spectrum Imidacloprid were evaluated to control ACP in spring and summer on 10-year-old ＂Kinow＂ Citrus reticulata Blanco trees producing new growth. Psyllid populations were high averaging 5-9 nymphs or adults per sample before treatment application. Nymphs or adults were significantly reduced to 0.5-1.5 per sample in all treatments for 3 weeks, aver- age 61%-83% reduction. No significant reduction in ladybeetles Adalia bipunctata, Ane- glei scardoni, Cheilomenes sexmaculata, and Coccinella septempunctata was observed. Syrphids, spiders and green lacewings were reduced in treated trees except with Tropane. Studies are warranted to assess impact of these predators on ACP and interaction with insecticides. Observed reduction in ACP populations may not be enough considering its reproductive potential and role in the spread of HLB. Follow-up sprays may be required to achieve additional suppression using rotations of different insecticides.

Functional response of the ladybird, Cydonia vicina nilotica to cowpea aphid, Aphis craccivora in the laboratory

The functional response of Cydonia vicina nilotica Muls. （Coleoptera： Coccinellidae） to six densities of Aphis craccivora Koch （Homoptera： Aphididae） nymphs on broad bean （Viciafaba Linn.） was investigated in the laboratory. A linear relationship between the rate of consumption and prey density was observed with r^2 values between 0.58 and 0.97. Plotting prey density against prey killed by four larval instars, and adult males and females of C. vicina nilotica fit well with the type Ⅱ model of Holling＇ s disc equation. Adult females consumed the highest number of prey, followed by fourth instars and adult males. Based on the functional response data, the model predicts a maximum of 144.9, 116.3, 86.2, 80.0, 72.5 and 20.0 nymphs to be consumed per day by an individual adult female, fourth instar, adult male, third, second and first instars, respectively. The differences in the responses of the predator to aphid densities are discussed.

Use of ryegrass strips to enhance biological control of aphids by ladybirds in wheat fields

Non-crop habitats may play a vital role in conservation biological control. This study tested the effect of ryegrass （Lolium multiflorum L.） strips on aphid and la- dybird populations in adjacent winter wheat fields. The field experiment was conducted in three ryegrass-margin wheat plots and three control plots in 2010 in North China. In spring, the same aphid species, Sitobion miscanthi （Takahashi）, was found in both the ryegrass strips and wheat plots. The population density of ladybirds in the ryegrass strips （3.5 4- 0.9/m2） was significantly higher than in the wheat plots （1.5 4- 0.5/m2）. We cut the ryegrass, forcing the ladybirds to migrate to the wheat fields. Three and eight days after cutting the ryegrass, the aphid numbers in the ryegrass-margin wheat plots decreased significantly： they were 19.9% and 53.6%, respectively, lower than in control plots. In the early period of ladybird population development, the percentage of larvae was greater in the ryegrass-margin wheat plots than in controls, and the peak number of pupae in the ryegrass-margin wheat plots occurred 5 days earlier than in the control plots. The results suggest that ryegrass strips may promote the development of ladybird populations. Cutting ryegrass can manipulate ladybirds to enhance biological aphid control in wheat fields. The efficiency of this management approach is discussed.

Life history and life table analysis of the whitefly predator Delphastus catalinae （Coleoptera： Coccinellidae） on collards

The ladybeetle, Delphastus catalinae (Horn), is one of the most commonly usedpredacious natural enemies being commercially reared for controlling whiteflies, including Bemisiatabaci (Gennadius) biotype B (= B. argentifolii Bellows and Perring), on various ornamental andvegetable crops under greenhouse conditions. The development, survivorship, and fecundity of D.catalinae feeding on B. tabaci biotype B on collard plants were determined in the laboratory, andthe age-specific life table parameters were analyzed based on the life history data. Developmentaltime was 4.0,1.9,1.1,1.4,5.2, and 5.3 days for eggs, first, second, third, fourth instars, andpupae, respectively, with an average of 18.9 days from oviposition to adult emergence for bothsexes, 19.0 days for females, and 18.8 days for males. Adult longevities averaged 146.6 days forboth sexes, 122.6 days for females, and 170.5 days for males. After an average 4.9 dayspreoviposition period, females laid a mean of 5.6 eggs per day over a 97.0-day period. Netreproductive rate (R_0) and gross reproductive rate (Σm_x) were estimated by life table analysis at276.8 and 325.1, respectively. Generation time (T) and doubling time (DT) were 35.6 and 4.8 daysrespectively, and the intrinsic rate of natural population increase (r_m) was estimated at 0.158, orl= 1.171 for the finite rate of increase. The r_m value of D. catalinae is similar to or higherthan those of the whitefly feeding on most vegetable and ornamental crops, indicating that theladybeetle is capable of regulating populations of B. tabaci biotype B and other whiteflies undergreenhouse conditions.

FUNCTIONAL RESPONSE AND PLANT PREFERENCE OF NEPHASPIS OCULATUS (COLEOPTERA: COCCINELLIDAE), PREYING ON BEMISIA ARGENTIFOLII (HOMOPTERA: ALEYRODIDAE) IN THE LABORATORY

The predatory behavior and functional response of all larval stages and adults of Nephaspis oculatus (Blatchley), a predacious coccinellid, on various egg densities of Bemisia argentifolii Bellows & Perring, and prey preference of adult N. oculatus, were studied in the laboratory. Daily consumption of eggs of B. argentifolii by N. oculatus was evaluated at six different densities to obtain functional response curves for all active stages of the coccinellid. Bemisia argentifolii eggs were offered to N. oculatus on collard leaf disks in Petri dish arenas over a 24\|h period at 26 7 2℃ and a photoperiod of 14∶10 (L∶D) h. Linear relationships were observed between percentage prey consumed and prey density, with r 2 values between 0 82-0 99 for all stages except for the fourth instar that had a smaller r 2 value (0 64). Functional response curves of prey consumption by N. oculatus against density of B. argentifolii eggs fitted the type II model of Holling's disc equation for all larval stages and both the male and female adults. Adult females consumed more prey than adult males. The maximum theoretical number of prey consumed per day increased with larval development. The fourth instar was the most effective larval predator, followed by the third instar, the second instar, and finally, the first instar. Based on the functional response parameters, a maximum of 321, 312, 237, 229, 73, and 34 B. argentifolii eggs could be attacked by an adult female, a fourth instar, an adult male, a third instar, a second instar, and a first instar of N. oculatus, respectively. Nephaspis oculatus adults strongly preferred collard to tomato, soybean, eggplant or sweetpotato for oviposition and foraging. Nephaspis oculatus did not deposit any eggs on soybean and tomato.